Limited Vaccine Supply Research Articles

A Scoping Review of Factors Affecting COVID-19 Vaccination Uptake and Deployment in Global Healthcare Systems.

Introduction: COVID-19 vaccines were rapidly developed and deployed on a large scale during a global crisis. A range of deployment strategies were used globally to maximize vaccine uptake. In this scoping review, we identify and analyze the main healthcare system and policy factors that guided and influenced COVID-19 vaccination deployment and uptake globally. Materials and Methods: JBI guidelines, Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR), and the population, concept, and context (PCC) framework were applied. Studies on individual COVID-19 vaccination factors, such as vaccine hesitancy, were excluded. The search was last conducted in May 2024 yielding 26,686 articles from PubMed, Embase, CINAHL, Scopus, and COVID-19 websites. A total of 47 articles and 3 guidance documents were included. The results of the thematic analysis were mapped to the Consolidated Framework for Implementation Research (CFIR). Results: The results found the following healthcare system and policy factors as integral to COVID-19 vaccination: types of vaccine products, healthcare workforce capacity, procurement strategies, distribution and cold-chain capacity, partnership, coordination, and leadership, information, communication, and registration strategies, delivery models, organizations, the existing health systems and policies on prioritization of at-risk groups and deployment plans. Discussion: Globally, COVID-19 vaccination programs responded to the pandemic by leveraging and reforming the existing healthcare systems, relying on strong leadership and global cooperation (such as the COVID-19 Vaccines Global Access Initiative). Deployment was enabled by effective communication and adoption of innovative technologies using data-driven policies to create high vaccine demand while overcoming limited vaccine supply and rapidly adapting to uncertainties.

Fuzzy logic for the management of vaccination during pandemics: A spread-rate-based approach

<p>Pandemics, such as coronavirus disease COVID-19 are known to cause massive damage to the world's economic growth and their impacts are serious and influence across every aspect of social structure. The most inevitable factor in responding to the disaster of pandemics is the right management in terms of allocating a limited vaccine supply. The focus of this research work is to utilize a fuzzy logic inference system in the allocation of vaccine doses to the regional authorities by a central authority. The objective is obtained by designing a system based on fuzzy logic that considers the spread rate as the input to infer the vaccination rate of the local population. This system makes it possible for sufficient doses of vaccines to be allotted to the prioritized regions where the severity of the spread rate is a concern and vaccines are not held up in regions where the severity of the spread rate is lesser. The designed system is verified using MATLAB software, which shows that this method can ensure an effective and efficient allocation of vaccination in the local regions and aid the fight against the disastrous spread of the disease.</p>

Evaluation of Rhode Island's Early Geographic COVID-19 Vaccine Prioritization Policy.

Objectives. To determine whether geographic prioritization of limited COVID-19 vaccine supply was effective for reducing geographic disparities in case rates. Methods. Rhode Island allocated a portion of the initial COVID-19 vaccine supply to residents of Central Falls, a community already affected by structural policies and inadequate systems that perpetuate health inequities and experiencing disproportionately high COVID-19 morbidity and mortality. The policy was implemented with a culturally and linguistically appropriate community engagement plan and was intended to reduce observed disparities. Using a Bayesian causal analysis with population surveillance data, we evaluated the impact of this prioritization policy on recorded cases over the subsequent 16 weeks. Results. Early geographic prioritization of Central Falls accelerated vaccine uptake, averting an estimated 520 cases (95% confidence interval = 22, 1418) over 16 weeks and reducing cases by approximately 34% during this period (520 averted vs 1519 expected without early prioritization). Conclusions. Early geographic prioritization increased vaccine uptake and reduced cases in Central Falls, thereby reducing geographic disparities. Public Health Implications. Public health institutions should consider geographic prioritization of limited vaccine supply to reduce geographic disparities in case rates. (Am J Public Health. 2024;114(S7):S580-S589. https://doi.org/10.2105/AJPH.2024.307741).

Vaccine inequalities, hesitancy, and media-focused public health interventions in English-speaking West-African Countries

Background: Vaccine hesitancy poses a significant challenge to public health efforts in English-speaking West-African countries amidst the COVID-19 pandemic. This study aims to examine the multifaceted factors contributing to vaccine hesitancy in the region, including issues of trust, misinformation, cultural beliefs, and access barriers. Methods: This study reviewed data from three African countries, Nigeria, Ghana, and the Gambia, to analyze attitudes towards vaccination. It also assessed variations in attitudes across these countries and compared them with attitudes in the western world. Qualitative and quantitative methods were employed to gather and analyze data on vaccine hesitancy and related factors. Results: The study found substantial variation in attitudes towards vaccination across the surveyed countries and compared to the western world. Factors contributing to vaccine hesitancy included historical injustices, misinformation, cultural beliefs, and access barriers such as limited healthcare infrastructure and vaccine supply constraints. Media-focused public health interventions were identified as crucial in addressing vaccine inequalities and enhancing vaccine acceptance. Conclusion: Overcoming vaccine hesitancy in West Africa requires tailored approaches that acknowledge and address historical injustices and inequities, emphasize culturally appropriate messaging, and utilize existing community infrastructure to deliver accurate information. Targeted communication strategies are essential to combat misinformation and enhance vaccine acceptance. By analyzing the intersection of vaccine hesitancy, media interventions, and public health challenges, this study underscores the need for comprehensive and community-engaged campaigns to promote vaccination and combat the spread of COVID-19 in West Africa.

Impact of the first year of COVID-19 vaccination strategy in Brazil: an ecological study

ObjectivesNo consensus exists about the best COVID-19 vaccination strategy to be adopted by low-income and middle-income countries. Brazil adopted an age-based calendar strategy to reduce mortality and the burden on...

Assessing New York City's COVID-19 Vaccine Rollout Strategy: A Case for Risk-Informed Distribution.

This study reviews the impact of eligibility policies in the early rollout of the COVID-19 vaccine on coverage and probable outcomes, with a focus on New York City. We conducted a retrospective ecological study assessing age 65+, area-level income, vaccination coverage, and COVID-19 mortality rates, using linked Census Bureau data and New York City Health administrative data aggregated at the level of modified zip code tabulation areas (MODZCTA). The population for this study was all individuals in 177 MODZCTA in New York City. Population data were obtained from Census Bureau and New York City Health administrative data. The total mortality rate was examined through an ordinary least squares (OLS) regression model, using area-level wealth, the proportion of the population aged 65 and above, and the vaccination rate among this age group as predictors.Low-income areas with high proportions of older people demonstrated lower coverage rates (mean vaccination rate 52.8%; maximum coverage 67.9%) than wealthier areas (mean vaccination rate 74.6%; maximum coverage 99% in the wealthiest quintile) in the first 3months of vaccine rollout and higher mortality over the year. Despite vaccine shortages, many younger people accessed vaccines ahead of schedule, particularly in high-income areas (mean coverage rate 60% among those 45-64years in the wealthiest quintile). A vaccine program that prioritized those at greatest risk of COVID-19-associated morbidity and mortality would have prevented more deaths than the strategy that was implemented. When rolling out a new vaccine, policymakers must account for local contexts and conditions of high-risk population groups. If New York had focused limited vaccine supply on low-income areas with high proportions of residents 65 or older, overall mortality might have been lower.

Vaccination Strategies based on a Mathematical Model of Epidemics Considering the Age Structure of the Population

During the COVID-19 pandemic, it is important to promote the skills needed for analyzing the disease course, including determining the relevance of vaccinations, especially among people who are unfamiliar with computer programming. This paper describes the basic epidemiological model (SIR), its extensions that allow vaccinations, and the emergence of renewed waves of disease growth. It also discusses a literature model, extended SEIRD, which includes a more detailed division of the population into susceptible, latent, symptomatic, and asymptomatic infected, recovered, and dead in eight age groups. Modifying the SEIRD model as shown on the basic SIR model, we analyzed five vaccination strategies, considering the limited vaccine supply, the number of vaccinations performed per day, and their effectiveness. The analysis was performed for a group of one million people, using the parameters of the model characteristic of the COVID-19 pandemic and Sweden's generational structure. We analyzed in terms of reducing both the number of deaths and the incidence of symptomatic infections, which represent the main burden of healthcare.

"It's not that I don't trust vaccines, I just don't think I need them": Perspectives on COVID-19 vaccination.

In Quebec (Canada), the roll-out of the vaccination started slowly in December 2020 due to limited vaccine supply. While the first and second doses were well-accepted among adults and vaccine uptake was above 90%, in late 2021 and 2022, vaccine acceptance decreased for children vaccination and receipt of a 3rd or a 4th dose. In the autumn of 2022, four focus groups were conducted with vaccine-hesitant parents of children aged 0-4 and adults who expressed little intention to receive a booster dose. The objective of this study was to gather participants' perspectives on vaccination in general, on the COVID-19 vaccination campaign and the information available, and to gain insights into the underlying reasons for their low intention of either having their child(ren) vaccinated, or receiving an additional dose of vaccine. A total of 35 participants took part in the focus groups. While participants expressed a certain level of trust and confidence in public health and government authorities regarding pandemic management and the vaccination campaign, they were also concerned that transparent information was lacking to support an informed decision on booster doses and children's vaccination. Many participants felt adequately protected against the infection during the focus groups, citing a lack of perceived benefits as the primary reason for refusing a booster dose. Parents who refused to administer the COVID-19 vaccine to their young children felt that the vaccine was not useful for children and were concerned about potential side effects. The majority reported that their opinions regarding other recommended vaccines had not changed since the beginning of the pandemic. While these results are reassuring, our findings highlight the importance of transparency in public health communications about vaccines to increase confidence and to develop strategies to address vaccine fatigue and complacency toward COVID-19 vaccines.

The Sooner, the Better? Optimal Vaccination Policy with Limited Vaccine Supply

The Sooner, the Better? Optimal Vaccination Policy with Limited Vaccine Supply

Optimal vaccination ages for emerging infectious diseases under limited vaccine supply.

Rational allocation of limited vaccine resources is one of the key issues in the prevention and control of emerging infectious diseases. An age-structured infectious disease model with limited vaccine resources is proposed to explore the optimal vaccination ages. The effective reproduction number [Formula: see text] of the epidemic disease is computed. It is shown that the reproduction number is the threshold value for eradicating disease in the sense that the disease-free steady state is globally stable if [Formula: see text] and there exists a unique endemic equilibrium if [Formula: see text]. The effective reproduction number is used as an objective to minimize the disease spread risk. Using the epidemic data from the early spread of Wuhan, China and demographic data of Wuhan, we figure out the strategies to distribute the vaccine to the age groups to achieve the optimal vaccination effects. These analyses are helpful to the design of vaccination schedules for emerging infectious diseases.

Pandemic disruptions in vaccine uptake in a low-income setting: a qualitative inquiry

BackgroundWhile the COVID-19 pandemic has exposed the vulnerabilities of immunization delivery systems globally, the devastating impact of the pandemic on immunization delivery is most pronounced in low and middle-income countries like Pakistan. We conducted a qualitative study to capture the views and experiences of parents and healthcare workers (HWs) and assess the impact of the COVID-19 pandemic on childhood routine immunization (CRI) and COVID-19 vaccination in Pakistan.MethodsWe used a qualitative research design with a purposive sampling approach. Semi-structured interviews (via telephone) and focus group discussions (via Zoom) were conducted with parents/child caregivers and HWs, respectively. All qualitative interviews were conducted between February and July 2021 from three sites (two urban and one rural) in Sindh, Pakistan. Interviews were audio-recorded, transcribed, and coded for a team-based thematic analysis.ResultsOverall, most parents and HWs indicated a strong trust in the benefits of CRI; nonetheless, a substantial disruption in the delivery and uptake of these services was also reported. The barriers towards CRI included closed vaccination centers, drastic reduction in outreach programs, lack of information for parents/child caregivers on vaccine availability, fear in the community regarding vaccine safety, limited vaccine supply, and a lack of healthcare staff. For COVID-19 vaccines, challenges cited included skepticism about the reality of the pandemic and confusion over COVID-19 vaccines due to conflicting (or mis-or-dis) information. Both participant groups showed a willingness to integrate COVID-19 vaccination into Pakistan’s Expanded Program for Immunization if required in the future.ConclusionDuring the COVID-19 pandemic, disruptions of regular immunization delivery in Pakistan were not due to parental unwillingness to vaccinate, but rather to social and logistical challenges caused by a rapidly changing context and difficulties in providing vaccination services safely. Barriers to vaccine access and concerns about COVID-19 exposure during clinic visits also contributed to uncertainty regarding immunization services early in the pandemic. For catchup campaigns and future pandemics, more than focusing interventions on persuading people, strategic approaches to building resilience through system-based interventions, such as investing in surge capacity in the immunization workforce to bounce back quickly after the first shock are required.

Challenges of COVID‐19 vaccination program in rural areas of Eastern Indonesia: A qualitative study from a multistakeholder perspective

AbstractThis research aimed to explore the challenges of the COVID‐19 vaccination program from the perspective of multiple stakeholders in rural areas of eastern Indonesia. This qualitative participatory action research involved 115 participants selected from various groups in 20 subdistricts across five provinces, including Health Service workers, police staff monitoring the vaccination program, religious figures, and adult and youth community leaders. Furthermore, focus group discussion was conducted using semi‐structured interview guidelines based on the WHO Strategic Advisory Group of Experts (SAGE) for vaccine and immunization model. The manifest content approach was employed to analyze the visible contents within the text. Implementation of the vaccination program was complicated by contextual, individual, and group factors, as well as vaccine and vaccination‐specific factors. The contextual factors were socioeconomic, religious, and cultural conditions, changes in government policies, and geographical and climatic obstacles. Meanwhile, examples of group and individual factors were people's beliefs of COVID‐19 being harmless and their invulnerability to the disease, along with misinformation and disinformation about vaccination, and fatalistic attitudes. Factors related to the vaccine and vaccination process include limited vaccine supplies, inadequate supporting facilities, and insufficient administration of vaccines. Multiple and complex challenges of COVID‐19 vaccination in the rural areas of eastern Indonesia need attention from the local and national government, as well as other parties including the private sector, socio‐religious figures and organizations, and the media.

A Multi-Objective Simulated Annealing Local Search Algorithm in Memetic CENSGA: Application to Vaccination Allocation for Influenza

Flu vaccine allocation is of great importance for safeguarding public health and mitigating the impact of influenza outbreaks. In this regard, decision-makers face multifaceted challenges, including limited vaccine supply, targeting vulnerable people, adapting to regional variations, ensuring fairness in distribution, and promoting public trust. The objective of this work is to address the vaccination allocation problem by introducing a novel optimization scheme with the simulated annealing (SA) algorithm. A dual-objective model is developed to both manage infection rates and minimize the unit cost of the vaccination campaign. The proposed approach is designed to promote convergence toward the best Pareto front in multi-objective optimization, wherein SA attempts to embed diversity and uniformity within a memetic version of the controlled elitism nondominated sorting genetic algorithm (CENSGA). To model the underlying vaccination allocation problem, the dynamics of the disease are described using the susceptible–exposed–infectious–recovered (SEIR) epidemiological model to better express hidden flu characteristics. This model specifically analyzes the effects of pulsive vaccination allocation in two phases aiming to minimize the number of infected individuals to an acceptable level in a finite amount of time, which can help in stabilizing the model against sudden flu endemics over the long run. The computational experiments show that the proposed algorithm effectively explores the extensive search space of the vaccination allocation problem. The results of the suggested framework indicate that the obtained Pareto front best represents complete vaccination campaigns. The findings of this research can help in evidence-based decision making that can optimize flu vaccine distribution, contribute to the prevention of illness and reduction in hospitalizations, and potentially save countless lives.

Optimal vaccination strategies for COVID-19 in population migration between two regions scenario

ABSTRACT Population movements had a significant impact on the spread of COVID-19, and vaccination is considered the most effective means for humans to face viral infections. This study identifies the optimal control strategy for COVID-19 prevention and control, and explores the impact of short-term and long-term migration on the optimal proportion of vaccine allocation between two regions. We proposed to establish the SIR (Susceptible-Infectious-Recovered) model and determine the stability by calculating the disease free equilibrium and Jacobi matrix of the model. We then established the vaccine optimization model, solved the optimal vaccine distribution strategy by gradient descent method and explored the impact of short-term and long-term migration on the optimal vaccine allocation ratio. The stability analysis revealed that the virus could not be eliminated only by reducing the migration rates and infection rates. we introduced the vaccine methods and obtained the optimal vaccine allocation ratio in Shenzhen and Hong Kong as p 1 : p 2 = 0.000341 : 0.001739 , and the daily vaccination rate we need to impose in each region as p 1 : p 2 = 0.00068 : 0.001901 . The presence or absence of short-term migration had no greater impact on the distribution of the vaccine, whereas R v with long-term migration had a greater effect than no migration. We found that migration rates could not eliminate the outbreak in both regions and that adopting an effective vaccine distribution strategy could be more effective in eliminating the outbreak. And for different allocation scenarios with limited vaccine supply, we obtained the optimal allocation most favorable to control the epidemic.

Optimal vaccine allocation for the control of sexually transmitted infections.

The burden of sexually transmitted infections (STIs) poses a challenge due to its large negative impact on sexual and reproductive health worldwide. Besides simple prevention measures and available treatment efforts, prophylactic vaccination is a powerful tool for controlling some viral STIs and their associated diseases. Here, we investigate how prophylactic vaccines are best distributed to prevent and control STIs. We consider sex-specific differences in susceptibility to infection, as well as disease severity outcomes. Different vaccination strategies are compared assuming distinct budget constraints that mimic a scarce vaccine stockpile. Vaccination strategies are obtained as solutions to an optimal control problem subject to a two-sex Kermack-McKendrick-type model, where the control variables are the daily vaccination rates for females and males. One important aspect of our approach relies on conceptualizing a limited but specific vaccine stockpile via an isoperimetric constraint. We solve the optimal control problem via Pontryagin's Maximum Principle and obtain a numerical approximation for the solution using a modified version of the forward-backward sweep method that handles the isoperimetric budget constraint in our formulation. The results suggest that for a limited vaccine supply ([Formula: see text]-[Formula: see text] vaccination coverage), one-sex vaccination, prioritizing females, appears to be more beneficial than the inclusion of both sexes into the vaccination program. Whereas, if the vaccine supply is relatively large (enough to reach at least [Formula: see text] coverage), vaccinating both sexes, with a slightly higher rate for females, is optimal and provides an effective and faster approach to reducing the prevalence of the infection.

Covid-19 Vaccine Acceptance and Uptake in Bangkok, Thailand: Cross-Sectional Survey via Social Media.

The third, most severe COVID-19 wave in mid-2021 coincided with dual challenges of limited vaccine supply and lagging acceptance in Bangkok, Thailand. Understanding of persistent vaccine hesitancy during the "608" campaign to vaccinate the over 60 years and eight medical risk groups was needed. On-the ground surveys place further demands on resources and are scale-limited. We leveraged the University of Maryland COVID-19 Trends and Impact Survey (UMD-CTIS) - a digital health survey conducted among daily Facebook user samples - in this this densely populated, high-transmission region with high Facebook social media use to fill this need and inform regional vaccine roll-out policy. The aims of this study were to characterize COVID-19 vaccine hesitancy, frequent reasons for hesitancy, mitigating risk behaviors, and most trusted sources of COVID-19 information through which to combat vaccine hesitancy in Bangkok, Thailand during the "608" vaccine campaign. UMD-CTIS is an online, cross-sectional survey conducted among daily, statistical samples of the Facebook active user base. We analyzed 34,423 Bangkok UMD-CTIS surveys conducted June-October 2021 coinciding with the third COVID-19 wave. Sampling consistency and representativeness of the UMD-CTIS respondents were evaluated by comparing distributions of demographics, 608 priority groups, and vaccine uptake over time with source population benchmark data. Estimates of vaccine hesitancy in Bangkok and 608 priority groups were tracked over time. Frequently cited hesitancy reasons and trusted information sources were identified by 608 group and degree of hesitancy. Kendall's Tau was used to test statistical associations between vaccine acceptance and vaccine hesitancy. UMD-CTIS Bangkok respondents had similar demographics over weekly samples and compared to the Bangkok source population. Respondents self-reported fewer pre-existing health conditions such as chronic kidney disease and cardiovascular disease compared to census but had similar prevalence of the important COVID-19 risk factor diabetes. UMD-CTIS vaccine uptake rose in parallel with national vaccination statistics, while vaccine hesitancy and degree of hesitancy declined [-7% hesitant per week]. Concerns about vaccination side effects (63%) and wanting to wait and see (62%) were selected most frequently, while "not liking vaccines" (7%) and "religious objections'' (1%" least so, regardless of risk group, time period, or level of vaccine acceptance. Greater vaccine acceptance was associated positively with wanting to "Wait and See'' and negatively with "Don't Believe I Need [the vaccine]" (Kendall's Tau 0.21 and -0.22, respectively, adjusted P values <0.001). Scientists and health experts were most frequently cited as trusted COVID-19 information sources (97%), even within the "Probably Not" and "Definitely Not" groups. These findings provide policy and health experts with evidence that vaccine hesitancy was declining, albeit slowly, over the study timeframe. Hesitancy and trust analyses among the unvaccinated support Bangkok policy measures to address vaccine safety and efficacy concerns through health experts, rather than government or religious officials. Large-scale surveys enabled by existing, widespread digital networks, offer an insightful, minimal-infrastructure resource for informing region-specific health policy needs.

Priority age targets for COVID-19 vaccination in Ethiopia under limited vaccine supply

The worldwide inequitable access to vaccination claims for a re-assessment of policies that could minimize the COVID-19 burden in low-income countries. Nine months after the launch of the national vaccination program in March 2021, only 3.4% of the Ethiopian population received two doses of COVID-19 vaccine. We used a SARS-CoV-2 transmission model to estimate the level of immunity accrued before the launch of vaccination in the Southwest Shewa Zone (SWSZ) and to evaluate the impact of alternative age priority vaccination targets in a context of limited vaccine supply. The model was informed with available epidemiological evidence and detailed contact data collected across different geographical settings (urban, rural, or remote). We found that, during the first year of the pandemic, the mean proportion of critical cases occurred in SWSZ attributable to infectors under 30 years of age would range between 24.9 and 48.0%, depending on the geographical setting. During the Delta wave, the contribution of this age group in causing critical cases was estimated to increase on average to 66.7–70.6%. Our findings suggest that, when considering the vaccine product available at the time (ChAdOx1 nCoV-19; 65% efficacy against infection after 2 doses), prioritizing the elderly for vaccination remained the best strategy to minimize the disease burden caused by Delta, irrespectively of the number of available doses. Vaccination of all individuals aged ≥ 50 years would have averted 40 (95%PI: 18–60), 90 (95%PI: 61–111), and 62 (95%PI: 21–108) critical cases per 100,000 residents in urban, rural, and remote areas, respectively. Vaccination of all individuals aged ≥ 30 years would have averted an average of 86–152 critical cases per 100,000 individuals, depending on the setting considered. Despite infections among children and young adults likely caused 70% of critical cases during the Delta wave in SWSZ, most vulnerable ages should remain a key priority target for vaccination against COVID-19.

Real-time prediction model of cVDPV2 outbreaks to aid outbreak response vaccination strategies.

Circulating vaccine-derived poliovirus outbreaks are spreading more widely than anticipated, which has generated a crisis for the global polio eradication initiative. Effectively responding with vaccination activities requires a rapid risk assessment. This assessment is made difficult by the low case-to-infection ratio of type 2 poliovirus, variable transmissibility, changing population immunity, surveillance delays, and limited vaccine supply from the global stockpile. The geographical extent of responses have been highly variable between countries. We develop a statistical spatio-temporal model of short-term, district-level poliovirus spread that incorporates known risk factors, including historical wild poliovirus transmission risk, routine immunization coverage, population immunity, and exposure to the outbreak virus. We find that proximity to recent cVDPV2 cases is the strongest risk factor for spread of an outbreak, and find significant associations between population immunity, historical risk, routine immunization, and environmental surveillance (p<0.05). We examine the fit of the model to type 2 vaccine derived poliovirus spread since 2016 and find that our model predicts the location of cVDPV2 cases well (AUC=0.96). We demonstrate use of the model to estimate appropriate scope of outbreak response activities to current outbreaks. As type 2 immunity continues to decline following the cessation of tOPV in 2016, outbreak responses to new cVDPV2 detections will need to be faster and larger in scope. We provide a framework that can be used to support decisions on the appropriate size of a vaccination response when new detections are identified. While the model does not account for all relevant local factors that must be considered in the overall vaccination response, it enables a quantitative basis for outbreak response size.

Comorbidity-stratified estimates of 30-day mortality risk by age for unvaccinated men and women with COVID-19: a population-based cohort study

BackgroundThe mortality risk following COVID-19 diagnosis in men and women with common comorbidities at different ages has been difficult to communicate to the general public. The purpose of this study was to determine the age at which unvaccinated men and women with common comorbidities have a mortality risk which exceeds that of 75- and 65-year-old individuals in the general population (Phases 1b/1c thresholds of the Centre for Disease Control Vaccine Rollout Recommendations) following COVID-19 infection during the first wave.MethodsWe conducted a population-based retrospective cohort study using linked administrative datasets in Ontario, Canada. We identified all community-dwelling adults diagnosed with COVID-19 between January 1 and October 31st, 2020. Exposures of interest were age (modelled using restricted cubic splines) and the following conditions: major cardiovascular disease (recent myocardial infarction or lifetime history of heart failure); 2) diabetes; 3) hypertension; 4) recent cancer; 5) chronic obstructive pulmonary disease; 6) Stages 4/5 chronic kidney disease (CKD); 7) frailty. Logistic regression in the full cohort was used to estimate the risk of 30-day mortality for 75- and 65-year-old individuals. Analyses were repeated after stratifying by sex and medical condition to determine the age at which 30-day morality risk in strata exceed that of the general population at ages 65 and 75 years.ResultsWe studied 52,429 individuals (median age 42 years; 52.5% women) of whom 417 (0.8%) died within 30 days. The 30-day mortality risk increased with age, male sex, and comorbidities. The 65- and 75-year-old mortality risks in the general population were exceeded at the youngest age by people with CKD, cancer, and frailty. Conversely, women aged < 65 years who had diabetes or hypertension did not have higher mortality than 65-year-olds in the general population. Most people with medical conditions (except for Stage 4–5 CKD) aged < 45 years had lower predicted mortality than the general population at age 65 years.ConclusionThe mortality risk in COVID-19 increases with age and comorbidity but the prognostic implications varied by sex and condition. These observations can support communication efforts and inform vaccine rollout in jurisdictions with limited vaccine supplies.

Quantifying the effect of delaying the second COVID-19 vaccine dose in England: a mathematical modelling study

The UK was the first country to start national COVID-19 vaccination programmes, initially administering doses 3 weeks apart. However, early evidence of high vaccine effectiveness after the first dose and the emergence of the SARS-CoV-2 alpha variant prompted the UK to extend the interval between doses to 12 weeks. In this study, we aimed to quantify the effect of delaying the second vaccine dose in England. We used a previously described model of SARS-CoV-2 transmission, calibrated to COVID-19 surveillance data from England, including hospital admissions, hospital occupancy, seroprevalence data, and population-level PCR testing data, using a Bayesian evidence-synthesis framework. We modelled and compared the epidemic trajectory in the counterfactual scenario in which vaccine doses were administered 3 weeks apart against the real reported vaccine roll-out schedule of 12 weeks. We estimated and compared the resulting numbers of daily infections, hospital admissions, and deaths. In sensitivity analyses, we investigated scenarios spanning a range of vaccine effectiveness and waning assumptions. In the period from Dec 8, 2020, to Sept 13, 2021, the number of individuals who received a first vaccine dose was higher under the 12-week strategy than the 3-week strategy. For this period, we estimated that delaying the interval between the first and second COVID-19 vaccine doses from 3 to 12 weeks averted a median (calculated as the median of the posterior sample) of 58 000 COVID-19 hospital admissions (291 000 cumulative hospitalisations [95% credible interval 275 000-319 000] under the 3-week strategy vs 233 000 [229 000-238 000] under the 12-week strategy) and 10 100 deaths (64 800 deaths [60 200-68 900] vs 54 700 [52 800-55 600]). Similarly, we estimated that the 3-week strategy would have resulted in more infections compared with the 12-week strategy. Across all sensitivity analyses the 3-week strategy resulted in a greater number of hospital admissions. In results by age group, the 12-week strategy led to more hospitalisations and deaths in older people in spring 2021, but fewer following the emergence of the delta variant during summer 2021. England's delayed-second-dose vaccination strategy was informed by early real-world data on vaccine effectiveness in the context of limited vaccine supplies in a growing epidemic. Our study shows that rapidly providing partial (single-dose) vaccine-induced protection to a larger proportion of the population was successful in reducing the burden of COVID-19 hospitalisations and deaths overall. UK National Institute for Health Research; UK Medical Research Council; Community Jameel; Wellcome Trust; UK Foreign, Commonwealth and Development Office; Australian National Health and Medical Research Council; and EU.