Waning Of Vaccine-induced Immunity Research Articles

Effects of vaccination on the two-strain transmission dynamics of COVID-19: Dougherty County, Georgia, USA, as a case study.

The emergence of multiple strains of SARS-COV-2 has made it complicated to predict and control the COVID-19 pandemic. Although some vaccines have been effective in reducing the severity of the disease, these vaccines are designed for a specific strain of the virus and are usually less effective for other strains. In addition, the waning of vaccine-induced immunity, reinfection of recovered people, and incomplete vaccination are challenging to the vaccination program. In this study, we developed a detailed model to describe the multi-strain transmission dynamics of COVID-19 under vaccination. We implemented our model to examine the impact of inter-strain transmission competition under vaccination on the critical outbreak indicators: hospitalized cases, undiagnosed cases, basic reproduction numbers, and the overtake-time by a new strain to the existing strain. In particular, our results on the dependence of the overtake-time on vaccination rates, progression-to-infectious rate, and relative transmission rates provide helpful information for managing a pandemic with circulating two strains. Furthermore, our results suggest that a reduction in the relative transmission rates and a decrease in vaccination dropout rates or an increase in vaccination rates help keep the reproduction number of both strains below unity and keep the number of hospitalized cases and undiagnosed cases at their lowest levels. Moreover, our analysis shows that the second and booster-dose vaccinations are useful for further reducing the reproduction number.

Genomic surveillance of SARS-CoV-2 in COVID-19 vaccinated healthcare workers in Lebanon

BackgroundThe emergence of SARS-CoV-2 variants including the Delta and Omicron along with waning of vaccine-induced immunity over time contributed to increased rates of breakthrough infection specifically among healthcare workers (HCWs). SARS-CoV-2 genomic surveillance is an important tool for timely detection and characterization of circulating variants as well as monitoring the emergence of new strains. Our study is the first national SARS-CoV-2 genomic surveillance among HCWs in Lebanon.MethodsWe collected 250 nasopharyngeal swabs from HCWs across Lebanon between December 2021 and January 2022. Data on the date of positive PCR, vaccination status, specific occupation, and hospitalization status of participants were collected. Extracted viral RNA from nasopharyngeal swabs was converted to cDNA, library prepped using the coronaHIT method, followed by whole genome sequencing on the Illumina NextSeq 500 platform.ResultsA total of 133 (57.1%) samples belonging to the Omicron (BA.1.1) sub-lineage were identified, as well as 44 (18.9%) samples belonging to the BA.1 sub-lineage, 28 (12%) belonging to the BA.2 sub-lineage, and only 15 (6.6%) samples belonging to the Delta variant sub-lineage B.1.617.2. These results show that Lebanon followed the global trend in terms of circulating SARS-CoV-2 variants with Delta rapidly replaced by the Omicron variant.ConclusionThis study underscores the importance of continuous genomic surveillance programs in Lebanon for the timely detection and characterization of circulating variants. The latter is critical to guide public health policy making and to timely implement public health interventions.

Waning Effectiveness of the BNT162b2 Vaccine Against Infection in Adolescents in Israel.

The short-term effectiveness of a 2-dose regimen of the BioNTech/Pfizer BNT162b2 vaccine for adolescents has been demonstrated. However, little is known about the long-term effectiveness in this age group. It is known, however, that waning of vaccine-induced immunity against infection in adult populations is evident within a few months. Leveraging the database of Maccabi Healthcare Services (MHS), we conducted a matched case-control design for evaluating the association between time since vaccination and the incidence of infections, where 2 outcomes were evaluated: documented SARS-CoV-2 infection (regardless of symptoms) and symptomatic infection (COVID-19). Cases were defined as individuals aged 12-16 with a positive polymerase chain reaction (PCR) test occurring between 15 June and 8 December 2021, when the Delta variant was dominant in Israel. Controls were adolescents who had not tested positive previously. We estimated a peak vaccine effectiveness between 2 weeks and 3 months following receipt of the second dose, with 85% (95% confidence interval [CI]: 84-86%) and 90% (95% CI: 89-91%) effectiveness against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and coronavirus disease 2019 (COVID-19), respectively. However, in line with findings for adults, waning effectiveness was evident. Long-term protection was reduced to 73% (95% CI: 68-77%) against infection and 79% (95% CI: 73-83%) against COVID-19 3-5 months after the second dose and waned to 53% (95% CI: 46-60%) against infection and 66% (95% CI: 59-72%) against COVID-19 after 5 months. Although vaccine-induced protection against both infection and COVID-19 continues over time in adolescents, the protection wanes with time since vaccination, starting 3 months after inoculation and continuing for more than 5 months.

Enhanced Vaccine Effectiveness during the Delta Phase of the COVID-19 Pandemic in the Medicare Population Supports a Multilayered Prevention Approach.

Throughout the pandemic, individuals 65 years and older have contributed most COVID-19 related deaths. To best formulate effective vaccination and other prevention policies to protect older adults, large scale observational studies of these higher risk individuals are needed. We conducted a Vaccine Effectiveness (VE) study during the B.1.617.2 Delta variant phase of the pandemic in July and August 2021 in a cohort of 17 million Medicare beneficiaries of which 5.7 million were fully vaccinated. We found that individuals fully vaccinated with the Pfizer-BioNTech BNT162b2 and Moderna mRNA-1273 vaccines in January 2021 had 2.5 times higher breakthrough infections and hospitalizations than those fully vaccinated in March 2021, consistent with waning of vaccine-induced immunity. Measuring VE weekly, we found that VE against hospitalization, and even more so against infection, increased from July 2021 through August 2021, suggesting that in addition to the protective role of vaccination, increased masking or social distancing might have contributed to the unexpected increase in VE. Ongoing monitoring of Medicare beneficiaries should be a priority as new variants continue to emerge, and the VE of the new bivalent vaccines remains to be established. This could be accomplished with a large Medicare claims database and the analytics platform used for this study.

A quick scoping review of the first year of vaccination against the COVID-19 pandemic: Do we need more shots or time?

Background:The emergence of new severe acute respiratory syndrome coronavirus 2 variants, along with the waning of vaccine-induced immunity, has increased breakthrough infections and urged booster jabs and debates. In the short term, the administration of booster doses has been reported to be safe and enhance severe acute respiratory syndrome coronavirus 2–specific neutralizing antibody levels. However, the effects of these doses on the pandemic trajectory and herd immunity are unclear. There is insufficient evidence that a third booster shot of the coronavirus disease 2019 (COVID-19) vaccine maintains longer immunity and covers new viral variants. The lack of sufficient evidence, combined with the fact that millions of people have not yet received 1 or 2 jabs of the COVID-19 vaccine, has raised concerns regarding the call for booster vaccinations.Methods:We conducted a quick scoping review to explore the literature on the need for a booster COVID-19 vaccination from January 1, 2021, to April 30, 2022.Results:Sixty-one relevant publications were identified, of which 17 were related to waning immunity after 2 doses of the vaccine among the general population or healthcare workers, 19 were related to the third or booster dose of vaccination after the second dose among the general population or healthcare workers, and 25 were related to booster dose among immunocompromised patient.Conclusions:Initially, the need for a booster dose was equivocal; however, several studies demonstrated the benefit of the booster dose over time. Adequate scientific information is required regarding the administration of booster doses to the general population as well as the high-risk individuals.

An assessment of the potential impact of the Omicron variant of SARS-CoV-2 in Aotearoa New Zealand.

New Zealand delayed the introduction of the Omicron variant of SARS-CoV-2 into the community by the continued use of strict border controls through to January 2022. This allowed time for vaccination rates to increase and the roll out of third doses of the vaccine (boosters) to begin. It also meant more data on the characteristics of Omicron became available prior to the first cases of community transmission. Here we present a mathematical model of an Omicron epidemic, incorporating the effects of the booster roll out and waning of vaccine-induced immunity, and based on estimates of vaccine effectiveness and disease severity from international data. The model considers differing levels of immunity against infection, severe illness and death, and ignores waning of infection-induced immunity. This model was used to provide an assessment of the potential impact of an Omicron wave in the New Zealand population, which helped inform government preparedness and response. At the time the modelling was carried out, the date of introduction of Omicron into the New Zealand community was unknown. We therefore simulated outbreaks with different start dates, as well as investigating different levels of booster uptake. We found that an outbreak starting on 1 February or 1 March led to a lower health burden than an outbreak starting on 1 January because of increased booster coverage, particularly in older age groups. We also found that outbreaks starting later in the year led to worse health outcomes than an outbreak starting on 1 March. This is because waning immunity in older groups started to outweigh the increased protection from higher booster coverage in younger groups. For an outbreak starting on 1 February and with high booster uptake, the number of occupied hospital beds in the model peaked between 800 and 3,300 depending on assumed transmission rates. We conclude that combining an accelerated booster programme with public health measures to flatten the curve are key to avoid overwhelming the healthcare system.

Mumps in Vaccinated Children and Adolescents

Source: Shepersky L, Marin M, Zhang J, et al. Mumps in vaccinated children and adolescents: 2007–2019. Pediatrics. 2021;148(6): e2021051873; doi.10.1542/peds.2021-051873Investigators from the CDC, Atlanta, GA, conducted a retrospective study to describe the incidence of mumps in children in the US and assess demographic and vaccination characteristics of those with mumps. For the study, they reviewed data in the National Notifiable Diseases Surveillance System (NNDSS) and identified cases of mumps in youths <18 years old in the US between 2007 and 2019. Data from the entire study period were analyzed to characterize pediatric mumps cases by age, state of residence, mumps vaccination status, and whether cases were outbreak-associated. Annual age-specific incidence rates were calculated. A focused analysis was conducted on pediatric mumps cases during the period 2015–2019. In addition to demographic information, data on import status (defined as a case in a child following international travel), parotitis, and complications (orchitis, deafness, meningitis, and encephalitis) were collected. Patients 1-4 years old were classified as up-to-date (UTD) for mumps vaccination if they had received 1 dose of mumps vaccine, and those 5-17 years old were classified as UTD if they had received 2 doses.Between 2007 and 2019, 28,306 mumps cases were reported to NNDSS, including 9,172 (32%) in children. Mumps was reported in all 50 states and the District of Columbia. The annual median number of pediatric mumps cases was 349, with peaks in 2009– 2010 (2,627 pediatric cases) and 2016–2017 (4,093 pediatric cases). Overall, the median annual incidence of mumps in children was 4.7 cases/1,000,000 population. Median annual incidence was 5.8 cases/1,000,000 population in children 5-10 years old and 5.8 cases/1,000,000 population in those 1-4 years of age. During the study period, 64% of pediatric mumps cases with available data were outbreak-associated. Among children with mumps, 89% had ≥1 dose of mumps vaccine.Between 2015 and 2019, 5,461 mumps cases were reported in children. During this period, 54% of pediatric mumps cases occurred in youths 11-17 years old, 33% in those 5-10 years old, 13% in children 1-4 years old, and 1% in infants <1 year old. Only 2% of pediatric cases were associated with international travel. During this period, 74% of children 1-4 years old with mumps and 86% of those 5-17 years old were UTD for mumps vaccination. Among 4,471 cases of pediatric mumps, parotitis was present in 97%. Complications occurred in 75 cases (1%), including orchitis in 2% of boys, deafness in 10 children, meningitis in 3, and encephalitis in 2.The authors conclude that since 2007, 32% of mumps cases in the US occurred in children, most of whom had been vaccinated.Dr Brady has disclosed no financial relationship relevant to this commentary. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.Mumps can occur in fully vaccinated individuals. (See AAP Grand Rounds. 2017;37[6]:64.)1 Two explanations have been suggested for the occurrence of mumps in vaccinated persons: waning of vaccine-induced immunity and antigenic mismatch between the vaccine strain and the circulating wild-type mumps strains.2 Rubin et al3 reported that mumps antibodies declined to near baseline levels 10 years after vaccination for children vaccinated with the second dose at age 4 to 6 years. Additionally, these vaccine-induced antibody responses were lower against the circulating wild-type strains (predominantly genotype G in the US) than against the vaccine strain (genotype A).3-4The current authors noted that 97% of children with mumps presented with parotitis. As prior mumps vaccination does not exclude mumps, diagnostic testing is a consideration when children present with parotitis or mumps complications (eg, orchitis). The preferred test is a buccal swab specimen to detect mumps virus nucleic acid by quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR).5 When buccal swab specimens were collected <2 days after symptom onset, the sensitivity of RT-qPCR was about 83%.1 Therefore, failure to detect mumps virus RNA by RT-qPCR in samples from persons with parotitis does not exclude mumps as a diagnosis. Vaccinated persons may shed small amounts of virus for short periods.5 In previously vaccinated persons who acquire mumps, the mumps-specific immunoglobulin (Ig) M response may be transient, delayed, or not detected.5 Thus, a negative IgM also does not exclude mumps as a diagnosis.With the 2-dose measles-mumps-rubella (MMR) vaccine policy, mumps cases in the US decreased by >99%.6 However, mumps still occurs in vaccinated persons. Parotitis is the hallmark of mumps, and RT-qPCR to detect mumps RNA from a buccal swab specimen is the preferred diagnostic test.A third dose of the current MMR vaccine has been administered during mumps outbreaks.4 A third dose of a mumps vaccine using an alternative mumps strain, however, is a consideration to boost and broaden immunity in vaccine recipients.4

COVID-19 Incidence and Death Rates Among Unvaccinated and Fully Vaccinated Adults with and Without Booster Doses During Periods of Delta and Omicron Variant Emergence - 25 U.S. Jurisdictions, April 4-December 25, 2021.

Previous reports of COVID-19 case, hospitalization, and death rates by vaccination status† indicate that vaccine protection against infection, as well as serious COVID-19 illness for some groups, declined with the emergence of the B.1.617.2 (Delta) variant of SARS-CoV-2, the virus that causes COVID-19, and waning of vaccine-induced immunity (1-4). During August-November 2021, CDC recommended§ additional primary COVID-19 vaccine doses among immunocompromised persons and booster doses among persons aged ≥18 years (5). The SARS-CoV-2 B.1.1.529 (Omicron) variant emerged in the United States during December 2021 (6) and by December 25 accounted for 72% of sequenced lineages (7). To assess the impact of full vaccination with additional and booster doses (booster doses),¶ case and death rates and incidence rate ratios (IRRs) were estimated among unvaccinated and fully vaccinated adults by receipt of booster doses during pre-Delta (April-May 2021), Delta emergence (June 2021), Delta predominance (July-November 2021), and Omicron emergence (December 2021) periods in the United States. During 2021, averaged weekly, age-standardized case IRRs among unvaccinated persons compared with fully vaccinated persons decreased from 13.9 pre-Delta to 8.7 as Delta emerged, and to 5.1 during the period of Delta predominance. During October-November, unvaccinated persons had 13.9 and 53.2 times the risks for infection and COVID-19-associated death, respectively, compared with fully vaccinated persons who received booster doses, and 4.0 and 12.7 times the risks compared with fully vaccinated persons without booster doses. When the Omicron variant emerged during December 2021, case IRRs decreased to 4.9 for fully vaccinated persons with booster doses and 2.8 for those without booster doses, relative to October-November 2021. The highest impact of booster doses against infection and death compared with full vaccination without booster doses was recorded among persons aged 50-64 and ≥65 years. Eligible persons should stay up to date with COVID-19 vaccinations.

Antibody Levels at 3-Years Follow-Up of a Third Dose of Measles-Mumps-Rubella Vaccine in Young Adults.

Mumps outbreaks and breakthrough infections of measles and rubella have raised concerns about waning of vaccine-induced immunity after two doses of measles-mumps-rubella (MMR) vaccination. In the present follow-up study, serum IgG antibodies against mumps, measles and rubella, as well as the functional neutralizing antibodies against both the mumps vaccine strain and mumps outbreak strains were measured longitudinally in young adults that received a third MMR (MMR3) dose. The mumps-specific IgG and virus neutralizing antibody levels at 3 years after vaccination were still elevated compared to pre-vaccination antibody levels, although the differences were smaller than at earlier timepoints. Interestingly, subjects with low antibody levels to mumps before vaccination benefited the most as they showed the strongest antibody increase after an MMR3 dose. Three years after an MMR3 dose, all subjects had antibody levels to measles and rubella above the internationally agreed antibody cutoff levels for clinical protection. Our data support the recommendation that an MMR3 dose may provide additional protection for those that have become susceptible to mumps virus infection during outbreaks. MMR3 also resulted in an increase in anti-measles and rubella antibody levels that lasted longer than might have been expected.

Diphtheria in an Adult: A Paradigm of Waning Immunity

In the past 10 years, there have been several reported cases of the existence of a vaccine-preventable disease from several Indian states. Diphtheria, re-emerge as a major public health problem as this fatal infection used to be noticed in toddlers and school-going has now been stated to occur amongst adults also despite the fully functional Universal Immunisation Program (UIP) in India. India contributed about 53.9% of diphtheria cases globally in the year 2016. In cases, the reason for the upsurge could be attributed to lack of proper immunisation or waning of vaccine-induced immunity with increasing age. Here, a case of a 24-year-old adult male was reported who presented with acute membranous tonsillitis, a preliminary diagnosis made on physical examination. Corynaebacterium diphtheriae was isolated. Finally, the isolate was confirmed as C. diphtheriae using Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS) system.

Determination of ELISA reactive mumps IgG antibodies in MMR vaccine recipients in comparison with MMR vaccine naive children: A cross sectional study

Background/Aim: Mumps is by vaccine preventable infectious disease characterised by parotitis. In India mumps vaccines are not currently used under National Immunisation Programme (NIP). Waning of vaccine-induced immunity is considered to play a central role in the re-emergence of mumps. The comprehensive data on the seroepidemiology of measles, mumps, and rubella (MMR) as well as studies which compare the antibody titre among mumps vaccine naiveand mumps vaccinated children are lacking. The aim of this study was to estimate and compare mumps specific antibody titre in children with and without MMR vaccine. Methods: In 2019/2020, blood samples were collected from 100 healthy children attending immunisation clinic in Government Medical College Kota and associated J K Lon Maternal and Child care hospital Kota. The samples were investigated for MMR IgG antibodies using ELISA. Results: Out of total 100 children included in the study, 32.27 % vaccinated and 4.83 % non-vaccinated children were positive for mumps IgG antibody in the age group of 6 months to 6 years of age. Children aged 6 to 12 years, vaccinated and non-vaccinated, had 31.57 % and 26.57 % positivity, respectively. The seroprevalence of measles, mumps and rubella antibodies among 50 MMR vaccinated children were 94 %, 64 %, and 96 %, respectively. A high measles and rubella seroprevalences were observed among all children age groups, suggesting an effective control program, while the mumps seroprevalence decreased significantly with age. Conclusion: The maximum vaccine effectiveness against mumps for 2 doses of MMR vaccine is ≈ 96 %. The herd immunity threshold to block mumps virus transmission is ≥ 86 %. In this study only 64 % of the vaccinated children were found to have IgG mumps antibodies. In view of morbidity following mumps infection there is a need to incorporate mumps vaccine along with measles and rubella vaccine in the NIP instead of Mr.

A Third Dose of Measles-Mumps-Rubella Vaccine to Improve Immunity Against Mumps in Young Adults.

Waning of vaccine-induced immunity is considered to play a central role in the reemergence of mumps among vaccinated young adults. The aim of the present study was to investigate antibody responses and safety of a third dose of measles-mumps-rubella vaccine (MMR-3) in 150 young adults. Antibody levels were related to a surrogate of protection based on preoutbreak serum antibody levels in 31 persons with and 715 without serological evidence of mumps. Mumps virus-specific immunoglobulin G (IgG) antibody responses and mumps virus-neutralizing antibody responses (based on the focus-reduction neutralizing test) against both the Jeryl Lynn mumps virus vaccine strain (hereafter, the "vaccine strain") and the MuVi/Utrecht.NLD/40.10 outbreak strain (hereafter, the "outbreak strain") were determined, and vaccine safety was evaluated. Four weeks following MMR-3 receipt, levels of IgG, anti-vaccine strain, and anti-outbreak strain antibodies increased by a factor of 1.65, 1.34, and 1.35, respectively. Although antibody levels decreased 1 year later, they were still above the baseline level by a factor of 1.37, 1.15, and 1.27, respectively. Based on the surrogate protective antibody cutoff, significantly more participants were protected against mumps virus infection up to 1 year after vaccination (ie, they had antibody levels above the presumed threshold for herd immunity). MMR-3 receipt increased antibody levels that may protect against mumps virus infection for longer than previously assumed and is expected to be a good and safe intervention for controlling a mumps outbreak. 2016-001104-36; NTR5911.

Effectiveness, immunogenicity and safety of 23-valent pneumococcal polysaccharide vaccine revaccinations in the elderly: a systematic review.

BackgroundIn many industrialized countries routine vaccination with the 23-valent pneumococcal polysaccharide vaccine (PPSV-23) is recommended to prevent pneumococcal disease in the elderly. However, vaccine-induced immunity wanes after a few years, and there are controversies around revaccination with PPSV-23. Here, we systematically assessed the effectiveness and safety of PPSV-23 revaccination.MethodWe conducted a systematic literature review in MEDLINE, EMBASE, and Cochrane Central Register of Controlled Trials from inception to June 2015. We included all study types that compared effectiveness, immunogenicity and/or safety of PPSV-23 as a primary vs. a revaccination dose in persons aged 50 years and older. With respect to immunogenicity, we calculated the ratio of geometric mean antibody concentrations and opsonophagocytic indexes at identical time-points after primary and revaccination. Additionally, we compared rates and severity of adverse events (AEs) after primary and revaccination.ResultsWe included 14 observational studies. 10 studies had a prospective design and analysed data on (i) the same individuals after a first and a second dose of PPSV-23 given 1 to 10 years later (n = 5) or (ii) two groups consisting of participants receiving PPSV-23 who were either vaccine-naïve or had received a first PPSV-23 dose 3 to 13 years earlier (n = 5). Three studies used electronic data bases to compare AEs after primary vs. revaccination doses of PPSV-23 after 1 to 10 years and one study had a cross-sectional design. Number of participants in the non-register-based and register-based studies ranged from 29 to 1414 and 360 to 316,000, respectively. 11 out of 14 included studies were at high risk of bias, three studies had an unclear risk of bias. None of the studies reported data on clinical effectiveness. Immunogenicity studies revealed that during the first two months antibody levels tended to be lower after revaccination as compared to primary vaccination. Thereafter, no obvious differences in antibody levels were observed. Compared to primary vaccination, revaccination was associated with an increased risk of local and systemic AEs, which, however, were usually mild and self-limiting. The risk and severity of AEs appeared to decrease with longer intervals between primary and revaccination.ConclusionData comparing the effectiveness of primary vs. revaccination with PPSV-23 are still lacking, because there are no studies with clinical endpoints. Data from observational studies indicates that revaccination with PPSV-23 is likely to induce long-term antibody levels that are comparable to those after primary vaccination. Given the high disease burden and the waning of vaccine-induced immunity, revaccination with PPSV-23 could be considered in the elderly. The increased risk of local and systemic AEs can likely be mitigated when giving revaccination at least five years after the primary dose. Adequately powered randomized controlled trials using clinical endpoints are urgently needed.Electronic supplementary materialThe online version of this article (doi:10.1186/s12879-016-2040-y) contains supplementary material, which is available to authorized users.

Global threshold dynamics of an SIVS model with waning vaccine-induced immunity and nonlinear incidence

Vaccination is the most effective method of preventing the spread of infectious diseases. For many diseases, vaccine-induced immunity is not life long and the duration of immunity is not always fixed. In this paper, we propose an SIVS model taking the waning of vaccine-induced immunity and general nonlinear incidence into consideration. Our analysis shows that the model exhibits global threshold dynamics in the sense that if the basic reproduction number is less than 1, then the disease-free equilibrium is globally asymptotically stable implying the disease dies out; while if the basic reproduction number is larger than 1, then the endemic equilibrium is globally asymptotically stable indicating that the disease persists. This global threshold result indicates that if the vaccination coverage rate is below a critical value, then the disease always persists and only if the vaccination coverage rate is above the critical value, the disease can be eradicated.

A Cross-Sectional Study on Anti Hepatitis B Immune Status in Vaccinated Healthcare Workers in the West Pomeranian Region of Poland

Hepatitis B vaccination, recommended for medical staff, has a non-response rate of 5% to 32%. In Poland, there is no standardized postvaccination protocol to verify immunity. To determine the fraction of those who have been vaccinated against HBV (with a complete course followed/not followed by a booster) but not checked for serological evidence of hepatitis B immunity and to detect anti-HBs levels in this group by anonymous cross-sectional sero-survey. Surgical/gynecological staff from 16 randomly selected hospitals in West Pomerania, Poland, were surveyed between July 2010-January 2011. EIA system version 3.0 was used to detect anti-HBs. Of 488 participants (439 females, median age 42 years) who were previously vaccinated (1-21 years ago), anti-HBs status was not determined after HBV vaccination in 361 individuals (74.0%; 95% CI: 69.9-77.7%), 5% (18/361) of whom had an anti-HBs titer of 0.0 mIU/ml (12/18 who were given booster doses developed anti-HBs > 10 mIU/ml) and 7.2% (26/361) of whom had an anti-HBs titer of 0.1-10 mIU/ml. The multivariate logistic regression model revealed that working in a teaching hospital was associated with lower odds of not being checked for anti-HBs after HBV vaccination (OR 0.22, 95% CI: 0.14-0.35; P = 0.0001). The lack of a strict post-HBV vaccination policy to confirm immunity results in the majority of surgical/gynecological staff not checking their anti-HBs levels after HBV immunization. It is unknown whether the absence of current serological evidence of hepatitis B immunity can be attributed to non-response, the waning of vaccine-induced immunity, or preserved anamnestic response. The lack of a booster vaccination response in a fraction of subjects suggests that they are non-responders. Strict post-vaccination testing to document immunity remains the key practice to detect non-responders among medical staff.

Persistence of long-term immunity to hepatitis B among adolescents immunized at birth

The long-term duration of recombinant hepatitis B vaccine-induced immunity among persons vaccinated starting at birth is still not well understood. Waning of vaccine-induced immunity could leave young adults at risk of hepatitis B virus infection due to behavioral or occupational exposures. We followed a cohort of children immunized starting at birth with a 3-dose regimen of recombinant hepatitis B vaccine (5 mcg, 2.5 mcg, 2.5 mcg). They were challenged with a booster dose of the hepatitis B vaccine 10 and 15 years after vaccination to assess anamnestic response as a measure of persistence of protection. Among 108 participants who had lost protective antibody levels against hepatitis B, the majority (>70%) had an anamnestic response to the booster dose; response rates did not decline significantly between 10 and 15 years follow-up periods. A high antibody concentration following primary vaccination was independently associated with an anamnestic response later on in life. Nonetheless, ~20-30% of participants were unable to mount an immune response after boosting. Hepatitis B revaccination might be required for persons vaccinated starting at birth if opportunities for hepatitis B virus exposure exist. Future vaccine recommendations should be based on studies ascertaining protection against clinically significant disease.

Measles serological survey in the Italian population: Interpretation of results using mixture model

In 2003–2004, a national measles seroprevalence study was conducted in Italy and data were analysed by using both commercial ELISA cut-off, and by applying a mixture model. Results of the two methods were compared and interpreted in the light of measles incidence, vaccination coverage and previous seroprevalence data. Seroprevalence rates observed in 2004 were similar to those observed in a previous study conducted in 1996 for children up to 9 years of age, while they were significantly lower in individuals aged 10–19 years. Mixture model approach allowed to better understand these results, suggesting that in these latter age groups there was a waning of vaccine-induced immunity mainly in Northern-Central regions which historically had the highest vaccination coverage.

Pertussis: increasing disease as a consequence of reducing transmission

Since the 1980s, the occurrence of pertussis cases in developed countries has increased and shifted towards older age groups. This resurgence follows 30 years of intense mass vaccination, and has been attributed primarily to three factors: (1) more effective diagnosis of the disease, (2) waning of vaccine-induced immunity, and (3) loss of vaccine efficacy due to the emergence of new Bordetella pertussis strains. Here we develop and analyse a mathematical model to assess the plausibility of these hypotheses. We consider that exposure to B pertussis through natural infection or vaccination induces an immune response that prevents severe disease but does not fully prevent mild infections. We also assume that these protective effects are temporary due to waning of immunity. These assumptions, describing the mode of action of adaptive immunity, are combined with a standard transmission model. Two distinct epidemiological scenarios are detected: under low transmission, most infections lead to severe disease; under high transmission, mild infections are frequent, boosting clinical immunity and maintaining low levels of severe disease. The two behaviours are separated by a reinfection threshold in transmission. As a result, the highest incidence of severe disease is expected to occur at intermediate transmission intensities--near the reinfection threshold--suggesting that pertussis resurgence may be induced by a reduction in transmission, independently of vaccination. The model is extended to interpret the outcomes of current control measures and explore scenarios for future interventions.

Duration of Immunity Against Pertussis After Natural Infection or Vaccination

Despite decades of high vaccination coverage, pertussis has remained endemic and reemerged as a public health problem in many countries in the past 2 decades. Waning of vaccine-induced immunity has been cited as one of the reasons for the observed epidemiologic trend. A review of the published data on duration of immunity reveals estimates that infection-acquired immunity against pertussis disease wanes after 4-20 years and protective immunity after vaccination wanes after 4-12 years. Further research into the rate of waning of vaccine-acquired immunity will help determine the optimal timing and frequency of booster immunizations and their role in pertussis control.

Emerging diseases: measles.

High vaccination coverage rates and the administration of a second dose of measles vaccine have resulted in a significant decline in the incidence of measles and neurologic diseases due to measles in many countries. However, intermittent outbreaks of measles still occur even in countries with excellent vaccination coverage, suggesting the existence of high rates of measles virus introduction from endemic regions and/or waning of vaccine-induced immunity. Strategies to sustain high levels of global immunity to measles virus by increasing vaccine coverage with routine and supplementary vaccination campaigns must be supported.