Routine Vaccination Services Research Articles

Multiple cohort HPV vaccination in Zimbabwe: 2018–2019 program feasibility, awareness, and acceptability among health, education, and community stakeholders

IntroductionZimbabwe introduced human papillomavirus (HPV) vaccine nationally in May 2018, targeting multiple cohorts (girls aged 10–14 years) through a school-based vaccination campaign. One year later, the second dose was administered to the multiple cohorts concurrently with the first dose given to a new single cohort of girls in grade 5. We conducted cross-sectional surveys among health workers, school personnel, and community members to assess feasibility of implementation, training, social mobilization, and community acceptability. MethodsThirty districts were selected proportional to the volume of the HPV vaccine doses delivered in 2018; two health facilities were randomly selected within each district. One health worker, school health coordinator, village health worker, and community leader were surveyed at each selected health facility and surrounding area during January-February 2020, using standard questionnaires. Descriptive analysis was completed across groups. ResultsThere were 221 interviews completed. Over 60% of health workers reported having enough staff to carry out vaccination sessions in schools while maintaining routine vaccination services in health facilities. All school health coordinators felt the HPV vaccine should be delivered in schools in the future. Knowledge of the correct target cohort eligibility decreased from 91% in 2018 to 50% in 2020 among health workers. Understanding of HPV infection and use of HPV vaccine for cervical cancer prevention was above 90% for all respondents. Forty-two percent of respondents reported hearing rumors about the HPV vaccine, primarily regarding infertility and safety. ConclusionsFindings demonstrate the presence of highly knowledgeable staff at health facilities and schools, strong community acceptance, and a school-based HPV program considered feasible to implement in Zimbabwe. However, misunderstandings regarding target eligibility and rumors persist, which can impact vaccine uptake and coverage. Continued social mobilization efforts to maintain community demand and training on eligibility were recommended. Integration, partnerships, and resource mobilization are also needed to ensure program sustainability.

Will COVID-19 Lead to a Resurgence of Vaccine-Preventable Diseases?

The outbreak of coronavirus disease (COVID-19) has been affecting various sectors, including regular health services negatively. Vaccination, which saves the lives of 2–3 million populations of different age groups every year, is one of the most affected services by COVID-19. The routine vaccination services and outreach programs have been halted owing to lockdowns imposed on account of escalated cases of COVID-19 all over the world, affecting millions of lives at the stake of vaccine-preventable disease (VPD) henceforth. However, as it is becoming evident that we will have to live with COVID-19 for some time and many countries have lifted the lockdown, vaccination programs and campaigns have resumed with stringent preventive measures to be followed for COVID-19. These programs and campaigns have been trying to overlook and provide the missed vaccination during the imposed lockdown period and continue the other vaccination services to the public in the best possible ways. The collaborative approaches of various health-related organisations, governments and the healthcare workers are necessary to deliver the routine and mass vaccination services in an improvised manner.

Pertussis outbreak in southern Ethiopia: challenges of detection, management, and response

BackgroundDespite the availability of effective vaccines, pertussis remains endemic with high fatality rates in low and middle-income countries (LMIC). This study aims to describe an outbreak of pertussis in a health district of Ethiopia. The study highlights the challenges faced by the health system in identifying pertussis cases and appropriately responding to the outbreak at the district level.MethodsA descriptive cross-sectional study was conducted using data sourced from the District Public Health Emergency and Management (PHEM) surveillance service and outbreak management field reports. Stratified attack rates and fatality rates for pertussis are described. Systemic problems leading to the outbreak are explored and narrated. A modified CDC pertussis case definition was employed with a polymerase chain reaction used to confirm cases.ResultsFrom September 2018 to January 2019, 1840 suspected, probable, and confirmed pertussis cases and six deaths were identified. Pertussis cases ranged from 1 month to 51 years in age. An outbreak occurred in 14 out of the 24 villages of Dara Malo district. The overall attack rate was 1708 per 100,000 population with a fatality rate of 3.3 per 1000 pertussis cases. The highest attack rate of 12,689/100,000 was seen in infants. Among confirmed, probable and suspected pertussis cases, only 41.1% had completed the three-dose pertussis vaccine’s primary schedule. The household survey revealed a population coverage of 73.4 and 40.8% for Pentavalent vaccine dose one and three respectively. Investigations suggested the existence of a poor cold chain management system in the study area.ConclusionsThere is an urgent need to build capacity to strengthen routine vaccination services and improve the maintenance of the vaccine cold chain. Other LMICs are urged to take lessons learned from this outbreak to strengthen their own vaccination programs and capacitate health workers to manage local outbreaks.

Reasons for non-vaccination and incomplete vaccinations among children in Pakistan

BackgroundGlobal immunization efforts have received a boost through the introduction of several new vaccines. These efforts however, are threatened by sub-optimal vaccine coverage, particularly in countries with large birth cohorts. Pakistan has one of the largest birth cohorts in the world, where coverage of routine vaccination remains persistently inadequate. We undertook this study to ascertain reasons for non-vaccination or incomplete vaccination of children less than two years in 8 districts of southern Pakistan. MethodsA cross-sectional survey using WHO recommended rapid coverage assessment technique was conducted in 2014. Using probability proportional to size method, we sampled 8400 households with eligible children (aged 4–12 months). Using a structured questionnaire, mothers or other primary caregivers were interviewed to determine vaccination status of an index child. In case of non-vaccination or incomplete vaccination, respondents were asked for reasons leading to low/no vaccine uptake. ResultsBased on both vaccination record and recall, only 30.8% of children were fully vaccinated, 46% had an incomplete vaccination status while 23%were non-vaccinated. The most frequently reported reasons for non-vaccination included: mothers/caregivers being unaware of the need for vaccination (35.3%), a fear of side effects (23%), mother/caregiver being too busy (16.6%), distance from vaccination centers (13.8%), and non-availability of either vaccinators or vaccines at vaccination centers (10.7%). Reasons identified for incomplete vaccination were similar, with caregivers being unaware of the need for subsequent doses (27.3%), non-availability of vaccinators or vaccines (17.7%), mother/caregiver being too busy (14.8%), fear of side effects (11.2%), and postponement for another time (8.7%). ConclusionVarious factors result in non-compliance with vaccination schedules and vaccine refusal within the surveyed communities, ranging from lack of knowledge to non-availability of supplies at vaccination centers. These barriers are best addressed through multi-pronged strategies addressing supply gaps, increasing community awareness and enhancing demand for routine vaccination services.

Predictors of measles vaccination coverage among children 6–59 months of age in the Democratic Republic of the Congo

BackgroundMeasles is a significant contributor to child mortality in the Democratic Republic of the Congo (DRC), despite routine immunization programs and supplementary immunization activities (SIA). Further, national immunization coverage levels may hide disparities among certain groups of children, making effective measles control even more challenging. This study describes measles vaccination coverage and reporting methods and identifies predictors of vaccination among children participating in the 2013–2014 DRC Demographic and Health Survey (DHS). MethodsWe examined vaccination coverage of 6947 children aged 6–59 months. A multivariate logistic regression model was used to identify predictors of vaccination among children reporting vaccination via dated card in order to identify least reached children. We also assessed spatial distribution of vaccination report type by rural versus urban residence. ResultsUrban children with educated mothers were more likely to be vaccinated (OR = 4.1, 95% CI: 1.6, 10.7) versus children of mothers with no education, as were children in wealthier rural families (OR = 2.9, 95% CI: 1.9, 4.4). At the provincial level, urban areas more frequently reported vaccination via dated card than rural areas. ConclusionsResults indicate that, while the overall coverage level of 70% is too low, socioeconomic and geographic disparities also exist which could make some children even less likely to be vaccinated. Dated records of measles vaccination must be increased, and groups of children with the greatest need should be targeted. As access to routine vaccination services is limited in DRC, identifying and targeting under-reached children should be a strategic means of increasing country-wide effective measles control.

Challenges in Estimating Vaccine Coverage in Refugee and Displaced Populations: Results From Household Surveys in Jordan and Lebanon.

Ensuring the sustained immunization of displaced persons is a key objective in humanitarian emergencies. Typically, humanitarian actors measure coverage of single vaccines following an immunization campaign; few measure routine coverage of all vaccines. We undertook household surveys of Syrian refugees in Jordan and Lebanon, outside of camps, using a mix of random and respondent-driven sampling, to measure coverage of all vaccinations included in the host country’s vaccine schedule. We analyzed the results with a critical eye to data limitations and implications for similar studies. Among households with a child aged 12–23 months, 55.1% of respondents in Jordan and 46.6% in Lebanon were able to produce the child’s EPI card. Only 24.5% of Syrian refugee children in Jordan and 12.5% in Lebanon were fully immunized through routine vaccination services (having received from non-campaign sources: measles, polio 1–3, and DPT 1–3 in Jordan and Lebanon, and BCG in Jordan). Respondents in Jordan (33.5%) and Lebanon (40.1%) reported difficulties obtaining child vaccinations. Our estimated immunization rates were lower than expected and raise serious concerns about gaps in vaccine coverage among Syrian refugees. Although our estimates likely under-represent true coverage, given the additional benefit of campaigns (not captured in our surveys), there is a clear need to increase awareness, accessibility, and uptake of immunization services. Current methods to measure vaccine coverage in refugee and displaced populations have limitations. To better understand health needs in such groups, we need research on: validity of recall methods, links between campaigns and routine immunization programs, and improved sampling of hard-to-reach populations.

Estimation of child vaccination coverage at state and national levels in India.

ObjectiveTo review the data, for 1999–2013, on state-level child vaccination coverage in India and provide estimates of coverage at state and national levels.MethodsWe collated data from administrative reports, population-based surveys and other sources and used them to produce annual estimates of vaccination coverage. We investigated bacille Calmette–Guérin vaccine, the first and third doses of vaccine against diphtheria, tetanus and pertussis, the third dose of oral polio vaccine and the first dose of vaccine against measles. We obtained relevant data covering the period 1999–2013 for each of 16 states and territories and the period 2001–2013 for the state of Jharkhand – which was only created in 2000. We aggregated the resultant state-level estimates, using a population-weighted approach, to give national values.FindingsFor each of the vaccinations we investigated, about half of the 253 estimates of annual coverage at state level that we produced were based on survey results. The rest were based on interpolation between – or extrapolation from – so-called anchor points or, more rarely, on administrative data. Our national estimates indicated that, for each of the vaccines we investigated, coverage gradually increased between 1999 and 2010 but then levelled off.ConclusionThe delivery of routine vaccination services to Indian children appears to have improved between 1999 and 2013. There remains considerable scope to improve the recording and reporting of childhood vaccination coverage in India and regular systematic reviews of the coverage data are recommended.

Reducing routine vaccination dropout rates: evaluating two interventions in three Kenyan districts, 2014.

BackgroundGlobally, vaccine preventable diseases are responsible for nearly 20 % of deaths annually among children <5 years old. Worldwide, many children dropout from the vaccination program, are vaccinated late, or incompletely vaccinated. We evaluated the impact of text messaging and sticker reminders to reduce dropouts from the vaccination program.MethodsThe evaluation was conducted in three selected districts in Kenya: Machakos, Langata and Njoro. Three health facilities were selected in each district, and randomly allocated to send text messages or provide stickers reminding parents to bring their children for second and third dose of pentavalent vaccine, or to the control group (routine reminder) with next appointment date indicated on the well-child booklet. Children aged <12 months presenting for their first dose of pentavalent vaccine were enrolled. A dropout was defined as not returning for vaccination ≥2 weeks after scheduled date for third dose of pentavalent vaccine. We calculated dropout rate as a percentage of the difference between first and third pentavalent dose.ResultsWe enrolled 1,116 children; 372 in each intervention and 372 controls between February and October 2014. Median age was 45 days old (range: 31–99 days), and 574 (51 %) were male. There were 136 (12 %) dropouts. Thirteen (4 %) children dropped out among those who received text messages, 60 (16 %) among who received sticker reminders, and 63 (17 %) among the controls. Having a caregiver with below secondary education [Odds Ratio (OR) 1.8, 95 % Confidence Interval (CI) 1.1–3.2], and residing >5 km from health facility (OR 1.6, CI 1.0–2.7) were associated with higher odds of dropping out. Those who received text messages were less likely to drop out compared to controls (OR 0.2, CI 0.04–0.8). There was no statistical difference between those who received stickers and controls (OR 0.9, CI 0.5–1.6).ConclusionText message reminders can reduce vaccination dropout rates in Kenya. We recommend the extended implementation of text message reminders in routine vaccination services.

Reply to Thysen et al

To the Editor—We thank Thysen et al for their cautionary perspective on BCG vaccination policy changes. Although we found improved immunogenicity of BCG vaccine in human immunodeficiency virus (HIV)–exposed infants vaccinated at 8 weeks of age, compared with immunogenicity among those vaccinated at birth [1], we do not recommend changes to vaccine-delivery services on the basis of these data. Nonetheless, our study contributes valuable data indicating that the immunogenicity of BCG vaccination is not negatively affected by delaying administration until 8 weeks of age, which is much needed in regions of high HIV prevalence where new tuberculosis vaccination strategies are undergoing clinical evaluation [2]. As highlighted by Thysen et al, previous trials have shown that BCG vaccination can improve all-cause mortality in West African children [3, 4], and in some cases, can improve innate and adaptive immunity to unrelated antigens [5, 6]. However, it is important to note the context in which these studies were performed. Gambia and Guinea-Bissau have poor healthcare infrastructures, high infant mortality [7], and considerably lower HIV infection and tuberculosis incidences than South Africa, where our trial was conducted. In such settings, the benefits associated with early BCG vaccination could outweigh any risks posed to HIV-infected infants, and delaying BCG vaccination could be detrimental to child survival. In settings with good integration of routine infant vaccination services, programs to prevent and treat tuberculosis, and services to prevent mother-to-child transmission of HIV, where infrastructure could support selectively delayed BCG vaccination for HIV-exposed infants, the risks due to delaying BCG vaccination would be lower. Additional points to consider are that in the prior studies from Guinea-Bissau, BCG vaccination was combined with other interventions, including vitamin A administration, and the randomized trials studied delayed BCG vaccination in low-birth-weight infants only, in whom mortality is high and immunity less mature [3, 4]. In West Africa, routine infant immunization coverage is relatively low, and data on the causes of infant mortality in these studies are limited [8]. A recent systematic review of studies performed elsewhere did not show any clear evidence of beneficial nonspecific effects associated with BCG vaccination [9], which may be setting specific. Furthermore, it is unclear whether there are any nonspecific protective effects from BCG vaccination in HIV-exposed infants, who have altered adaptive and innate immunity [10, 11]. One of the suggested mechanisms by which BCG vaccination improves immunity to pathogens other than the agents of tuberculosis is through monocyte reprogramming [5]. Monocyte responsiveness in HIV-exposed infants appears to be higher than that in unexposed infants, potentially implying differential epigenetics in this population [12]. In our randomized controlled trial in HIV-exposed infants [1], there were 2 deaths (mortality rate, 1.3%), both in infants who received BCG vaccine at birth and were not infected with HIV. In a recent randomized controlled trial of delayed BCG vaccination until 14 weeks of age in Khayelitsha, South Africa, we likewise found no difference in mortality between HIV-exposed infants receiving delayed BCG vaccination versus those vaccinated at birth [13]. All tuberculosis cases occurred between week 20 and month 18 of age; no investigations for tuberculosis were completed prior to 14 weeks of age. Therefore, in neither of these 2 South African studies did any infants receive a tuberculosis diagnosis before 14 weeks of age. Thysen et al have not considered additional important complications of live BCG vaccination in HIV-infected infants apart from disseminated BCG, which is a rare complication. BCG adenitis, often occurring in the context of immune reconstitution inflammatory syndrome, occurs in 6.6% of infected infants, even in the setting of very early initiation of antiretroviral therapy [14]. The true number of BCG vaccine–associated adverse events in HIV-infected infants is likely higher, given limited surveillance, and would again be setting specific. Finally, BCG vaccination leads to nonspecific CD4+ T-cell activation in HIV-exposed infants, potentially making them more susceptible to HIV infection or disease progression if HIV infected [15]. All of these factors should be considered when implementing selectively delayed BCG vaccinations strategies in HIV-exposed infants. We recommend that BCG vaccination strategies in research and routine care settings consider local factors, including the prevalence of HIV, the prevalence of tuberculosis, the healthcare infrastructure, and key indicators such as infant mortality rates. Further research is needed on BCG vaccination's risks and benefits in HIV-exposed infants before improved tuberculosis preventive vaccines are introduced.

Overview of global, regional, and national routine vaccination coverage trends and growth patterns from 1980 to 2009: implications for vaccine-preventable disease eradication and elimination initiatives.

Review of the historical growth in annual vaccination coverage across countries and regions can better inform decision makers' development of future goals and strategies to improve routine vaccination services. Using the World Health Organization (WHO) and the United Nations Children's Fund estimates of annual national third dose of diphtheria-tetanus-pertussis-containing vaccine (DTP3) and third dose of polio vaccine (POL3) coverage for 1980-2009, we calculated the mean absolute annual rate of change in national DTP3 coverage among all countries (globally) and among countries within each WHO region, as well as the number of years taken by each region to reach specific regional coverage levels. Last, we assessed differences in mean absolute annual rate of change in DTP3 coverage, stratified by baseline level of DTP3 coverage. During the 1980s, global DTP3 coverage increased a mean of 5.3 percentage points/year. Annual rate of change decreased to 0.5 percentage points/year in the 1990s and then increased to 0.9 percentage points/year during the 2000s. Mean annual rate of change in coverage across all countries was highest (9.2 percentage points) when national coverage levels were 26%-30% and lowest (-0.9 percentage points) when national coverage levels were 96%-100%. Regional differences existed as both WHO South-East Asia Region and WHO African Region countries experienced mean negative DTP3 coverage growth at lower coverage levels (81%-85%) than other regions. The regions that have achieved 95% DTP3 coverage (Americas, Western Pacific, and European) took 25-29 years to reach that level from a level of 50% DTP3 coverage. POL3 coverage change trends were similar to described DTP3 coverage change trends. Mean national coverage growth patterns across all regions are nonlinear as coverage levels increase. Saturation points of mean 0 percentage-point growth in annual coverage varies by region and require further investigation. The achievement of >90% routine coverage is observed to take decades, which has implications for disease eradication and elimination initiatives.

Meningococcal vaccine introduction in Mali through mass campaigns and its impact on the health system.

To evaluate the impact of the meningococcal A (MenA) vaccine introduction in Mali through mass campaigns on the routine immunization program and the wider health system. We used a mixed-methods case-study design, combining semi-structured interviews with 31 key informants, a survey among 18 health facilities, and analysis of routine health facility data on number of routine vaccinations and antenatal consultations before, during, and after the MenA vaccine campaign in December 2010. Survey and interview data were collected at the national level and in 2 regions in July and August 2011, with additional interviews in January 2012. Many health system functions were not affected-either positively or negatively-by the MenA vaccine introduction. The majority of effects were felt on the immunization program. Benefits included strengthened communication and social mobilization, surveillance, and provider skills. Drawbacks included the interruption of routine vaccination services in the majority of health facilities surveyed (67%). The average daily number of children receiving routine vaccinations was 79% to 87% lower during the 10-day campaign period than during other periods of the month. Antenatal care consultations were also reduced during the campaign period by 10% to 15%. Key informants argued that, with an average of 14 campaigns per year, mass campaigns would have a substantial cumulative negative effect on routine health services. Many also argued that the MenA campaign missed potential opportunities for health systems strengthening because integration with other health services was lacking. The MenA vaccine introduction interrupted routine vaccination and other health services. When introducing a new vaccine through a campaign, coverage of routine health services should be monitored alongside campaign vaccine coverage to highlight where and how long services are disrupted and to mitigate risks to routine services.

Effektivität, Populationseffekte und Gesundheitsökonomie der Impfungen gegen Masern und Röteln

Vaccination against measles and rubella has been included in national immunization programs worldwide for several decades. In this article, we present the evidence related to the effectiveness of measles and rubella vaccination based on published systematic reviews, and we describe the epidemiological and health economic effects of vaccination at a population level. Several observational studies demonstrate the high effectiveness (> 90 %) of both measles and rubella vaccination. The global measles mortality reduction and the dramatic decrease in rubella and measles incidences after introduction of routine immunization contribute to the very high quality of evidence. The countries of the Americas have proved that it is feasible to eliminate measles and rubella by strengthening infant immunization through routine vaccination services and by conducting supplemental immunization activities in other childhood age groups so as to close immunity gaps. An economic evaluation of measles and rubella vaccination specifically for the healthcare system in Germany does not exist. However, we conducted a systematic review and identified 11 health-economic studies from other industrialized countries and one for a hypothetical industrialized country. Results indicate that vaccination against measles and rubella had either a cost-effective or even a cost-saving potential, which could be assumed with some limitations also for the German setting. In conclusion, there is compelling evidence that the available vaccines are very effective and that measles and rubella elimination is feasible if adequate vaccination strategies are implemented. In Germany, catch-up vaccination programs are urgently needed for children, adolescents, and young adults specifically in the western federal states.

Global eradication of measles: A highly contagious and vaccine preventable disease-what went wrong in Africa?

This review study reports on global eradication of measles: a highly contagious and vaccine preventable disease-what went wrong in its eradication in Africa. Measles is one of the most contagious human diseases which have continued to cause large outbreaks all over the world even in countries that have achieved high vaccination coverage with a single dose strategy. The disease can also lead to lifelong disabilities including brain damage, blindness, and deafness. These serious complications are rare in developed countries where measles vaccine is widely available, the highest mortality is however found in poor nations. The disease has remained the fifth leading cause of deaths among children less than five years of age, worldwide. It accounts for 44% of total deaths due to vaccine preventable diseases (VPD), among children less than 15 years, the highest mortality occurring in poor communities with malnutrition, overcrowding and low vaccination coverage. Indeed, measles transmission has been interrupted in several countries, reinforcing the view that measles eradication is technically feasible using existing vaccines and intervention strategies. However, measles still accounts for 10% of global mortality from all causes among children aged <5 years (i.e., approximately 1 million deaths annually). Progress toward measles control varies substantially among countries and regions. In Nigeria where there is perennial, low routine vaccination coverage and where the quality of the mass immunization campaign is not high enough, large and persistent measles outbreaks continue to occur with high morbidity and mortality. Today, despite the availability of a safe, effective and relatively inexpensive vaccine for more than 40 years, measles still kills more than any other vaccines preventable disease among children. There is therefore, the urgent need to revisit the measles immunization and vaccination programme in Africa and in our country Nigeria with the sole aim of introducing a two-dose schedule to halt the endemic transmission. This is believed to bring about the successful eradication of measles in Africa. Intensified efforts will be necessary to implement appropriate control and elimination strategies, including supplementary vaccination campaigns, expansion of routine vaccination services, and surveillance. These strategies and estimates of the resources will also be required to implement them will require adjustment based on accumulating experience. Programmatic and financial obstacles must be overcome if the final goal of measles eradication is to be achieved. Key words: Epidemiology; highly contagious disease, immunization, immunosuppression public health; vaccination, vaccine preventable disease, measles, measles virus, measles vaccine

The role of vaccines in elimination and global eradication of measles: A review of literature

This review summarizes the role of vaccines in elimination and global eradication of measles-a review of literature. Measles eradication is defined as the interruption of measles transmission worldwide as a result of deliberate efforts; intervention methods may no longer be needed. It represents the sum of successful elimination efforts in all countries. Indeed, measles transmission has been interrupted in several countries, reinforcing the view that measles eradication is technically feasible using existing vaccines, laboratory techniques and intervention strategies. However, measles still accounts for 10% of global mortality from all causes among children aged less than 5 years (That is, approximately 1 million deaths annually). Vaccination proper coverage is key indicator of campaign success and to predict control on measles. In Nigeria where there is perennial, low routine vaccination coverage and where the quality of the mass immunization campaign is not high enough, large and persistent measles outbreaks continue to occur with high morbidity and mortality. Immunization and vaccination remains one of the most cost effective strategies to prevent infectious diseases. However, the most effective and efficient way to protect the health of children is by immunization before the risk of disease arises. Vaccination has succeeded in eradicating small pox in the world, soon would be achieved with polio and measles will be next to reach the same degree of disease control (viz, worldwide eradication) as has occurred with smallpox. The efficacy of vaccination and immunization in reducing the incidences of several diseases is clearly shown by the success story of measles control in developed countries of the world. However, intensified efforts are necessary to implement appropriate control and elimination strategies, including supplementary vaccination campaigns, expansion of routine vaccination services, and surveillance. Key words: Antibody, elimination, eradication, immunization, measles, measles virus, measles vaccine, vaccination.

Measles: a disease that has to be eradicated.

The incidence of measles is on the decline but it still claims the lives of one million children annually worldwide. The devastating effects of the disease on the health and nutrition of children in developing countries and its high mortality are well documented. The rapid decay of maternal antibodies in infants in developing countries results in early susceptibility to the disease and hence the general recommendation to vaccinate at the age of 9 months. Sustained international efforts have raised global vaccination coverage rates to around 80% at which level it has remained static. Many countries in the western hemisphere have eliminated the disease by adopting aggressive strategies, which include one-off 'catch-up' mass campaigns to vaccinate all children aged 1-14 years, 'mop-up' campaigns targeting children who were missed during the 'catch-up' campaign, efficient routine vaccination services capable of reaching 90% of infants, strong surveillance activities, prompt outbreak response, and 'follow-up' campaigns every 2-4 years which target 1-4-year-old children. This success story coupled with the fact that measles has many biological features favouring eradication, and considering that it is a severe and lethal disease still prevailing in many areas, calls for immediate international adoption of eradication goals within a specified period of time.

Measles elimination in the Americas. Evolving strategies.

The strategy currently used to control measles in most countries has been to immunize each successive birth cohort through the routine health services delivery system. While measles vaccine coverage has increased markedly, significant measles outbreaks have continued to recur. During the past 5 years, experience in the Americas suggests that measles transmission has been interrupted in a number of countries (Cuba, Chile, and countries in the English-speaking Caribbean and successfully controlled in all remaining countries. Since 1991 these countries have implemented one-time "catch-up" vaccination campaigns (conducted during a short period, usually 1 week to 1 month, and targeting all children 9 months through 14 years of age, regardless of previous vaccination status or measles disease history). These campaigns have been followed by improvements in routine vaccination services and in surveillance systems, so that the progress of the measles elimination efforts can be sustained and monitored. Follow-up mass vaccination campaigns for children younger than 5 years are planned to take place every 3 to 5 years.