2-dose Vaccination Coverage Research Articles

The impact of a prolonged ebola outbreak on measles elimination activities in Guinea, Liberia and Sierra Leone, 2014-2015.

IntroductionGuinea, Sierra Leone and Liberia have attained significant reduction in measles incidence between 2004 and 2013. The Ebola outbreak in 2014-2015 in West Africa caused significant disruption of the health service delivery in the three worst affected countries. The magnitude of the impact on the immunization program has not been well documented.MethodsWe reviewed national routine immunization administrative coverage data as well as measles surveillance performance and measles epidemiology in the years before, during and after the EVD outbreak in Guinea, Liberia, Sierra Leone.ResultsBoth Liberia and Guinea experienced a sharp decline of more than 25% in the monthly number of children vaccinated against measles in 2014 and 2015 as compared to the previous years, while there was no reported decline in Sierra Leone. Guinea and Liberia experienced a decline in measles surveillance activity and performance indicators in 2014 and 2015. During this period, there was an increase in measles incidence and a decline in the mean age of measles cases reported in Liberia and Sierra Leone. Guinea started reporting high measles incidence in 2016. All three countries organized measles supplemental immunization activities by June 2015. Liberia achieved 99% administrative coverage, while Guinea and Sierra Leone attained 90.6% and 97.2% coverage respectively. There were no severe adverse events reported during these mass vaccination activities. The disruptive effect of the Ebola outbreak on immunization services was especially evident in Guinea and Liberia. Our review of the reported administrative vaccination coverage at national level does not show significant decline in measles first dose vaccination coverage in Sierra Leone as compared to other reports. This may be due to inaccuracies in coverage monitoring and data quality problems. The increases in measles transmission and incidence in these three countries can be explained by the rapid accumulation of susceptible children. Despite the organization of mass vaccination activities, measles incidence through 2017 has remained higher than the pre-Ebola period in all three countries.ConclusionThe Ebola outbreak in West Africa significantly affected measles vaccination coverage rates in two of the three worst affected countries, and led to persistent gaps in coverage, along with high measles incidence that was documented until two years after the end of the Ebola outbreak. Liberia and Sierra Leone have demonstrated coverage improvements after the end of the Ebola outbreak.

An Outbreak of Measles in a University in Korea, 2014.

Measles has been declared eliminated from the Korea since 2006. In April 2014, a measles outbreak occurred at a University in Seoul. A total of 85 measles cases were identified. In order to estimate vaccine effectiveness of measles vaccine, we reviewed the vaccination records of the university students. The vaccine effectiveness of two doses of measles containing vaccine was 60.0% (95% CI, 38.2–74.1; P < 0.05). Transmission was interrupted after the introduction of outbreak-response immunization. The outbreak shows that pockets of under-immunity among college students may have facilitated the disease transmission despite the high 2-dose vaccination coverage in the community.

Progress Toward Eliminating Hepatitis A Disease in the United States.

Hepatitis A virus (HAV) disease disproportionately affects adolescents and young adults, American Indian/Alaska Native and Hispanic racial/ethnic groups, and disadvantaged populations. During 1996-2006, the Advisory Committee on Immunization Practices (ACIP) made incremental changes in hepatitis A (HepA) vaccination recommendations to increase coverage for children and persons at high risk for HAV infection. This report examines the temporal association of ACIP-recommended HepA vaccination and disparities (on the absolute scale) in cases of HAV disease and on seroprevalence of HAV-related protection (measured as antibody to HAV [anti-HAV]). ACIP-recommended childhood HepA vaccination in the United States has eliminated most absolute disparities in HAV disease by age, race/ethnicity, and geographic area with relatively modest ≥1-dose and ≥2-dose vaccine coverage. However, the increasing proportion of cases of HAV disease among adults with identified and unidentified sources of exposure underscores the importance of considering new strategies for preventing HAV infection among U.S. adults. For continued progress to be made toward elimination of HAV disease in the United States, additional strategies are needed to prevent HAV infection among an emerging population of susceptible adults. Notably, HAV infection remains endemic in much of the world, contributing to U.S. cases through international travel and the global food economy.

The independent impact of newborn hepatitis B vaccination on reducing HBV prevalence in China, 1992–2006: A mathematical model analysis

ObjectiveTo evaluate the independent impact of newborn hepatitis B vaccination on reducing HBV prevalence in China, from its introduction in 1992 to 2006. MethodsAn age- and time-dependent discrete dynamic model was developed to simulate HBV transmission in China under the assumptions of no any change in interventions and only with newborn vaccination introduction, respectively. The initial conditions of the model were determined according to the national serosurvey in 1992. The simulated results were compared with the observed results of the national serosurvey in 2006, and the contribution rate of newborn vaccination on reducing HBV prevalence was calculated overall and by birth cohort. ResultsThe total HBV prevalence would remain stable through the 14-year period if no any change in interventions, but decrease year by year if only with newborn vaccination introduction. Newborn vaccination could account for more than 50% of the reduction of the total HBV prevalence, although the full 3-dose and timely birth dose vaccination coverage rates were low in the early years. The results by birth cohort showed that the higher the two coverage rates, the higher contribution rate on reducing HBV prevalence. For the 2005 birth cohort which had high levels in the two coverage rates, the contribution rate could reach more than 95%. ConclusionNewborn hepatitis B vaccination from 1992 to 2006 in China had played the most important role in reducing HBV prevalence. Newborn vaccination with high full 3-dose and timely birth dose coverage rates is the decisive factor in controlling hepatitis B in China.

Outbreak-related mumps vaccine effectiveness among a cohort of children and of young adults in Germany 2011

Mumps outbreaks in populations with high 2-dose vaccination coverage and among young adults are increasingly reported. However, data on the duration of vaccine-induced protection conferred by mumps vaccines are scarce. As part of a supra-regional outbreak in Germany 2010/11, we conducted two retrospective cohort studies in a primary school and among adult ice hockey teams to determine mumps vaccine effectiveness (VE). Via questionnaires we collected information on demography, clinical manifestations, and reviewed vaccination cards. We estimated VE as 1-RR, RR being the rate ratio of disease among two-times or one-time mumps-vaccinated compared with unvaccinated persons. The response rate was 92.6% (100/108—children cohort) and 91.7% (44/48—adult cohort). Fourteen cases were identified in the children and 6 in the adult cohort. In the children cohort (mean age: 9 y), 2-dose VE was 91.9% (95% CI 81.0–96.5%). In the adult cohort (mean age: 26 y), no cases occurred among the 13 2-times vaccinated, while 1-dose VE was 50.0% (95% CI –9.4–87.1%). Average time since last vaccination showed no significant difference for cases and non-cases, but cases were younger at age of last mumps vaccination (children cohort: 2 vs. 3 y, P = 0.04; adult cohort: 1 vs. 4 y, P = 0.03). We did not observe signs of waning immunity in the children cohort. Due to the small sample size VE in the adult cohort should be interpreted with caution. Given the estimated VE, very high 2-dose vaccination coverage is required to prevent future outbreaks. Intervention efforts to increase coverage must especially target young adults who received <2 vaccinations during childhood.

Largest Measles Epidemic in North America in a Decade—Quebec, Canada, 2011: Contribution of Susceptibility, Serendipity, and Superspreading Events

The largest measles epidemic in North America in the last decade, occurred in 2011 in Quebec, Canada, where rates of 1- and 2-dose vaccine coverage among children 3 years of age were 95%-97% and 90%, respectively, with 3%-5% unvaccinated. Case patients identified through passive surveillance and outbreak investigation were contacted to determine clinical course, vaccination status, and possible source of infection. There were 21 measles importations and 725 cases. A superspreading event triggered by 1 importation resulted in sustained transmission and 678 cases. The overall incidence was 9.1 per 100,000; the highest incidence was in adolescents 12-17 years old (75.6 per 100,000), who comprised 56% of case patients. Among adolescents, 22% had received 2 vaccine doses. Outbreak investigation showed this proportion to have been an underestimate; active case finding identified 130% more cases among 2-dose recipients. Two-dose recipients had milder illness and a significantly lower risk of hospitalization than those who were unvaccinated or single-dose recipients. A chance superspreading event revealed an overall level of immunity barely above the elimination threshold when unexpected vulnerability in 2-dose recipients was taken into account. Unvaccinated individuals remain the immunization priority, but a better understanding of susceptibility in 2-dose recipients is needed to define effective interventions if elimination is to be achieved.

Impact of a Third Dose of Measles-Mumps-Rubella Vaccine on a Mumps Outbreak

During 2009-2010, a northeastern US religious community experienced a large mumps outbreak despite high 2-dose measles-mumps-rubella (MMR) vaccine coverage. A third dose of MMR vaccine was offered to students in an affected community in an effort to control the outbreak. Eligible sixth- to 12th-grade students in 3 schools were offered a third dose of MMR vaccine. Baseline and follow-up surveys and physician case reports were used to monitor mumps attack rates (ARs). We calculated ARs for defined 3-week periods before and after the intervention. Of 2265 eligible students, 2178 (96.2%) provided documentation of having received 2 previous doses of MMR vaccine, and a high proportion (1755 or 80.6%) chose to receive an additional vaccine dose. The overall AR for all sixth- to 12th-grade students declined from 4.93% in the prevaccination period to 0.13% after vaccination (P < .001). Villagewide, overall AR declined by 75.6% after the intervention. A decline occurred in all age groups but was significantly greater (96.0%) among 11- to 17-year-olds, the age group targeted for vaccination, than among all other age groups. The proportions of adverse events reported were lower than or within the range of those in previous reports of first- and second-dose MMR vaccine studies. This is the first study to assess the impact of a third MMR vaccine dose for mumps outbreak control. The decline in incidence shortly after the intervention suggests that a third dose of MMR vaccine may help control mumps outbreaks among populations with preexisting high 2-dose vaccine coverage.

Progress in newborn hepatitis B vaccination by birth year cohorts—1998–2007, USA

In 1999, the American Academy of Pediatrics (AAP) and the U.S. Public Health Service (USPHS) issued a joint statement on thimerosal in vaccines, which advised clinicians to temporarily postpone the first dose of hepatitis B vaccine for infants born to hepatitis B surface antigen (HBsAg)-negative women. In 2005, the Advisory Committee on Immunization Practices (ACIP) updated the strategy to improve prevention of perinatal and early childhood hepatitis B virus (HBV) transmission. To evaluate the progress in hepatitis B birth dose vaccination coverage in birth year cohort from 1998 to 2007 and assess the impact of changes in ACIP recommendations on the birth dose coverage. Birth year cohort study of hepatitis B birth dose vaccination status of 200,865 children aged 19-35 months in the United States and by selected socio-demographic factors; percentage increases of hepatitis B birth dose vaccination coverage between two consecutive birth year cohorts from 1998 to 2007. From 1998 to 1999, hepatitis B birth dose vaccination coverage declined overall in the United States and among selected socio-demographic groups (P<0.001). Conversely, from 1999 to 2007 hepatitis B birth dose vaccination coverage increased significantly by birth year cohort (P<0.001), from approximately 30% in the 1999 birth year cohort to approximately 60% in the 2007 birth year cohort. The first significant increase in hepatitis B birth dose vaccination coverage occurred from 2000 to 2001 birth year cohort. Coverage increases ranged from 8.4% to 11.9% (P<0.001) in the U.S. and across all socio-demographic strata. The second largest increase in hepatitis B birth dose vaccination coverage occurred from 2005 to 2006 birth year cohort in the U.S. and among almost all socio-demographic strata, ranging from 5.6% to 8.7% (P<0.001). Forty-one of the 50 states and the District of Columbia (80%) in the U.S. had increases in hepatitis B birth dose vaccination coverage from 2005 to 2006 birth year cohort. The United States has made substantial progress in increasing hepatitis B birth dose vaccination and recovered from coverage declines associated with temporary postponement of the birth dose in 1999. The hepatitis B birth dose coverage in the U.S. remains substantially below the Healthy People 2020 target of 85%.

Susceptibility of Health Care Students to Measles, Paris, France

Susceptibility of Health Care Students to Measles, Paris, France

Progress Toward Measles Elimination in the People's Republic of China, 2000–2009

In 2006, China set a goal of measles elimination by 2012. To describe progress toward this goal, we reviewed relevant policies and strategies and analyzed national data for 2000-2009. In response to implementation of these strategies, including increased routine measles vaccination coverage and province-specific supplementary immunization activities (SIAs), reported measles incidence decreased to a historically low level of 39.5 cases per million in 2009. A synchronized nationwide SIA was scheduled in 2010 to further decrease susceptibility to measles. However, reaching and maintaining measles elimination will require strong political commitment and efforts for strengthening surveillance, increasing 2-dose vaccine coverage to >95%, stricter enforcement of the requirement to check immunization status at school entry, and careful attention to measles susceptibility in those aged ≥15 years.

Closer to the Goal: Efforts in Measles Elimination in Germany 2010

Increasing 2-dose vaccination coverage has led to an interruption of endemic measles virus circulation in Germany. However, outbreaks after virus importation still occur and contribute to international transmission chains. Between 2003 and 2009, annual measles incidence ranged between 0.2 and 2.8 per 100,000 population. Immunization gaps have been identified especially in secondary-school students and young adults, which is also reflected by a shift in age distribution of reported measles cases toward older age groups. Stronger political commitment and standardized guidelines for outbreak containment were put in place in Germany in the past years, but the last step toward measles elimination cannot be made until the number of susceptible individuals has been further reduced. In addition to routine childhood vaccination, supplementary immunization activities are needed targeting school students and young adults to close critical immunization gaps. Intensification of public awareness and sound information on vaccinations are necessary to convince skeptics and remind the forgetful.

Decline in Rotavirus Hospitalizations and Health Care Visits for Childhood Diarrhea Following Rotavirus Vaccination in El Salvador

A recent postlicensure study from El Salvador showed that the monovalent rotavirus vaccine conferred 76% protection against rotavirus hospitalizations. We further examined the impact of rotavirus vaccination on the national burden of childhood diarrhea to help assess the total public health benefits of vaccination. We compared all-cause diarrhea and rotavirus-specific hospitalization rates during prevaccine year 2006, with postvaccine years 2008 and 2009 in children < 5 years of age from 7 sentinel surveillance hospitals. We also compared annual rates of diarrhea-related healthcare events during prevaccine years 2005 and 2006 with postvaccine years 2008 and 2009 to examine the national burden of healthcare utilization for all-cause diarrhea. Among sentinel surveillance hospitals, rotavirus hospitalization rates among children < 5 years of age declined by 81% (95% confidence interval [CI]: 78%-84%) in 2008 when 2-dose rotavirus vaccine coverage was 50% among infants < 1 year; the decline was 69% (95% CI: 65%-73%) in 2009 when 2-dose vaccine coverage was 61% among infants < 1 year, compared with 2006. The greatest declines were observed in children ≤ 1 year of age, although sizeable reductions were also observed among children ≥ 2 years in 2008. National diarrhea-related healthcare visits during rotavirus season decreased by 48% (95% CI: 47%-48%) in 2008 and by 35% (95% CI: 34%-35%) in 2009 compared with the mean rate from the 2005 and 2006 rotavirus seasons. Rotavirus vaccination had a substantial public health impact on rotavirus disease and overall diarrhea events in El Salvador. Important age-related changes in diarrheal incidence emphasize the need for ongoing rotavirus surveillance after vaccine introduction.

Measles outbreaks in Micronesia, 1991 to 1994.

Several islands in Micronesia experienced large measles outbreaks, during 1991 through 1994. Except for Guam, none of the islands had reported measles outbreaks during the previous 20 years. To characterize the outbreaks, measles surveillance data, hospital records and death certificates were reviewed. Preoutbreak vaccination coverage rates were assessed by reviewing public health vaccination records. Viral isolates were genetically sequenced to determine the source of transmission. Linear regression analysis was performed to assess the effectiveness of outbreak control measures. Between 1991 and 1994 more than 1300 measles cases and 16 measles-related deaths were reported in Micronesia. Preoutbreak vaccination coverage rates among 2-year-old children were 55 to 94%. Genetic sequencing of the viral isolates and epidemiologic investigations suggested transmission between islands and new importations from outside of Micronesia. The highest attack rates were among children ages < 5 years (20/1000) and 10 to 19 years (38/1000). Compared with attack rates among children ages < 1 and 10 to 19 years, attack rates were lower among those ages 5 to 9 years, in whom 2-dose vaccination coverage rates were highest (P < 0.001). Early and rapid implementation of mass vaccination campaigns was significantly associated with shorter duration of outbreaks (P = 0.049). The measles outbreaks in Micronesia show that island populations may be highly susceptible to measles. High two-dose vaccination coverage levels must be maintained to prevent such outbreaks. Early and rapidly implemented mass measles vaccination campaigns were effective in control of island outbreaks. Strengthening public health infrastructure and surveillance is necessary for early identification of outbreaks and rapid implementation of mass campaigns.