Vaccination Levels Associated with Lack of Measles Transmission among Preschool-Aged Populations in the United States, 1989–1991

Combining serological and contact data to derive target immunity levels for achieving and maintaining measles elimination

BACKGROUND

Vaccination has reduced the global incidence of measles to the lowest rates in history. However, local interruption of measles virus transmission requires sustained high levels of population immunity that can be challenging to achieve and maintain. The herd immunity threshold for measles is typically stipulated at 90-95%. This figure does not easily translate into age-specific immunity levels required to interrupt transmission. Previous estimates of such levels were based on speculative contact patterns based on historical data from high-income countries. The aim of this study was to determine age-specific immunity levels that would ensure elimination of measles when taking into account empirically observed contact patterns.

METHODS

We combined estimated immunity levels from serological data in 17 countries with studies of age-specific mixing patterns to derive contact-adjusted immunity levels. We then compared these to case data from the 10 years following the seroprevalence studies to establish a contact-adjusted immunity threshold for elimination. We lastly combined a range of hypothetical immunity profiles with contact data from a wide range of socioeconomic and demographic settings to determine whether they would be sufficient for elimination.

RESULTS

We found that contact-adjusted immunity levels were able to predict whether countries would experience outbreaks in the decade following the serological studies in about 70% of countries. The corresponding threshold level of contact-adjusted immunity was found to be 93%, corresponding to an average basic reproduction number of approximately 14. Testing different scenarios of immunity with this threshold level using contact studies from around the world, we found that 95% immunity would have to be achieved by the age of five and maintained across older age groups to guarantee elimination. This reflects a greater level of immunity required in 5-9-year-olds than established previously.

CONCLUSIONS

The immunity levels we found necessary for measles elimination are higher than previous guidance. The importance of achieving high immunity levels in 5-9-year-olds presents both a challenge and an opportunity. While such high levels can be difficult to achieve, school entry provides an opportunity to ensure sufficient vaccination coverage. Combined with observations of contact patterns, further national and sub-national serological studies could serve to highlight key gaps in immunity that need to be filled in order to achieve national and regional measles elimination.

Bias with respect to socioeconomic status: A closer look at zip code matching in a pneumococcal vaccine effectiveness study

In 2010, 13-valent pneumococcal conjugate vaccine (PCV13) was introduced in the US for prevention of invasive pneumococcal disease in children. Individual-level socioeconomic status (SES) is a potential confounder of the estimated effectiveness of PCV13 and is often controlled for in observational studies using zip code as a proxy. We assessed the utility of zip code matching for control of SES in a post-licensure evaluation of the effectiveness of PCV13 (calculated as [1-matched odds ratio]*100). We used a directed acyclic graph to identify subsets of confounders and collected SES variables from birth certificates, geocoding, a parent interview, and follow-up with medical providers. Cases tended to be more affluent than eligible controls (for example, 48.3% of cases had private insurance vs. 44.6% of eligible controls), but less affluent than enrolled controls (52.9% of whom had private insurance). Control of confounding subsets, however, did not result in a meaningful change in estimated vaccine effectiveness (original estimate: 85.1%, 95% CI 74.8–91.9%; adjusted estimate: 82.5%, 95% CI 65.6–91.1%). In the context of a post-licensure vaccine effectiveness study, zip code appears to be an adequate, though not perfect, proxy for individual SES.

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Socioeconomic status (SES) may impact enrollment in vaccine effectiveness studies.

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We assessed zip code matching as a proxy for SES in a pneumococcal vaccine study.

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After zip code matching, we found differences in SES between cases and controls.

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Differences did not appear to substantially bias estimated vaccine effectiveness.

Does an education seminar intervention improve the parents' knowledge on vaccination? Evidence from Yiwu, East China

BACKGROUND

caregivers' knowledge on vaccination is an important impact factor for their children's vaccination status. The aims of this study were to evaluate the caregivers' knowledge of vaccination, and to assess effectiveness of a health education seminar for improving caregivers' knowledge on immunization.

METHODS

pre- and post-assessment design was adopted for a single group to evaluate the effectiveness of the health education seminar on vaccination. The seminar consisted of a lecture using simple understandable language. Improvements in total knowledge score before and after the seminar were assessed using a validated questionnaire that included ten questions. Description analysis and non-parametric tests were applied to evaluate and compare the vaccination knowledge level before and after the seminar.

RESULTS

378 caregivers participated in this study. The majority were mothers. Of the ten questions, the correct response rates had significantly increased for nine questions after the education seminar. The mean total score of the assessment before the seminar was 5.2 ± 1.2 while that was 8.4 ± 0.9 for the assessment after the seminar, with a significant increase of 3.18 points.

CONCLUSION

a short education seminar designed for caregivers had a remarkable effect on their vaccination knowledge. Health education on vaccination targeting migrant caregivers, caregivers with lower education level or household income, and employed caregivers are needed in future.

Geographic clustering of nonmedical exemptions to school immunization requirements and associations with geographic clustering of pertussis

School immunization requirements are important in controlling vaccine-preventable diseases in the United States. Forty-eight states offer nonmedical exemptions to school immunization requirements. Children with exemptions are at increased risk of contracting and transmitting vaccine-preventable diseases. The clustering of nonmedical exemptions can affect community risk of vaccine-preventable diseases. The authors evaluated spatial clustering of nonmedical exemptions in Michigan and geographic overlap between exemptions clusters and clusters of reported pertussis cases. Kulldorf's scan statistic identified 23 statistically significant census tract clusters for exemption rates and 6 significant census tract clusters for reported pertussis cases between 1993 and 2004. The time frames for significant space-time pertussis clusters were August 1993-September 1993, August 1994-February 1995, May 1998-June 1998, April 2002, May 2003-July 2003, and June 2004-November 2004. Census tracts in exemptions clusters were more likely to be in pertussis clusters (odds ratio = 3.0, 95% confidence interval: 2.5, 3.6). The overlap of exemptions clusters and pertussis clusters remained significant after adjustment for population density, proportion of racial/ethnic minorities, proportion of children aged 5 years or younger, percentage of persons below the poverty level, and average family size (odds ratio = 2.7, 95% confidence interval: 2.2, 3.3). Geographic pockets of vaccine exemptors pose a risk to the whole community. In addition to monitoring state-level exemption rates, health authorities should be mindful of within-state heterogeneity.

[Epidemiological investigation of a measles outbreak in a preschool in Incheon, Korea, 2006]

OBJECTIVES

This study describes a plan that was designed to prevent a measles outbreak that showed a changed outbreak pattern. This study is based on the epidemiological investigation of a measles outbreak in a preschool in Incheon, Korea, 2006.

METHODS

The subjects were 152 students at a preschool where a measles outbreak occurred. A questionnaire survey was conducted and serological testing for measles specific IgM was preformed.

RESULTS

Of the fifteen confirmed, identified cases, eleven patients had been vaccinated with one dose, one patient had received two doses and three patients were unvaccinated. The three unvaccinated cases consisted of one 5-year-old child, one 3-year-old child and one 16-month-old infant. For the cases with one dose of the vaccination, there were 11 cases, which consisted of six 5-year-old children, two 4-year-old children, two 3-year-old children and one 2-year-old child. The case with two doses of the vaccination was one 4-year-old child. The attack rate of measles was 100% in the 0-dose group, 11.2% in the 1-dose group and 2.0% in the 2-dose group. The vaccine's efficacy was 88.8% in the 1-dose group and 98.0% in the 2-dose group. The vaccine effectiveness for the 2-dose group was higher than that of the 1-dose group.

CONCLUSIONS

High coverage with a 2-dose vaccination should be maintained, and the vaccination should be given at the suitable time to prevent a measles outbreak with a changed outbreak pattern.

Measles outbreaks affecting children in Jewish ultra-orthodox communities in Jerusalem

In 2003 and 2004 two measles outbreaks occurred in Jewish ultra-orthodox communities in Jerusalem. The index case of the first outbreak (March 2003) was a 2-year-old unvaccinated child from Switzerland. Within 5 months, 107 cases (mean age 8.3+/-7.5 years) emerged in three crowded neighbourhoods. The first cases of the second outbreak (June 2004) were in three girls aged 4-5 years in one kindergarten in another community. By November 2004, 117 cases (mean age 7.3+/-6.5 years) occurred. The virus genotypes were D8 and D4 respectively. Altogether, 96 households accounted for the two outbreaks, with two or more patients per family in 79% of cases. Most cases (91.5%) were unvaccinated. Immunization coverage was lower in outbreak than in non-outbreak neighbourhoods (88.3% vs. 90.3%, P=0.001). Controlling the outbreaks necessitated a culture-sensitive approach, and targeted efforts increased MMR vaccine coverage (first dose) to 95.2%. Despite high national immunization coverage (94-95%), special attention to specific sub-populations is essential.

Immune response to measles vaccine in primary school students

This cross sectional study was performed to estimate the prevalence of serological evidence of immunity to Measles in primary school students (age 6-12) that have a history of twice vaccination against measles, on 9 and 15 month old and determining the appropriate age to re-vaccination. Multistage sampling was used to select students to participate in the present study. Immunization status and documentary evidence of immunization was recorded from the Personal Health Record. Measles antibodies were measured using enzyme-linked immunosorbent assay (ELISA). Sufficient blood for antibody testing was obtained from 1665 children, 975 (57%) were girls and 720 (43%) were boys, respectively and mean age was 9.17 +/- 1.53 years. On the whole, 1198 subjects (72%) were seropositive and 467 (28%) were seronegative at all. Among girls and boys, 72 and 71%, were seropositive respectively. These differences were not statistically significant between the two sexes (p = 0.404). Antimeasles antibody titer decreased with increasing age from 6 to 10 years old, (76.5% in 6 years old group vs. 71% in 10 years old group) and then rise to 78% in 11-12 years old group. These differences were not statistically significant between age groups (p = 0.775). the immunity produced by the measles vaccine is not enough. Decrease of protective effect of measles vaccine, suggests the necessary of preschool revaccination.

Understanding variation in measles-mumps-rubella immunization coverage--a population-based study

BACKGROUND

Coverage of the Measles-Mumps-Rubella combined vaccine (MMR) has declined in recent years in the UK, following adverse publicity about possible links between the vaccine, autism, and Crohn's disease. The objectives of this study were to assess geographical variation in trends in MMR coverage and to identify the factors affecting MMR uptake at population level.

METHODS

We conducted an ecological study of immunization coverage by second birthday, based on routinely collected data from 1993-2004 for England. Trends in MMR uptake were assessed in 95 District Health Authorities in England over the study period. We investigated the relationship between MMR immunization uptake and deprivation, ethnicity, education, population density, rurality, and socioeconomic class.

RESULTS

Since 2000, MMR coverage has declined significantly in virtually all areas of England. Population density and deprivation were both strongly correlated with low MMR uptake. The decline in coverage since 1993-94 was significantly related to the proportion of educated population and was greater in densely populated areas.

CONCLUSION

Decline in MMR coverage now affects most areas of England. The lowest rates of MMR coverage remain in urban areas, particularly in inner cities, which also tend to show high levels of deprivation. Public health resources should continue to target inner city areas, as well as focus on the concerns of the better educated about vaccine safety.

Measles

PURPOSE OF REVIEW

The purpose of this review is to summarize important papers concerning measles disease and measles-containing vaccines published in 2004.

RECENT FINDINGS

Endemic measles has been successfully controlled in the Americas and, to a lesser extent, in Europe. This has been achieved with a high uptake of two doses of a measles-containing vaccine. Even in industrialized countries, where vaccine uptake is poor, for example Japan, the disease is still a significant cause of morbidity and mortality. Vaccine failure is predominantly due to primary vaccine failure, which may, in part, be genetic in origin and related to HLA type. Measles-containing vaccines have been shown to be associated with febrile convulsions, but there is no strong evidence of a link with atopy. There is considerable evidence that there is no causal relationship with autistic disorders. In spite of this, many parents and some professionals have concerns about the safety of the vaccines, which may lead to their underuse.

SUMMARY

It is possible to eliminate measles with a high uptake of two doses of measles-containing vaccine, but concerns about safety persist and need to be tackled. More research is required into how to do this effectively and also to elucidate the causes of vaccine failure.