Measles vaccination: influence of age on its efficacy

Effect of early measles vaccination on long-term protection: A systematic review

BACKGROUND

In North America, the first dose of a measles-containing vaccine (MCV1) is administered at ≥12 months of age. However, MCV1 may be given to infants <12 months living in highly endemic areas or traveling to these areas. Although an early dose of MCV1 leads to immediate protection, it remains unclear how this impacts long-term immunity.

METHODS

This systematic review and meta-analysis evaluates the impact of MCV1 given at <12 months vs. ≥12 months of age on long-term immunogenicity and vaccine effectiveness, with long-term defined as at least one-year post-vaccination. PubMed, EMBASE, Global Health, Web of Science and Scopus were searched on October 31st, 2019. Studies were included if they included a cohort of infants vaccinated <12 months of age and evaluated long-term immunogenicity, vaccine efficacy, or effectiveness.

RESULTS

A total of 51 texts were identified: 23 reported outcomes related to vaccine effectiveness and 30 to immunogenicity. Infants vaccinated with MCV1 < 12 months of age showed an overall higher risk of measles compared to ≥12 months of age (RR = 3.16, 95% CI: 2.00, 5.01; OR = 2.46, 95% CI: 1.40, 4.32). Risk of measles decreased with increasing age at first vaccination, with those vaccinated with one dose ≥15 months at a lesser risk compared to 12-14 months or <12 months. Measles seroconversion and seropositivity was not affected by age at first vaccination, but antibody levels were significantly lower in the MCV1 < 12-month group (MD = -0.40, 95% CI: -0.71, -0.09).

CONCLUSION

Long-term measles seroconversion and seropositivity did not appear to be affected by age at MCV1, while vaccine effectiveness decreased with younger age. There was not enough evidence to look at the effect of age at MCV1 on immune blunting.

Effect of age at vaccination on the measles vaccine effectiveness and immunogenicity: systematic review and meta-analysis

Background

The objectives of this review were to evaluate the effect of age at administration of the first dose of a measles-containing vaccine (MCV1) on protection against measles and on antibody response after one- and two-dose measles vaccinations.

Methods

We conducted a systematic review of the PubMed/MEDLINE, Embase, Web of Science and Cochrane databases (1964–2017) to identify observational studies estimating vaccine effectiveness and/or measles attack rates by age at first vaccination as well as experimental studies comparing seroconversion by age at first vaccination. Random effect models were used to pool measles risk ratios (RR), measles odds ratios (OR) and seroconversion RR of MCV1 administered at < 9, 9–11 or ≥ 15 months compared with 12 or 12–14 months of age.

Results

We included 41 and 67 studies in the measles protection and immunogenicity analyses. Older age at MCV1, from 6 to ≥15 months, improved antibody response and measles protection among one-dose recipients. Pooled measles RR ranged from 3.56 (95%CI: 1.28, 9.88) for MCV1 at < 9 months to 0.48 (95%CI: 0.36, 0.63) for MCV1 at ≥15 months, both compared to 12–14 months. Pooled seroconversion RR ranged from 0.93 (95%CI: 0.90, 0.96) for MCV1 at 9–11 months to 1.03 (95%CI: 1.00, 1.06) for MCV1 at ≥15 months, both compared to 12 months. After a second dose, serological studies reported high seropositivity regardless of age at administration of MCV1 while epidemiological data based on few studies suggested lower protection with earlier age at MCV1.

Conclusions

Earlier age at MCV1 decreases measles protection and immunogenicity after one dose and might still have an impact on vaccine failures after two doses of measles vaccine. While two-dose vaccination coverage is most critical to interrupt measles transmission, older age at first vaccination may be necessary to keep the high level of population immunity needed to maintain it.

Measles in Papua New Guinea: an age-specific serological survey

We aimed to determine the proportion of the population in Madang (Papua New Guinea) immune to measles infection by age groups, with respect to immunization status and study location, using dried blood sampling technology. We performed a prospective cross-sectional sero-survey. Population immunity against measles was sub-optimal (77%) and reported measles vaccine coverage in children <10 years of age was low (41%). The urban population was more susceptible to measles infection, compared with the rural population (66% vs 79% immune, aOR=0.6, p=0.05). Sero-conversion and long term protection rates appeared to be higher when at least one dose of vaccine was provided at or after 12 months of age (84% vs 59%, aOR=4.3, p=0.004). Such a dose is, however, not currently prescribed by the national immunization schedule.

Antimeasles antibodies in children submitted to different vaccination schedules

In order to study the measles antibody behavior of three vaccination schedules, 684 children were divided into 4 Groups: Group A (341 vaccinated children under the age of one); Group B (101 children at the age of one); Group C (74 children under the age of one and one at the age of one); Group D (163 unvaccinated children with a history of measles in the past-Group control). Children of Group A presented lower rates and 25.9% of the age group under two did not show any measles antibodies. In Group B, all the children presented antibodies. In Group C only 4.0% did not. In all age groups, the geometric mean HI antibody titers of Group A were lower than the values found in the other groups. The age at vaccination was the factor of greater influence on the results of this study.

Avaliação sorológica de imunização contra o sarampo com duas doses administradas aos 6 e 11 meses de idade: estudo prospectivo

A eficácia sorológica de um esquema de vacinação contra o sarampo empregando duas doses da vacina BIKEN CAM 70, sendo a primeira dose administrada aos 6 meses de idade e a segunda aos 11 meses de idade foi avaliada através de um estudo prospectivo. A amostra de sangue foi colhida entre 6 e 12 meses (média de 8,0 ± 1,7 meses) após a segunda dose da vacina, tendo-se empregado para pesquisa de anticorpos específicos a reação de imunofluorescência indireta (RIFI) e a técnica imunoenzimática ELISA. Anticorpos para o sarampo na amostra de sangue pós-vacinal foram detectados em 88,5% (85/96) das crianças quando foi empregada a RIFI e em 96,8% (93/96) quando se empregou a técnica imunoenzimática ELISA. Nenhuma das crianças apresentou, durante o período do estudo, quadro clínico compatível com sarampo. Em regiões em que uma proporção significativa de casos ocorrem antes dos 9 meses de idade, o esquema de vacinação de 2 doses, a primeira aos 6 e a segunda aos 11 meses de idade, pode representar alternativa válida para o controle do sarampo.