This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.
A first vaccination dose against measles is a safe and somewhat effective option if given to infants earlier than usual, and before the age of nine months. However, vaccine effectiveness does increase when administered at older ages, as currently.
Two doses of measles-containing vaccines are recommended as part of a childhood immunisation programme. In countries with ongoing measles transmission, the first dose (MCV1) is recommended at nine months. In the UK, the MCV1 is recommended at 12 months as part of the measles, mumps and rubella (MMR) vaccination.
This review pooled data from 56 studies and found that the vaccine is around 58% effective when administered before nine months compared with 83% after nine months.
With measles on the rise in Europe and the UK, it is helpful to know that in the event of a measles outbreak, it could be used safely in younger infants as an additional measure.
Why was this study needed?
Measles is a highly contagious viral infection that can lead to life-threatening complications.
In the UK, there were 966 cases of measles in 2018, a substantial increase from the 259 cases the previous year. This has been mostly attributed to travel in Europe and large events such as music festivals.
The World Health Organization (WHO) recommends a 95% vaccination population coverage in order to achieve herd immunity. However, coverage has been reducing resulting in the return of measles outbreaks. In Europe, Asia and Africa, measles incidence has particularly increased in children younger than nine months, teenagers and adults. For people who have not been immunised, 9 out of 10 would catch measles if they came into contact with someone infected.
Due to this increase in incidence, the researchers wanted to assess whether the age for the first dose could be brought forward.
What did this study do?
This systematic review and meta-analysis identified 56 studies in which MCV1 was administered to infants under the age of nine months. The outcomes of interest included seroconversion (a sign that the immune system is reacting to the presence of the virus), antibody concentrations (levels of a protein produced by the body when it detects harmful substances), vaccine effectiveness against measles and safety.
The researchers included randomised controlled trials, quasi-randomised controlled trials, cohort and case-control studies, and outbreak investigations.
This review included studies that were observational in design. Although potential confounders can be adjusted for when interpreting the findings, it’s important to bear in mind that it isn’t possible to fully rule out the effects of other variables.
What did it find?
- Pooled results from 20 studies showed that the proportion of infants who seroconverted increased from 50% (95% confidence interval [CI] 29% to 71%) in those vaccinated with MCV1 at four months to 85% (95% CI 69% to 97%) in those vaccinated at eight months of age.
- Infants vaccinated with MCV1 between the ages of four to eight months had lower antibody levels compared with infants vaccinated after nine months (pooled mean antibody titre ratio 0.46, 95% CI 0.33 to 0.66). However, there was very wide variability between the studies which reduces the confidence in this result.
- The pooled vaccine effectiveness of MCV1 in infants younger than nine months was 58% (95% CI 9% to 80%) according to eight studies. A similar proportion was effectively vaccinated when using within-study comparisons from five studies, at 51% (95% CI -44% to 83%) compared with the increased effectiveness above nine months of 83% (95% CI 76% to 88%).
- There were no differences in the risk of adverse events between infants administered with MCV1 under or over the age of nine months.
What does current guidance say on this issue?
The UK immunisation schedule: the green book (updated in 2020) recommends administering the first dose of the MMR vaccine in infants on their first birthday or soon after. MMR2 is recommended at age three and four months, or soon after.
The WHO recommendations for routine immunisation in countries with low levels of transmission are that MCV1 be administered at 12 months of age. MCV2 is suggested to be administered based on programmatic considerations to achieve the highest coverage. The WHO also has a range of recommendations for when to give measles vaccines earlier in countries with higher rates of measles, including an extra dose (MCV0) before nine months during an outbreak.
What are the implications?
This review’s findings indicate that vaccine administration before nine months can still provide useful protection against measles and could, therefore, be an effective solution in areas where there is a high risk of contracting the disease.
In the UK, administering the first dose of MCV under nine months is considered to be an extra dose, and is currently considered if an infant is in contact with a child with measles or as an emergency solution to contain any measles outbreaks. If this occurred, the usual doses would be subsequently given from 12 months to ensure full immunity.
Citation and Funding
Nic Lochlainn LM, de Gier B, van der Maas N et al. Immunogenicity, effectiveness, and safety of measles vaccination in infants younger than 9 months: a systematic review and meta-analysis. Lancet Infect Dis. 2019;19(11):1235-45.
Funding was provided by the World Health Organization (WHO).
Bibliography
NHS website. Measles. London: Department of Health and Social Care; 2018.
Oxford Vaccine Group. Vaccine Knowledge Project: authoritative information for all. Oxford: University of Oxford; updated 2019.
PHE. UK immunisation schedule: the green book, chapter 11. London: Public Health England; 2019.
WHO. Recommendations for routine immunization. Geneva: World Health Organization; 2019.
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