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California’s Berkeley School of Public Health in the US has found that undernutrition may play an important role in measles outbreaks in low- and middle-income countries, even among children who have been fully vaccinated.

In November 2024, the World Health Organisation and the US Centres for Disease Control and Prevention reported that worldwide about 10.3 million cases of measles had occurred in the previous year. According to of UP’s , and the South African principal investigator on the study, most vaccine assessments are conducted in well-nourished populations with a higher socio-economic status, yet the vaccines are often used in populations where there are high incidences of malnutrition. While under-vaccination is undoubtedly a driver of these outbreaks, the possible role of undernutrition in low- and middle-income countries has not been clear.

This study, which was published in medical journal Vaccine, has offered more clarity.

“Our findings emphasise that addressing child undernutrition may improve vaccine efficacy and reduce the burden of vaccine-preventable diseases,” Prof Bornman explained. “The findings of this study could also apply to other countries with similar food insecurity and nutrition shortcomings.”

“The results show that child undernutrition could have a negative impact on the efficacy of vaccines by compromising the immune system’s ability to mount an effective response to certain types of vaccines,” explained lead author of the paper Prof , director of the at the Berkeley School of Public Health. 

The study followed 621 fully vaccinated children up to age five, all of whom were part of the Venda Health Examination of Mothers, Babies and the Environment (VHEMBE) birth cohort in South Africa, an existing research programme. The researchers examined the relationship between undernutrition – as measured by stunting and other growth measures – and the vaccine-specific serum antibody level of three different vaccine types: measles, tetanus and Haemophilus influenzae type (Hib). Children who were stunted or had any indicator of diminished growth at three and a half years old showed a 24.1% or 27.2% lower level of antibodies for measles, respectively, compared to the children with normal growth.

“For certain vaccines, such as the tetanus vaccine, our data suggests that some of the negative impacts of undernutrition may be sex-specific, with girls being less likely to be protected than boys,” Prof Eskenazi said.

“In 2022, about 22.3% or 148 million children under five years of age worldwide were stunted, with the highest burden in Asia and sub-Saharan Africa,” added , Associate Professor of Epidemiology at McGill University and US principal investigator of the study. “Undernutrition is associated with deficiencies in energy and essential nutrients that may impair the development of an adequate immune response to vaccines.”

Furthermore, even if a sufficient response had initially developed, an undernourished child may not maintain long-term protection.

“It is imperative that we vaccinate children against infectious diseases to prevent unnecessary disease and deaths,” Prof Eskenazi said. “Given our data, which suggests that children who are undernourished may not be protected adequately even when fully vaccinated, we must also address worldwide undernutrition in children. This is especially important with climate change and the future possibility of new infectious diseases.”