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Shanghai The first measles vaccination may provide lower protection in infants born by cesarean section. This is suggested by the results of an observational study from China Nature Microbiology (2024; DOI: 10.1038/s41564-024-01694-x). After the second dose of vaccination, however, there were no longer any differences to the children born naturally.

The development of intestinal flora is often delayed in babies born by cesarean section. They lack the starting dose of microorganisms that newborns normally receive as they pass through the birth canal. The colonization of the intestine with microorganisms provides important impulses for the development of the immune system.

The intestine is a school of the immune system because the defense cells there are constantly confronted with new antigens. A team led by Hongjie Yu from Fudan University in Shanghai and Henrik Salje from the University of Cambridge discovered by chance that this could have an impact on the effectiveness of vaccinations.

The researchers wanted to clarify why measles epidemics continue to occur in China despite a high vaccination rate and why a third of children fall ill despite vaccination. The researchers initially suspected that this was related to the early first vaccination date. Children in China receive the first dose of the measles vaccination at the age of eight months. During this time, the vaccination protection that the children receive through the antibodies from the mother’s blood is lost.

Dutch researchers had… Lancet Infectious Diseases (2019; DOI: 10.1016/S1473-3099(19)30396-2) put forward the hypothesis that the maternal antibodies weaken the reaction of the child’s immune system (blunting) and the infants are therefore not adequately protected against measles, especially if the second dose is given relatively late (in China at the age of 18 months). In fact, Yu and Salje were able to show that vaccination leads to a greater increase in antibody titers after 12 and 24 months.

However, they made another observation: In 12% of the children born via cesarean section, there was only an insufficient increase in antibody titers after the first vaccination, which would probably not be sufficient for vaccination protection. The proportion of children who were born naturally was only 5%. The odds ratio of 2.56 was statistically significant with a 95% confidence interval of 1.06 to 6.37.

Since more than one in three children (38%) in China are born by cesarean section, this could explain at least some of the illnesses that occurred among vaccinated children. However, the results also show that the vaccination gap was closed by the second vaccination dose. Here, children born by caesarean section received equally good protection.

Other researchers had recently come to similar results. A team led by Debby Bogaert from the University of Edinburgh reported in Nature Communications (2022; DOI: 10.1038/s41467-022-34155-2) found that vaccination against pneumococci at 12 months of age and against meningococci at 18 months of age achieved lower antibody titers in children born by cesarean section.

A team led by Jie Li from Beijing University observed that vaginal birth and breastfeeding had a positive effect on the immune response to a hepatitis B vaccination (Journal of Clinical and Translational Hepatology 2023; DOI: 10.14218/JCTH.2022.00032S). © rme/aerzteblatt.de