New research suggests that babies delivered by caesarean section (C-section) are at a disadvantage when it comes to gaining immunity from a single dose of the measles vaccine. The study, published on May 13 in the journal Nature Microbiology, reveals that C-section babies are up to 2.6 times more likely to have an ineffective response to the measles jab compared to those born vaginally. This inefficacy stems from their immune systems failing to generate sufficient antibodies to combat measles infection.

However, the study also highlights a solution: a second follow-up jab induces robust immunity against measles. Co-senior study author Henrik Salje, a genetics lecturer at the University of Cambridge in the U.K., emphasises the long-term implications of birth method on disease immunity, stating, "We’ve discovered that the way we’re born—either by C-section or natural birth—has long-term consequences on our immunity to diseases as we grow up."

 Measles, being highly contagious, poses a significant threat, especially with even low vaccine failure rates potentially triggering outbreaks, as noted by researchers. Prior to the introduction of the measles vaccine in 1963, the disease claimed an estimated 2.6 million lives annually, with symptoms resembling a common cold initially, often progressing to a distinct rash and severe complications such as blindness, seizures, and death.

 Salje stresses the importance of ensuring C-section babies receive their second measles jab, as their first dose is more prone to failure. This is crucial both for individual protection and for the wider population, particularly considering that a substantial portion of children do not receive their second measles jab, raising the risk of outbreaks.

 Researchers attribute the higher failure rate among C-section babies to differences in their gut microbes. Vaginal delivery typically exposes newborns to a wider array of maternal microbes, bolstering immune system development. Salje explains, "With a C-section birth, children aren’t exposed to the mother’s microbiome in the same way as with a vaginal birth," suggesting that this delay in microbiome development may hinder the immune system's ability to respond effectively to vaccines like the measles jab.

 In the United States, approximately one in three babies (32%) is delivered via c-section, according to the March of Dimes. The study drew upon data from over 1,500 children in Hunan, China, tracking their immune response from birth to age 12 through regular blood samples. Results revealed that about 12% of children born via C-section showed no immune response to their initial measles jab, compared to 5% of vaginally born children, leaving many C-section babies vulnerable to measles following their first vaccination.

 Despite the necessity of two doses of the measles vaccine for lasting immunity, global vaccination rates remain suboptimal, with only 83% of children worldwide receiving one dose by their first birthday in 2022, marking the lowest rate since 2008, according to researchers.