Kerala's Measles Outbreaks Prompt Call to Rethink Disease Epidemiology and Immunity Gaps

As of November 6, Kerala's Integrated Disease Surveillance Programme had logged 824 confirmed and 1,681 probable measles cases across the state. Five deaths have been reported as measles-related, but only one has been confirmed so far. The outbreaks have been concentrated in Kozhikode, Malappuram and Palakkad, and they are pushing public health experts to ask whether the disease in Kerala (Keralam) still behaves the way the vaccination schedule assumes.

For decades measles was treated as a childhood illness, mostly striking children between one and five. That is no longer the pattern. Cases are now turning up across age groups, among fully vaccinated people, and among infants younger than nine months, who are too young for the routine vaccine. The last major surge came in 2022-23.

Measles vaccine entered the Universal Immunisation Programme in 1985 as a single dose at nine months. The timing was chosen so that maternal antibodies, passed across the placenta, would not blunt the baby's response to the vaccine. A second dose at 18 months was added in 2010 to close gaps left by the first and to support elimination. The changing age profile of cases raises the question of whether that design still holds.

K.K. Purushothaman, former Professor of Paediatrics at Government Medical College, Thrissur, points to infants falling ill before nine months, possibly because mothers of the present generation carry lower levels of measles antibodies. He also sees a sizeable share of cases among older adults. He argues the state should consider another measles-containing dose under the UIP, either in adolescence or for women before marriage. In his view the State Technical Advisory Group on Immunisation should examine the idea and commission serological studies of adolescents and young women to measure their protective antibody levels.

There is outside evidence for the concern. After the 2023 outbreaks in Mumbai, when more than 31% of reported cases were infants under nine months, a seroprevalence study found only 66.8% of mothers had enough antibodies to protect their babies. A WHO informal technical consultation report, published in Vaccine in May 2025, acknowledged that women who gained immunity through vaccination rather than natural infection might pass on lower antibody levels. But the experts judged the evidence insufficient to change the recommendation of a first dose at 9-15 months.

Research closer to home complicates the picture further. A study by the Rajiv Gandhi Centre for Biotechnology, published in JAMA Network Open in August 2025, tested 684 children aged four to 18 from Keralam and Tamil Nadu, all with at least two doses of a measles-containing vaccine, along with 544 mothers. Of the children, 8.5% lacked protective antibody levels. Another 89 (13%) tested positive for measles-specific IgM, which can indicate recent infection, and 90 (13.2%) had borderline results. The researchers read this as suggesting recent exposure and possible breakthrough infections. Some 435 children (63.6%) had received a third dose and seven a fourth, yet responses still varied. Antibody levels alone, the source notes, do not establish whether a person will develop clinical measles.

Incomplete immunisation is still a major driver. First-dose coverage of the measles-rubella vaccine is generally around 95%, but second-dose coverage has stayed lower, at 85-88%, and worse in some districts. The Health department has often tied outbreaks to Malappuram and Kozhikode, where gaps are substantial, yet experts note pockets of under-immunisation exist statewide and cases are appearing in every district, among unvaccinated, partially vaccinated and fully vaccinated children.

WHO's elimination strategy rests on high two-dose coverage, effective surveillance and rapid outbreak response. What Kerala lacks, the analysis argues, is the breakdown: how many laboratory-confirmed cases had two verified doses, how many had partial or no immunisation, and how ages are distributed. That evidence would show whether coverage gaps alone explain the outbreaks or whether waning or inadequate immunity is also at work.