Published Aug 07, 2026 | 1:53 PM ⚊ Updated Aug 07, 2026 | 1:53 PM
Vaccination with the MMR vaccine is the most effective way to prevent mumps infections. (Shutterstock)
Synopsis: Kerala’s prolonged mumps outbreak has taken a new turn, with researchers detecting a previously unreported virus genotype in the state, adding to concerns over the disease’s rapid spread. The finding has also put a renewed focus on vaccine policy, outbreak surveillance and the growing demand to include the MMR vaccine in the universal immunisation programme.
For more than two years, Kerala’s health officials and researchers have been trying to understand an unusual surge of a contagious disease: mumps.
What was once considered a common childhood illness has returned on a much larger scale, spreading well beyond children and increasingly affecting adolescents and young adults.
Cases shot up from just 2,324 in 2023 to over 70,000 in 2024, and the virus has continued to circulate this year, with 5,779 infections reported in 2026, including 341 in July and 43 cases this month (up to 5 August).
Now, a fresh finding has added another piece to the puzzle.
Researchers have found that Kerala is not dealing with just one strain of the virus, as previously believed.
Another strain is also circulating in the state.
The discovery has drawn attention because the mumps vaccine widely used in India is based on a particular strain, raising questions about whether this mismatch is helping the virus continue to spread, particularly in crowded settings such as schools and colleges.
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The first genomic evidence of mumps virus genotype C circulating in Kerala has been reported by researchers, a finding that could strengthen efforts to track the virus and assess the effectiveness of existing vaccination strategies.
The study, carried out by researchers at the ICMR–National Institute of Virology (NIV), Kerala Unit, Alappuzha, found that some mumps virus samples subjected to whole-genome sequencing belonged to genotype C. The findings have been published in Elsevier’s Infection, Genetics and Evolution journal in July.
Mumps is a highly contagious viral disease that primarily affects the salivary glands.
While it is usually mild and self-limiting, it can occasionally lead to serious complications, including encephalitis, hearing loss and orchitis, a painful inflammation of the testicles seen in around one in five infected young adult males.
The study comes against the backdrop of a sharp rise in reported mumps cases in Kerala since 2024.
Between March 2024 and March 2025, the State-Level Viral Diagnostic and Research Laboratory (SL-VRDL) at the ICMR–NIV Kerala Unit tested 197 suspected cases, of which 58 were confirmed through qRT-PCR (quantitative reverse transcription polymerase chain reaction, a method to detect and quantify RNA in a sample).
Most infections were reported among children aged 5-9 years and adolescents between 10 and 19 years.
Then, a subset of the confirmed samples was selected for whole-genome sequencing to understand the molecular epidemiology of the virus.
According to lead author B Anukumar of the ICMR–NIV Kerala Unit, increased reporting of mumps cases across the state prompted enhanced laboratory surveillance, enabling researchers to characterise the genetic diversity of the circulating strains.
The genomic analysis showed that the selected strains differed from the L-Zagreb vaccine strain, which belongs to genotype N and is commonly used in India.
The selected samples were identified as genotype C.
Researchers, however, cautioned that the biological significance of these genetic differences remains unclear and requires further investigation.
The mumps virus has only one serotype, but variations in its small hydrophobic (SH) gene allow it to be classified into 12 distinct genotypes, assigned letters from A to N (excluding E and M).
The researchers said the findings underscore the importance of continued molecular surveillance to monitor viral evolution and understand whether genetic changes could have implications for vaccine performance. They also said the evidence adds to the case for evaluating the inclusion of a mumps-containing vaccine in the Universal Immunisation Programme (UIP).
The study was supported under the Virus Research and Diagnostic Laboratory (VRDL) scheme of the Department of Health Research, Ministry of Health and Family Welfare.
Another important aspect of the study is its recommendation to include the measles-mumps-rubella (MMR) vaccine in UIP, saying it could play a key role in reducing the growing disease burden.
The study argues that India continues to have a significant mumps burden and says the exclusion of mumps vaccination from the national immunisation schedule remains a gap in disease prevention. It recommends introducing a mumps-containing vaccine, preferably the MMR vaccine, under the UIP.
Meanwhile, the researchers said the recent rise in mumps cases in Kerala cannot be attributed solely to genetic changes in the virus or vaccine failure.
Although the circulating virus strains differ genetically from the vaccine strain, the study cautioned against treating this as evidence of reduced vaccine protection in the absence of vaccination records, immunological data and vaccine effectiveness studies.
The findings point instead to a combination of factors, including gaps in immunisation coverage and a growing pool of susceptible individuals.
In Kerala, mumps vaccination was available until 2017 before it was discontinued, a move the researchers say may have contributed to increased susceptibility among children and adolescents.
However, the absence of vaccination history for most patients in the study prevented an assessment of breakthrough infections.
Kerala had briefly incorporated the MMR vaccine into its immunisation programme in 2014 by replacing the second dose of the measles vaccine administered at 18 months. The move was aimed at strengthening protection against rubella. However, the state reverted to the Centre’s schedule in 2017 after the nationwide rollout of the Measles-Rubella (MR) vaccine under the UIP. The MR vaccine, given at nine and 15 months, protects against measles and rubella but does not cover mumps.
Referring to earlier seroprevalence data from Vellore, the researchers said continued exposure to the virus across age groups points to ongoing community transmission and gaps in herd immunity.
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At the same time, the resurgence of mumps in Kerala has once again brought into focus the long-pending demand to include the MMR vaccine in the UIP, with paediatricians and public health experts arguing that the disease has long been underestimated in India.
Although mumps is a vaccine-preventable disease, it has never been included in the national immunisation schedule.
The disease was traditionally viewed as having low public health importance because it rarely causes deaths.
However, the Indian Academy of Paediatrics (IAP) has consistently maintained that this assessment overlooks the true burden of the disease, pointing to poor documentation of cases, inadequate follow-up of patients, limited reporting of complications and the absence of comprehensive studies.
India also lacks nationally representative data on the incidence of mumps, while its long-term health effects, particularly those affecting the reproductive system, remain insufficiently studied.
With repeated outbreaks now being reported, Kerala has written to the Centre seeking the replacement of the MR vaccine with the MMR vaccine under the national programme.
The demand has found support beyond Kerala.
Earlier in 2024, officials of the Tamil Nadu Directorate of Public Health and Preventive Medicine strongly argued for the inclusion of the MMR vaccine in the UIP.
They noted that while children under the national programme receive protection against measles and rubella, the mumps component remains available only through vaccines in the private sector, placing it beyond the reach of a large section of the country’s children.
Public health experts point out that the absence of routine immunisation against mumps has left successive generations of children vulnerable to periodic outbreaks. Before vaccination became available, mumps typically resurfaced in epidemic cycles every four to five years. Factors such as overcrowding, poor sanitation and uneven access to healthcare continue to facilitate transmission in many parts of the country.
Experts also warn that the disease is not always benign.
Besides causing outbreaks in schools and communities, mumps can lead to complications such as orchitis, which has been associated with subfertility, reduced sperm count and, in some cases, infertility.
They argue that wider use of the MMR vaccine would not only reduce infections and complications but also lessen the financial burden on families during recurring outbreaks.
The researchers also stressed the need for sustained molecular surveillance and vaccine effectiveness studies to determine whether the genetic variations identified in circulating strains have any impact on protection offered by existing vaccines.
