The current global resurgence in measles is having its resonance in Kerala too, which has been witnessing a serious surge in the disease since January.
Across the globe, huge local outbreaks have been caused by travel as well as the increase in unvaccinated populations.
In Kerala, however, majority of the cases are reported from Thiruvananthapuram, which has good vaccination coverage and amongst people who are well-nourished and have received at least one dose of vaccine in their lifetime.
Kerala reports around 600 plus cases of measles every year. This year, as many cases have been reported in the first four months itself, with over 50% cases in the 19-40 year age group. There are also cases in the less than nine months age group, but fewer cases than before in the 1-5 years group.
“When universal routine immunisation in childhood improves and the virus is still in circulation, the disease will naturally move to the older age group who may be unimmunised or whose vaccine-derived immunity has begun to wane. At a time when the State is moving towards measles elimination, adult measles is a major concern,” a senior health official said.
Historically, measles has been a childhood disease. The epidemiological shift to older population presents new public health challenges because of the increased severity of the disease, especially in vulnerable populations like pregnant women and immunocompromised patients (HIV, organ transplant recipients on immunosuppressants, cancer patients), who cannot be vaccinated with the live attenuated measles vaccine.
“Earlier, nearly 90% of measles cases could be managed on out-patient basis. This year, most cases are in the 19-35 age group and over 60% of the cases had to be admitted as in-patients, with a good percentage requiring ICU management,” said R. Aravind, head of infectious diseases at Thiruvananthapuram Medical College.
The changing epidemiology of measles has not just brought forth the several unknowns but also raised important questions on whether adult immunisation should be a policy, on vaccine potency and the adequacy of vaccine immune response.
Though measles vaccine is highly immunogenic, as part of the national measles elimination strategy, a mandatory second dose at 15-18 months was introduced in 2010, so that there is better immune protection. It is fairly certain that those currently in the 18-40 years age group have not had the protection of the second dose and may be one reason for the increase in cases in this age group.
The first vaccination age for measles has been fixed at nine months because till then, the maternal antibodies transferred in utero are supposed to afford protection to the child. If vaccinated earlier, the maternal antibodies might interfere with the immune response to vaccine.
However, at Rajiv Gandhi Centre for Biotechnology, the director, M. Radhakrishna Pillai and team, who are currently studying the efficacy of measles vaccination in South India, has reported that children under the recommended vaccination age of nine months are highly susceptible to measles.
SAT Hospital too has recently reported the death of an infant younger than nine months due to measles.
“If the young mothers of the day does not have sufficient antibody protection, how do we protect infants younger than nine months against measles? Given measles’ age shift to older age group, should we move the vaccination age to 12 months for better vaccine response?
“Is a third dose of MMR (mumps-measles-rubella) necessary?And should we recommend that all adults be given a dose of MMR as the virus is still in circulation? These questions need to be looked at from a research perspective by the State/National Technical Advisory Group on Immunisation,” a public health expert said.