U.S. data underscore benefits of chickenpox vaccination

On November 14, the U.K. government announced that the Joint Committee on Vaccination and Immunisation (JCVI) had recommended a vaccine against chickenpox (varicella) should be added to routine childhood immunisation programme. The vaccine is to be offered to all children in two doses, at 12 and 18 months of age. A final decision to introduce the vaccine has not been taken yet.

JCVI’s recommendation comes nearly three decades after the U.S. introduced it in 1996, and a body of evidence emphasising the benefits of varicella vaccination. While chickenpox in children is most often relatively mild, some can develop complications, including bacterial infections, and in rare cases can cause encephalitis, lung inflammation, and even stroke; it can also rarely cause deaths.

Even when the disease clears, the virus stays dormant in the body and can get reactivated to cause herpes zoster (shingles), especially in adults. Exposure to the virus through children with chickenpox was expected to boost the immunity in adults and thus reduce the risk of shingles. It was theorised that vaccination of children will lead to loss of natural immunity boosting in adults, thus leading to significant increase in shingles cases. This was one of the reasons why routine administration of the vaccine in children did not begin in the U.K. earlier.

Unlike in children, chickenpox can be severe in adults. The second reason for the U.K. not introducing varicella vaccination earlier was due to the worry that unvaccinated children will become more susceptible to getting chickenpox as adults, leading to severe infection or a secondary complication. Ironically, diseases like measles and rubella are more severe in adults than in children. Yet, children are routinely vaccinated leaving unvaccinated children at great risk of severe infection as adults.

Evidence did not support the assumption of increased shingles in adults in countries that have introduced chickenpox vaccination. While a 2019 paper showed that varicella vaccination did not increase shingles incidence in adults, another study published in 2020 found that 10-20 years after adults were exposed to infected children, the protective effect against shingles was just 27%. A 2022 paper based on 25 years of data (1995-2019) from the U.S. showed a sharp drop in the incidence of chickenpox and shingles in children. In adults, shingles cases did not increase as feared. Rather, the rate of shingles in adults is expected to decline as vaccinated children become old, the study says. Unpublished results from a modelling study by the University of Cambridge found that the duration of protection from shingles was not 20 years as assumed but “likely to be around three years”, JCVI said on November 14.

Since its introduction in the U.S., the vaccine has prevented over 91 million chickenpox cases, 2,38,000 hospitalisations, and almost 2,000 deaths. The return on investment with net societal savings has been over $23 billion.

“The evidence in favour of the chickenpox vaccine has been amply clear for a while. Once again, JCVI seems to have followed an ideology of infection being beneficial for children and at population level,” Dr. Deepti Gurdasani, a clinical epidemiologist at the Queen Mary University of London told The Hindu by email. “The thinking behind not recommending the vaccine prior to now was that this may lead to an increase in shingles incidence because of lack of ‘boosting’ of the population by infected children. This has not come to pass. In fact, vaccination has been associated with a lower chance of reactivation and shingles compared to infection so far.”

As per an unpublished study by the University of Bristol, “complications from severe varicella were common, costly and placed a burden on health services. Uncomplicated varicella can also cause hospitalisation in very young children.” The JCVI statement admits that the true extent of hospitalisation due to varicella was “underestimated”. The reason: hospitalisations were “frequently due to secondary complications” arising from infection and also childhood stroke, which were “not always recorded”.

“There are several hundreds of thousands of cases of varicella each year in the U.K., most happening in under five-year-olds. While death is rare, hospitalisations do occur, with up to 4,000 admissions per year and £6.8 million in hospitalisation costs, and much greater costs associated with children being ill,” Dr. Gurdasani says. “On an economic level, chickenpox vaccination is a no-brainer. This has been clear for a really long time, as have the health benefits, which really begs the question why the JCVI has been so behind on this, and what the costs of these delays in introducing vaccination have been on both health and economy. It is unfortunate that decisions are often made on flawed thinking rather than evidence.”

India is yet to include varicella vaccine in the universal immunisation programme. “As per the NFHS-5 data for childhood vaccination, the coverage for severe diseases such as diphtheria and pertussis has only reached 76.6%. Expanding this program remains an immediate priority,” says Dr. Rajeev Jayadevan, Member, Public Health Advisory Panel, Kerala State IMA. The actual disease burden of chickenpox and shingles, and hospitalisation costs in India are not known. As a result, the cost-benefit analysis of varicella vaccination has not been done. “Published studies from Asia estimate 5 cases of shingles per 1,000 person-years, the risk increasing to 7.4-13.8 per 1,000 person-years in people over 50 years,” Dr. Jayadevan says. “Experts at the Indian Academy of Pediatrics believe the risk of shingles may be lower.”