‘Protective’ vaccine doses will strengthen defences against Covid

To extend the protective cordon further, children in the 15-18 year age group will be eligible to get vaccinated from January 3, 2022 through a full vaccination schedule. Though it has been generally observed all over the world that infected children mostly experience mild illness, a high incidence of infection in the highly mobile age group may make some of them quite sick or predisposed to long-term complications. The move to provide vaccine protection to older children will comfort their parents and teachers. Coincidentally, regulators have now approved the use of Bharat Biotech’s Covaxin in the 12-18 age group. It joins Zydus Cadila’s DNA vaccine (Zycov-D) as an approved paediatric vaccine.

The much-awaited announcement on permitting third doses comes as a relief to many elderly persons and frontline health workers who have been anxiously weighing the risks posed by a rapidly spreading new variant — Omicron. They are concerned that the immunity they acquired in the first half of 2021 is unlikely to be protective this time against Omicron or even Delta which is still around. Accumulating global data and available sparse Indian data on breakthrough infections and re-infections align with the conclusion that Omicron has a high propensity for immune escape. Comfortingly, global data also reveal that third dose “boosters” will largely restrict Omicron and Delta infections to mild clinical illness which does not require hospitalisation or result in death.

Though the decision to expand vaccination coverage has been widely welcomed, some issues require clarification. Those guidelines may be provided by the government in the coming days. The questions pertain to the mode of ascertainment of eligibility for the elderly, the choice of vaccine for the third dose and the procedure for registration and certification.

The eligibility of frontline healthcare workers can be easily ascertained, as was done in the first half of 2021. Eligibility criteria for the elderly now come with a qualifier that a doctor must advise a third dose on the grounds of a “comorbidity” being diagnosed. Earlier, age alone was the criterion for registering an elderly person, aged 60 years or above, for Covid vaccination. Nether a documentary proof of comorbidity nor a physician’s referral was needed. Will anyone above 60 years be able to register even now, without a formal document attesting co-morbidity? I hope so. If such proof is required, it may place poor people without ready access to a doctor at a disadvantage, especially in rural areas. In any case, there is a high prevalence of comorbidities in the 60+ age group. That justifies the presumption of the presence of a co-morbidity in any person aged 60 years or older. The COWIN app will probably be upgraded to provide the pathway for freshly eligible older adults and children.

There is another group that needs to be considered as a priority group for administering the protective dose. These are persons of any age who are immunocompromised. They have low immunity due to a disease that makes them immunodeficient or are receiving therapies that suppress their immunity. Two doses of the vaccines are likely to elicit a weak or short-lasting immune response in such persons. Additional vaccine doses may raise their immunity levels and protect against severe Covid. Perhaps revised guidelines from the government will explicitly describe the eligibility criteria for these groups.

Presently, only two vaccines are widely available in our vaccination programme. Will there be more soon? This question is pertinent because global experience suggests that a “heterologous” booster (a vaccine different from the previous two doses) is better than a ‘homologous’ repeat of the same vaccine. There is conflicting evidence from studies about how effective a third dose of the AstraZeneca vaccine is against Omicron. We do not yet have national data on boosters. However, an accidental crossover in a small number of persons in Uttar Pradesh produced some evidence that a relay vaccination of Covishield and Covaxin resulted in a high immune response.

Decisions related to heterologous and homologous vaccines will await government guidelines. Even if left to a physician’s judgement, the supply chain situation will guide the selection of the third dose. If more varieties of vaccines are available, the choice of a heterologous third dose will be easier. In that context, the arrival of the subunit protein vaccines will be eagerly awaited, even as nasally administered mucosal vaccines are being trialled.

Restricting eligibility for the third dose to high risk groups of adults and older children at this stage is a wise decision for two reasons. The supply chain of vaccines is still not wide enough to immediately cover all adults and all children through the expanded programme. Even as production volumes are rising, India has to meet international obligations as well. Further, our vaccination teams cannot focus exclusively on Covid vaccination. Routine immunisation of children and pregnant women should not be neglected, as it is a high public health priority that lost ground in the initial stages of the pandemic. Extension of the protective doses to other adults and coverage of younger children can be implemented later when our domestic supplies of Covid vaccines are more abundant and vaccination teams can take up the full range of vaccinations.

This column first appeared in the print edition on December 27, 2021 under the title ‘Putting up a harder fight’. The writer, a cardiologist and epidemiologist, is President, Public Health Foundation of India (PHFI). The views expressed are personal