India's healthcare system has delivered 1 billion doses of COVID vaccines - one dose cover for 52 per cent of the total population but two dose cover only for 22.5 per cent. This triumphant moment also calls for calm reflection and planning the next moves.
COVID has become endemic in India, with daily new cases fewer than 20,000, a fact acknowledged by Dr Soumya Swaminathan, Chief Scientist, World Health Organization (WHO). Also, active cases (source of infection) are now less than 2,00,000 and steadily falling.
During the endemic phase, the proportion of non-immune susceptible people will be small, but reinfections (in those previously infected) and breakthrough infections (in those who had received two doses of vaccine) will rise; eventually, breakthrough infections will outnumber reinfections (immunity is stronger after infection than after a two-dose vaccination).
However, the recent trend in India's mortality curve is disturbing - daily deaths that reached a nadir of 176 on October 21 have almost tripled in the last seven days to 593, but daily new cases remain stationary (15,108 vs 14,727). Unless we administer booster doses to the elderly and vulnerable (with waned immunity after two doses of vaccine), this trend of increasing serious COVID, hospitalisation and death will continue. Recently, two eminent personalities (Colin Powell in the US and a senior cardiologist in India) lost their lives to COVID despite two doses, illustrating this problem.
The WHO's interim report on October 4 cautioned against a booster. But a week later, the Strategic Advisory Group of Experts (SAGE) on Immunization recommended a booster for the moderately or severely immunocompromised individuals - making a clearly visible shift in recommendation.
The booster dose of all common vaccines, ideally given six months or more after the priming doses, induce a brisk and durable antibody response. A COVID booster will probably be no exception. A large, controlled clinical trial (yet to be peer-reviewed) done recently by Pfizer in those above the age of 18 showed that a booster 11 months after the second dose prevented breakthrough infections (including that of the Delta variant) by 95.6 per cent - which will translate into less frequent severe COVID and lower mortality.
In India, an ICMR study showed that more than 80 per cent of breakthrough infections are due to the Delta variant. Also, a study of vaccinated healthcare workers at CMC, Vellore, showed that two doses of the current COVID vaccines gave only 36 per cent protection.
Two groups deserve special focus. Vaccinated healthcare workers, at high risk for breakthrough infections because of occupational exposure to coronavirus; the elderly and vulnerable in households with school-going children (with the reopening of schools, unvaccinated children are likely to bring the prevailing variant home). A booster dose for such people is a necessary life-saving preventive measure.
The magnitude and durability of the immune response to a booster dose of Covaxin are being studied in Indian subjects (results yet to be published). Whether a third dose of Covishield as a booster will elicit a brisk response is yet to be studied as the immune system exposed to the carrier adenovirus twice earlier may mount an immune response to the adenovirus and mute the response to the coronavirus spike protein.
However, with the sharp uptick in COVID mortality in India, there is an urgent need to start giving booster doses to those at high risk. It will be unethical to have a control group without the benefit of a booster; this may result in serious disease or death.
Healthcare workers above age 65 and those even younger but with a comorbidity should be offered the booster. Prospective follow-up will be easier in this group and inform us about the efficacy and safety outcomes after a booster dose.
Unvaccinated elderly and vulnerable (including healthcare workers) who had previous infections and have not had a vaccine dose should get a single jab. Those who had COVID followed by one or two vaccine doses and those who had two doses of vaccine followed by a breakthrough infection will already have boosted immunity (combined response to infection and vaccine) and hence would not need an additional dose at present. A random sample of such subjects should be studied to assess the durability of the immunity. This will help us plan the future course of action.
The US FDA approved mixing of mRNA vaccines for the booster shot for eligible subjects. This means those who received two doses of Pfizer vaccine can opt for Moderna as the booster.
An inadvertent vaccine mix-up in UP (where 18 subjects had Covishield as the first shot and Covaxin for the second dose) studied by the ICMR demonstrated a better immune response than two doses of Covishield. This serendipitous observation, albeit in a small group, supports the use of Covaxin as a booster in those who had two doses of Covishield earlier. Standard practice dictates Covaxin booster for those with primary Covaxin doses.
Booster doses need only a revision of policy since both vaccines have Emergency Use Authorisation. The government needs to take a nuanced stand: the endemic state of COVID in India, vaccine availability and number of breakthrough infections causing severe disease should dictate policy. With improved vaccine availability, booster doses for the elderly and vulnerable can be undertaken concurrently with the second dose for those who had only one jab.
India needs to learn to live with endemic COVID and this demands two policy shifts. One, begin vaccinating children as early as possible to reduce the size of the virus reservoir (see Why we need to vaccinate our kids against COVID, Oct 23) and two, administering booster shots as described above. The study of durability of immunity will guide plans for the need, if any, and timing of subsequent booster(s) in the elderly, vulnerable and eventually, the entire population.
(Dr MS Seshadri is medical director, Thirumalai Mission Hospital, Ranipet and can be contacted at mandalam.seshadri@gmail.com)
(Dr T Jacob John is former professor of clinical virology, CMC, Vellore and can be contacted at tjacobjohn@yahoo.co.in)