Extending safety: On deferring second dose of COVID-19 vaccine

Staggering of vaccine doses should not be to merely buy time until more doses are available

Pursuing a policy of spreading the interval between two doses of vaccine, the Centre has now outlined more scenarios of second dose deferment. While lactating women are now encouraged to get vaccinated, those who have recovered from an infection ought to be getting vaccinated three months hence — the recommendation earlier was four to eight weeks. Those inoculated but who have tested positive should defer their second dose by three months after clinical recovery from COVID-19. The recommendations follow from earlier ones that advise increasing the interval from 12-16 weeks for Covishield, the more widely available vaccine. But there are two underlying principles behind these recommendations, the first being a vaccine shortage. Until early April, India had a very different scheme for its vaccination roll-out, appearing to take stock of availability as well as prioritising those at greater disease risk. It was the ferocity of the second wave that caused the government to panic and ‘free up’ vaccine supply applying a ‘to each his own’ approach. While this benefits a fraction of the privileged, it has not improved access as seen by the stagnation in daily inoculations and a fall in second dose recipient numbers.

The second principle is that the timing of the second dose for an optimal boost to the immune system is not clear. A general policy for childhood vaccines in India is a four to eight-week interval. However, clinical trials of the AstraZeneca vaccine in the U.K (18-55 years) showed that binding antibodies (the ones that actually block viruses) were nearly twice as high in those who got their shots 12 or more weeks apart than in doses had within six weeks. The vaccine also appeared to be more protective in those above 18 with a longer dose interval. While antibody levels are a key marker of protection, they are not the only ones. Cell-based immunity, whereby the immune system confers long-lived immunity, counts too. Given that SARS-CoV-2 has been around for less than 20 months, there is uncertainty about the duration of protection. There are also documented cases of breakthrough infections as well as deaths even after a second dose. Though they fall within expected statistical boundaries so far, it is only more inoculations from now that will shed greater clarity on the degree of protection. Put together, these recommendations do buy policy makers time to stagger doses until more vaccines become available from August. On the other hand, the toll from India’s second wave continues to surpass similar daily figures from the U.S. and Brazil. Given that many Indians have still not been exposed to the virus and newer threatening variants abound, there is no reason to be complacent that people will be protected from future waves. The aim of vaccines is to prevent severe disease and death and all policy recommendations must be geared towards that goal. There is no room for knee-jerk reactions that can compromise this objective.

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