The Problems With One-Dose Covishield

If Covishield is administered as a single-dose vaccine, a small study found its efficacy against symptomatic COVID-19 caused by the B.1.617.2 variant is only 33%.

On May 31, NDTV quoted unnamed sources in the Indian government saying it will be conducting a study to assess the feasibility of deploying the Covishield vaccine as a single dose instead of continuing the double-dose regimen.

At any other time, such a statement may have been sufficient to believe the government would organise and conduct a well-designed trial, publicise the findings and revise policy (or not) to stay in line with the findings, informed by socio-economic considerations. But the past 15 months have thrown up enough incidents of public-health malpractice on the state’s part to make such hope foolish. There is a nontrivial chance, especially if the vaccine shortage persists and the outbreaks on an upward trajectory in some parts of the country at the moment aren’t tamped down quickly, that the government is going to conduct a trial, not publish its methods and findings and push through a policy to deploy Covishield as a single-dose shot.

The prospects of this outcome should suffice to sadden us. By just considering the possibility of using Covishield as a single-dose vaccine, the government seems set on finding new ways to enhance its reputation at the cost of public health.

News that the government is going to conduct a feasibility study broke to the accompaniment of a suggestion, by the same unnamed sources, that Covishield was originally intended as a single-dose vaccine and that it was later found to be better as a two-dose vaccine. This is a ridiculous claim, considering Covishield’s phase 3 trials around the world, conducted by AstraZeneca and the University of Oxford, tested the two-dose regimen.

But it is rendered more ridiculous because Public Health England (PHE) reported just a week ago that two doses of Covishield are necessary for a recipient to be sufficiently protected against infections by the B.1.617.2 variant. The PHE study found that one dose of Covishield had an efficacy of 33% against symptomatic COVID-19 caused by the variant, increasing to 60% after both doses. Has the Indian government forgotten that B.1.617.2 is becoming the more common variant circulating in the country? Or is laundering the national party’s image more important than the safety of hundreds of millions?

(The latter is entirely plausible: in the last seven years, the country has seldom been larger than the supreme leader’s ego.)

The PHE study isn’t without its shortcomings. However, a lot of other important data we need to make informed decisions at this time is missing, read together with the Central government’s obfuscatory tendencies during the COVID-19 pandemic. Missing from the public domain:

1. Covaxin’s phase 3 trial (which reportedly went past its final interim-analysis endpoint in April)

2. Covishield’s bridging trial (which concluded in late March 2021, according to the trial registration)

3. Large-scale effectiveness data of the two vaccines (the National Institute of Epidemiology, Chennai, is set to begin collecting such data this week); and

4. Any other reliable data about the two vaccines vis-à-vis the different variants circulating in India

There is another problem. If Covishield is administered as a single-dose vaccine, its efficacy against symptomatic COVID-19 caused by B.1.617.2 viral particles is 33% – which is below the WHO’s recommended efficacy threshold of 50% for these vaccines. If the Indian government formalises the ‘Covishield will be one dose’ policy and if the B.1.617.2 variant continues its conquest, will the vaccine, as it is used in India, lose its place on the WHO’s vaccine list? And what of the consequences that will follow, including other countries becoming reluctant to admit Indians who received one dose of Covishield and one dose of India’s way of doing things?

There would be cause for wariness. The longer the novel coronavirus is able to circulate within a population, the more opportunities it will have to mutate, and the more mutations it will accumulate. So any population that allows the virus to persist for longer automatically increases the chance of engendering potentially deadlier variants within its borders. One-dose Covishield plus B.1.617.2, and other variants, will set just such a stage – compounded by the fact that Serum Institute, which makes Covishield, has a much larger production capacity than Bharat Biotech, the maker of Covaxin.

(The PHE study also found that a singe dose of Covishield and the Pfizer-BioNTech vaccine had an efficacy of “around 50%” against symptomatic COVID-19 caused by an infection of the B.1.1.7 variant.)

In fact, the government could have made more sense by saying it would prioritise the delivery of the first dose to as many people as possible before helping people get the second one. This way the policy would be in line with the most recent scientific findings, be synonymous with a single-dose campaign and keep the door open to vaccinating people with both doses in a longer span of time (instead of closing that door entirely), while admitting that the vaccine shortage is real and crippling – something most of us know anyway. But no; it appears to have put something other than public health first.

This article was originally published on the author’s blog, and has been published here with edits for clarity and style.