Seronegative-first plan makes better Covid-19 vaccine sense, suggests study

Will those exposed to the novel coronavirus be given the shots when the Centre rolls out the Covid-19 vaccination campaign?

While the government is yet to take a call on such a critical issue, a new study has shown that preferentially vaccinating seronegative individuals — who were not exposed to the virus and who tested negative in antibody tests — yielded large additional reductions in cumulative incidence and mortality.

The modelling study concluded that while vaccinating 60-plus individuals was indeed a robust strategy, picking those who were not exposed to the virus for the jab would lead to a substantial reduction in the cumulative incidence and mortality in areas with high seroprevalence and modest reductions in locations with low seroprevalence.

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Carried out by researchers from the University of Colorado, Boulder; Harvard T H Chan School of Public Health and the University of Chicago, the study — not yet peer-reviewed — has been released in a preprint server for its importance.

"We found that across countries, those 60 years and older should be prioritised to minimise deaths, assuming a return to pre-pandemic behaviour during or after vaccine rollout. This recommendation is robust because of the dramatic differences in infection fatality rate by age," they reported.

"We also suggest that after distribution pairing serological testing with vaccination in the hardest-hit populations is a possible equitable way to extend the benefits of vaccination in settings where vaccination might otherwise not be deemed cost-effective."

The researchers, however, admitted that the strategy comes with an implementation challenge.

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"A mathematical modelling by a team of scientists in the US has now predicted the usefulness of vaccinating antibody-negative individuals first. Their data is excellent. We can defer vaccination of antibody-positives," commented Abdul Ghafur, a consultant in infectious diseases, Apollo Hospital, Chennai, who is not associated with the study.

Asked whether vaccination would be preceded by a blood test to check the presence of Covid-specific antibodies in the recipient’s body, Union Health Secretary Rajesh Bhushan said, "It is an issue before the national expert group of vaccination, but there is no final decision."

Officials said that while measuring antibodies could spare the vaccines for those who were vulnerable, there was no evidence on how long such protection would last.

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"There is no evidence regarding the usefulness of giving vaccines to those who are already infected. If about 50% of people are infected already, we don’t know whether they would need vaccination, and if yes, one or two doses... There is no evidence if antibody testing ahead of vaccination can be cost-effective,” said Giridhar Babu, an epidemiologist at the Public Health Foundation of India.

An Indian supermodel on Covid-19 — created by a group of scientists put together by the Department of Science and Technology — has predicted that nearly 50% of Indian population has been exposed to the virus by December 13 even though they have little or no symptoms.

"Most states have crossed the 50% mark. There was a slight uptick in November due to a rise in people's interaction. The curve has started going down again and we are unlikely to see another peak due to a large number of people with antibodies," mathematician Manindra Agarwal, dean at IIT Kanpur and a member of the DST team, told DH.