It may affect the optimal use of the vaccine that is being conserved for specific populations
As Kerala is preparing to roll out the COVID-19 vaccine, lack of seroprevalence data, either amongst the population or the subgroup of health-care workers in the State, is likely to indirectly affect the optimal use of the vaccine, which is being conserved for specific at-risk populations.
Despite recommendations from various public health experts and the State-appointed expert committee on COVID-19, the government appears disinclined to conduct a seroprevalence study across the State or among the health-care workers. While official estimates put the affected State’s population at just 6.3 lakh, a seroprevalence study would reveal the real extent of the spread of the virus in the community and the proportion of the population which might have had prior and silent exposure to the virus. A serial survey would have helped the State monitor the trend of infection in the general population, determine the socio-demographic risk factors and assess the geographical spread of the infection.
The Centre has made it clear that at least for the time being, universal vaccination would be impossible and it is likely to be restricted to priority groups, with the health workers coming at the top. However, it is highly likely that a chunk of the workers, because of their regular interactions with patients and visitors in hospitals, would have already been exposed to the virus and might have developed natural immunity against SARS-CoV-2.
According to virologist T. Jacob John, “SARS-CoV-2 is not an anomalous virus capable of miraculous feats of immune evasion… and it is not invulnerable to our immune defences… and even when antibodies wane, protective immunity after the first infection is probably durable”.
“The SARS-CoV-2 seroprevalence data become very important when it comes to prioritising vaccine for non-immune, high-risk groups like healthcare workers because those who have had prior infection would be already protected. There have been several studies (Birmingham University/Karolinska Institute studies) which proved that even a mild or even asymptomatic infection by SARS-CoV-2 can render robust T-cell immunity, which lasts for over six months,”a public health expert points out.
Proper seroprevalence survey, at least among the health workers, would have answered two questions: whether the health-care workers are the actual vulnerable, non-immune group in the State which needs the vaccine on priority and secondly, what is the proportion of this population which is yet to be exposed to COVID-19 and hence should be administered the vaccine on priority.
“As a general policy, the government can choose the health-care workers as a priority group. But if seroprevalence data are available, the State could optimally utilise the vaccine, which would initially be available only in limited quantities,” he said
In the absence of easy and affordable tests to detect T-cell immune response to SARS CoV-2, seroprevalence studies to measure antibody response to the virus in blood would be the best bet to confirm past COVID infection.
However, public health experts point out that the State’s epidemic curve having crossed the peak in October, the State might have left it too late to conduct the survey. Because the antibody levels in blood, indicative of virus exposure, generally tend to wane within three months. Hence, any surveys done now would not be time-appropriate and will be an underestimation of the true picture of the infection in the State.