No scientific evidence yet to prove 'Herd immunity' against COVID-19: Lancet

Bhubaneswar: The governments world over have first clamped lockdown to cut the transmission cycle of COVID-19. But now to ease out from the long lockdown situation, which carries a socio-economic impact, a new strategy of developing 'Herd Immunity' to fight COVID is being stressed upon.

It seems the strategy to develop 'herd immunity' has caught the imagination of Odisha Health Department. The technical spokesperson of State Health department Jayant Panda had recently stated that more COVID cases in Odisha will prove helpful in developing 'herd immunity' in the State to fight new COVID wave.

However, a recent study published in Lancet has simply junked the claims of Odisha government that more and more COVID cases in the State will in turn provide 'herd immunity' against future COVID outbreak in the State.

As per the study, the development of IgG antibodies has been detected in around 90 per cent of  COVID patients, who are hospitalised. It further added that even the antibody is not detected in nearly 10 per cent of hospitalised cases.

Moreover, the Lancet study says the key to accomplishing herd immunity lies in development of antibodies in non-hospitalised cases, which means in milder and asymptomatic patients.

The Lancet study, therefore, says, "Anecdotal results from community samples yield estimates of under 10% of tested “controls” developing specific IgG antibodies. So, we await for larger seroprevalence datasets, but it seems likely that natural exposure during this pandemic might, in the short to medium term, not deliver the required level of herd immunity."

Besides, the Lancet study has highlighted another important aspect in the realm of 'Herd immunity'. How long is immunity to COVID-19 likely to last?

The Lancet study says, "The best estimate comes from the closely related coronaviruses and suggests that, in people who had an antibody response, immunity might wane, but is detectable beyond 1 year after hospitalisation."

It then added, " Obviously, longitudinal studies with a duration of just over 1 year are of little reassurance given the possibility that there could be another wave of COVID-19 cases in 3 or 4 years."

The Lancet, therefore, emphasises on the fact of how specific T-lymphocyte immunity against Middle East respiratory syndrome coronavirus can be detectable for 4 years, considerably longer than antibody responses.

Lancet says, "Some of the uncertainty about COVID-19 protective immunity could be addressed by monitoring the frequency of reinfection with SARS-CoV-2. Anecdotal reports of reinfection from China and South Korea should be regarded with caution because some individuals who seemed to have cleared SARS-CoV-2 infection and tested negative on PCR might nevertheless have harboured persistent virus."

It then adds that only virus sequencing studies will help to resolve this issue, and in cases of confirmed reinfection, it will be important to understand if reinfection correlates with lower immunity.

The Bottom line: Lancet, therefore, calls to tread with caution on the concept of 'herd immunity'. For the time being, take all measures to curb its faster transmission.