Immunity against coronavirus post-infection could be short-lived, indicate British, Chinese studies

Reliance on ‘herd immunity’ tricky, antibody levels fall sharpest among asymptomatic

Desperate to curb the Covid-19 pandemic spiraling out of control, governments are now banking on herd immunity. But how viable is this when a recent longitudinal study has indicated that the immunity could be short-lived? Even a single-shot vaccine may not be enough, the study cautioned.

Here’s what repeated testing of 96 Covid-19 patients and health-care workers by researchers at King’s College London showed: The virus-fighting antibodies peaked about three weeks after symptoms showed up, and then vanished rapidly. An earlier Chinese study had shown similar results.

For the longitudinal study, 60 per cent of the patients tested while they had Covid-19 were seen to have produced the antibodies that were dubbed ‘potent.’ But at the end of the three-month testing period, only 17 per cent recorded the same level of potency, stated the study findings posted recently in the MIT Technology Review.

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Antibody levels were found to be higher and lasting longer in patients with more severe Covid-19 cases. However, the study did not detect any antibodies in some milder cases at the end of the three months. The findings will now have to be peer-reviewed.

Similar studies in India on immunity could build prove conclusive. But the King’s College findings have raised the prospect that Covid-19 could re-infect people repeatedly. “If that’s the case, ‘herd immunity’ may never arrive, either through a one-shot vaccine or through community spread of the virus, as any protective antibodies would wane with time,” the Review observed.

On June 18, a Chinese study published in Nature Medicine, had recorded that antibody levels found in recovered Covid-19 patients fell sharply within two to three months post-infection. This trend was seen in both symptomatic and asymptomatic patients. Questions were raised about the length of any immunity against the virus.

The study had covered 37 symptomatic and 37 asymptomatic patients. Among those who tested positive for the IgG antibody (a key type inducted post-infection), more than 90 per cent recorded a sharp decline within two to three months.

It was also found that asymptomatic carriers of the virus had significantly lower levels of antibodies than symptomatic patients during active infection. Eight weeks after recovery, 40 per cent of the asymptomatic patients had no detectable antibodies. Even for symptomatic patients, the levels reduced to 13 per cent.

The findings of both the Chinese and King’s College have brought the reliance on ‘herd immunity’ as a ploy to combat Covid-19 into serious question. Herd immunity presumes that once a sufficient section of the population (threshold proportion) turns immune to the disease, the spread of the disease from person to person would be unlikely.