India is currently dealing with the second wave of COVID-19. As cases surge, a question that is often asked by people who had contracted the virus and recovered from it is - how long does natural immunity against coronavirus last?
According to research by the Institute of Genomics and Integrative Biology (IGIB), natural immunity against COVID-19 lasts for 6 to 7 months. It also states that between 20-30% of those infected with the virus shed this immunity after a 6-month period.
"The key finding of 20-30% of subjects losing virus neutralizing activity, despite staying seropositive, at 6 month follow-up helps understand why the large second wave has not spared cities like Mumbai with high seropositivity," Dr Anurag Agarwal, the director of IGIB stated on Twitter.
The findings of this research are particularly important for India as they could potentially explain the timing of the second wave of the COVID-19 pandemic in the country. The results also emphasise the importance of vaccination against virus infection.
Research on the immunity period of COVID-19 vaccines is still ongoing, but most vaccines currently in use are expected to protect beneficiaries from severe coronavirus infection or death for at least a couple of years.
Researchers have stated that the findings can explain why cities like Mumbai and Delhi are experiencing a spike in COVID-19 cases. This is happening despite these cities having high seropositivity, according to Hindustan Times. Delhi had average seropositivity of just over 56 per cent in January. Many doctors attributed Delhi's seropositivity as the reason behind the slowdown of the COVID-19 pandemic surge in November 2020.
The IGIB study established that seropositivity was inversely proportional to the test positivity rate of COVID-19.
"In September, when we conducted a sero-survey across CSIR (Council for Scientific and Industrial Research) laboratories, just over 10% of the participants were found to have antibodies against the virus. Then, we followed up with a fraction of these participants for three and five to six months and conducted a quantitative test to check their antibody levels," said Dr Shantanu Sengupta, according to the daily. Sengupta is a senior scientist from IGIB and one of the writers of the study which was published in eLife journal on April 10. "At five to six months, nearly 20 per cent of the participants had lost the neutralisation activity despite having antibodies; the neutralisation activity for the rest was also on the decline."
Nearly 10 per cent of the participants of the study tested positive for antibodies in September 2020. The researchers tracked 175 of these participants for a period of five to six months and discovered that 31 of them had lost the neutralising activity and eight of them no longer had antibodies.