Can one be reinfected with Covid? No evidence so far, say experts

they produced more neutralising antibodies which protected them against short-term reinfection.

“There is experimental evidence from monkeys that once infected, there is resistance to reinfection. In humans, reinfection has not been observed in recovered patients, many months since the first wave of infections. We do not know that this is attributable to antibodies, but rise of antibodies is correlated to disappearance of the virus. So, there is a reason to believe that recovery is associated with gaining at least short-term immunity; antibodies contribute to such immunity, and antibodies are not the full story,” said Dr Anurag Agrawal, director, Institute of Genomics and Integrative Biology (Council of Scientific and Industrial Research, Delhi.

Studies have found that levels of neutralising antibodies that bind to the new coronavirus viral proteins to directly prevent infection remain high only for a few weeks, after which it begins to fall. Antibodies last at higher levels for longer in people who had severe disease, compared to those with mild or asymptomatic disease, which has led to concerns that those with mild disease may not have lasting protecting against Covid-19.

This follows a pattern similar to other coronavirus diseases, such Sars (severe acute respiratory syndrome).

What is known about SarsCOV-2 infection is that no reinfection has been reported. “No evidence of reinfection has been validated, and theories on when antibodies in people with mild and asymptomatic disease disappear are pure guesswork. The few reported cases were misrepresentation. They found traces of viral genetic material (RNA) in nasal swabs, which may have been a remnant of natural infection before recovery...when the viral load is low and there is no transmission, it is of no epidemiological significance as the person doesn’t infect others,” said Dr T Jacob Jon, virologist and professor at Christian Medical College, Vellore, Tamil Nadu.

The levels of neutralising antibodies needed to prevent reinfection or reduce symptoms in a second illness is also unclear. “Most mutating viruses need repeat vaccination. This is mutating slower than expected but it seems unlikely that there will be a one-time only vaccine,” said Dr Agrawal.

A c o mp a r i s o n o f the i mmune r e s ponses o f 3 7 asymptomatic patients to an equal number of severely ill patients in China showed asymptomatic people reacted less strongly to infection, 40% of asymptomatic patients losing their IGG protective antibodies within a few weeks or months after recovery, within two to three months after the infection compared to 12.9% of the symptomatic patients, reported a study published in Nature Medicine on June 18.

“Sero-surveillance helps predictions and policy. For the person tested, it is likely that those who have antibodies are recovered and have lower risk. However, this is not proven and antibody positivity does not equal immunity in many diseases. This may be resolved by testing for neutralising antibodies but it is possible that even those without neutralising antibodies may have antibody-independent immune resistance acquired during infection,” said Dr Agrawal.