Past Covid-19 infection gives at least 5 months of immunity: UK study

People who have been infected with Covid-19 are immune from contracting the virus again for at least five months, according to a major study by Public Health England (PHE), which examined more than 6,500 people between June and December 2020.

The study released on Thursday, however, cautions that those with such immunity may still be able to carry the virus in their noses and throats and therefore pose a risk of transmitting it to others.

PHE scientists working on the study have concluded that naturally acquired immunity as a result of past infections provide 83% protection against reinfection, compared to people who have not had the disease before.

PHE said that the study called SIREN (SARS-CoV-2 Immunity and Reinfection EvaluatioN) will continue to assess whether protection may last for longer, which means that people who contracted the disease in the first wave may now be vulnerable to catching it again.

Between June 18 and November 24, scientists detected 44 potential reinfections (2 ‘probable’ and 42 ‘possible’ reinfections) out of 6,614 participants who had tested positive for antibodies. This represents an 83% rate of protection from reinfection, PHE said.

Susan Hopkins, SIREN study lead, said: “This study has given us the clearest picture to date of the nature of antibody protection against Covid-19 but it is critical people do not misunderstand these early findings”.

“We now know that most of those who have had the virus, and developed antibodies, are protected from reinfection, but this is not total and we do not yet know how long protection lasts. Crucially, we believe people may still be able to pass the virus on”.

She added: “This means even if you believe you already had the disease and are protected, you can be reassured it is highly unlikely you will develop severe infections but there is still a risk that you could acquire an infection and transmit to others.”

PHE said the study will continue to follow participants for 12 months to explore how long any immunity may last, the effectiveness of vaccines and to what extent people with immunity are able to carry and transmit the virus.