Recovered COVID-19 patients may be protected, but they could still transmit the virus

A new study has shown that while patients who have recovered from COVID-19 are likely to be protected against reinfection for several months, they may still be able carry the virus in their nose and throat, transmitting it to others.

Since June 2020, Public Health England (PHE) has been performing regular antibody and polymerase chain reaction (PCR) testing on 20,787 healthcare workers, including frontline clinical staff and those in non-clinical roles, to study how long immunity following infection may last.

The scientists working on this study, called SIREN (SARS-CoV-2 Immunity and Reinfection EvaluatioN), detected 44 potential reinfections (2 ‘probable’ and 42 ‘possible’ reinfections) out of 6,614 participants who had tested positive for antibodies between June and November 2020. This suggests naturally acquired immunity as a result of past infections provides 83 percent protection against reinfection, compared to people who have not had the disease before. According to their data, this appears to last at least five months from first signs of illness.

While the SIREN study will continue to assess whether protection may last for longer, the investigator cautions that if protection only lasts a limited time, people who contracted COVID-19 in the first wave may now be vulnerable to reinfection.

The next stage of the study will evaluate whether people who have recovered from COVID-19 could still carry and transmit the SARS-CoV-2 virus which causes it. However, PHE warned that early evidence suggests that some individuals carrying high levels of virus and could continue to transmit the virus to others, even though they have immunity themselves.

As such, PHE said it is essential for people to follow the rules regarding face masks and social distancing, even if they have previously had COVID-19, to prevent spreading the virus to others.

Professor Susan Hopkins, Senior Medical Advisor at Public Health England and the 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.

“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. Now more than ever it is vital we all stay at home to protect our health service and save lives.”

PHE added that this analysis occurred prior to the widespread dissemination of the new, highly infectious SARS-CoV-2 variant VOC202012/01, so further work is currently being undertaken to establish whether, and to what extent, antibodies also provide protection from this variant. It said future analysis would also assess the impact of VOC202012/01 on symptomatic and asymptomatic infections in healthcare workers.

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.