England Reports Optimistic COVID-19 Reinfection Rates

People infected with COVID-19 in the past are likely to be protected against reinfection for several months, a Public Health England (PHE) study has found.

However, United Kingdom (UK) experts are cautioning that those with immunity may still be able to carry the SARS-CoV-2 coronavirus in their nose and throat and, therefore, risk transmitting the virus to others.

PHE announced on January 14, 2021, it has been regularly testing tens of thousands of health care workers across the UK since June 2020 for new COVID-19 infections. PHE scientists working on the SARS-CoV-2 Immunity and Reinfection EvaluatioN (SIREN) study have concluded that naturally acquired immunity resulting from past infections provides 83 percent protection against reinfection to people who have not had the disease before.

This appears to last at least 5 months from first becoming sick.

While the SIREN study will continue to assess whether protection may last longer, this means people who contracted COVID-19 in the first wave may now be vulnerable to catching the virus again.

PHE also warned that although those with antibodies have some protection from becoming ill with COVID-19 themselves, early evidence from the next stage of the study suggests that some of these individuals carry high levels of virus and could continue to transmit the virus to others.

‘It is therefore crucial that everyone continues to follow the rules and stays at home, even if they have previously had COVID-19, to prevent spreading the virus to others. Remember to wash hands regularly, wear face coverings, and make space from others to help reduce the likelihood of passing on the virus', says the PHE press statement.

Professor Susan Hopkins, a Senior Medical Advisor at PHE and the SIREN study lead, added, ‘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 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 it to others. Now more than ever, it is vital we all stay at home to protect our health service and save lives,’ concluded Hopkins.

PHE’s SIREN study has performed regular antibody and PCR testing on 20,787 healthcare workers, including frontline clinical staff and those in non-clinical roles, from 102 NHS trusts since the study commenced in June 2020.

Of the 44 potential reinfections identified by the SIREN study, 2 were designated ‘probable’ and 42 ‘possible,’ based on the amount of confirmatory evidence available. If all 44 cases were confirmed, it would represent an 83 percent protection rate from reinfection, while if only the 2 ‘probable’ reinfections were confirmed, the rate would be 99 percent.

Further research is ongoing to clarify this range, said PHE.

Both of the 2 ‘probable’ reinfections reported having experienced COVID-19 symptoms during the first wave of the pandemic but were not tested at the time. Both patients reported that their symptoms were less severe the second time.

None of the 44 potential reinfection cases were PCR tested during the first wave, but all tested positive for COVID-19 antibodies at the study's point of recruitment.

Separately, Eleanor Riley, Professor of Immunology and Infectious Disease, University of Edinburgh, commented in a Science Media article, “The take-home message from this study is that primary infection with SARS-CoV-2 provides at least 94% protection against symptomatic reinfection for at least five months.”

“This suggests that natural infection provides short-term protection against Covid-19 that is very similar to that conferred by vaccination.”

“Importantly, natural infection induces approx. 75% protection against asymptomatic reinfection, suggesting that people who have recovered from SARS-Cov-2 infection are much less likely to transmit the virus to others.”

“This is good news in terms of the long term trends of the pandemic. However, asymptomatic reinfections are not zero, so you cannot assume that you can’t be infectious just because you have had the virus before that.

“These data reinforce the message that, for the time being, everyone should consider themselves to be a potential source of infection for others and should behave accordingly,” concluded Riley.

Note: This analysis of the SIREN study occurred before the widespread dissemination of the new variant VOC202012/01, further work is underway in the laboratory to understand whether and to what extent antibodies also provide protection from this variant, and future analysis will assess the impact of VOC202012/01 on symptomatic and asymptomatic infections in healthcare workers.

The SIREN study will continue to follow participants for 12 months to explore how long any immunity may last, the effectiveness of vaccines, and the extent to which people with immunity can carry and transmit the virus, stated PHE.

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