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LONDON — People who have been infected with Covid are likely to have some form of immunity for at least five months, according to early results of a major new study in the U.K.
The preliminary findings in Public Health England’s SIREN study — which has surveyed thousands of U.K. health-care workers in a bid to establish whether prior infection protects against future infection — found antibodies provide an 83% rate of protection against reinfection, compared with people who have not had the disease before.
This immunity appears to last at least five months, the report said. Reinfections in people with antibodies were rare, the study published on Thursday found, with experts identifying 44 potential reinfections among 6,614 participants involved the study.
However, the early evidence also suggests a small number of people with antibodies may still be able to carry and transmit the virus, emphasizing the need to follow coronavirus restrictions, Public Health England said.
The study has not yet been peer-reviewed or published in any medical journal; its authors stress the results are an interim analysis of data collected between June and November. So the research was undertaken prior to the dissemination of the new variant in the U.K.
Susan Hopkins, a senior medical advisor at Public Health England and the SIREN study lead, said the research “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,” she added. “Now more than ever it is vital we all stay at home to protect our health service and save lives.”
The study comes as coronavirus vaccines developed by Pfizer–BioNTech, Moderna and the University of Oxford and AstraZeneca are being rolled out in the U.K.; the former two vaccine candidates were found to be around 95% at preventing Covid-19 infection, and the latter candidate 70% effective on average.
Scientists are still uncertain as to how long the protection from coronavirus vaccines might last. They are also unsure as to whether a vaccinated person will still be able to transmit the virus.
The SIREN study leaders stressed that this preliminary report “provides no evidence towards the antibody or other immune responses from Covid-19 vaccines, nor should any conclusions to be drawn on their effectiveness,” adding that it will consider vaccine responses later this year.
The study will continue to assess whether protection may last for longer, with Public Health England cautioning that the results mean that people who contracted the disease in the first wave may now be vulnerable to catching it again.
The SIREN study, which stands for SARS-CoV-2 Immunity & Reinfection Evaluation and started in June, has performed regular antibody and PCR testing on 20,787 health workers, including frontline clinical staff and those in nonclinical roles.
Participants attended regular testing every two to four weeks and completed fortnightly questionnaires on symptoms and exposures to the virus.
Of the 44 potential reinfections identified by the study, two were designated “probable” and 42 as “possible”: The term “potential reinfections” is used because none of the 44 potential reinfection cases were PCR tested during the first wave of the pandemic, but all tested positive for Covid antibodies at the point of recruitment to the study, it noted.
Having found that antibody protection after infection lasts for at least five months on average, scientists are studying whether protection may last for longer.
This analysis occurred prior to the widespread dissemination of the new variant of the virus reported by the U.K. in December, as well as another variant found in South Africa. PHE said “further work is underway in the laboratory to understand whether and to what extent antibodies also provide protection from this variant.”
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, it added.