Covid infection provides some immunity for at least five months, UK study finds
Patients arrive in ambulances at the Royal London Hospital, on January 05, 2021 in London, England. The British Prime Minister made a national television address on Monday evening announcing England is to enter its third lockdown of the covid-19 pandemic. This week the UK recorded more than 50,000 new confirmed Covid cases for the seventh day in a row.Dan Kitwood | Getty Images News | Getty ImagesLONDON — People who have been infected with Covid-19 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.
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 to people who have not had the disease before.
This naturally-acquired immunity appears to last at least five months, the report stated. 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 current 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The study has not yet been peer-reviewed or published in any medical journal; its authors stress the results are an interim analysis of data collected between June and November 2020.
Professor 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. Now more than ever it is vital we all stay at home to protect our health service and save lives," she added.
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.
As with naturally-acquired immunity, 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 PHE cautioning that the results mean that people who contracted the disease in the first wave may now be vulnerable to catching it again.
The study
The SIREN (SARS-CoV-2 Immunity & Reinfection EvaluatioN) study performed regular antibody and PCR testing on 20,787 health care workers (including frontline clinical staff and those in non-clinical roles) since the study commenced in June.
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-19 antibodies at the point of recruitment to the study, it noted.
VIDEO2:5402:54Cautiously optimistic on China's steady growth as virus concerns remain: AnalystStreet Signs AsiaHaving found that antibody protection after infection lasts for at least five months on average, scientists are currently 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. 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.