Infection with the SARS-CoV-2 virus may provide some immunity for at least 5 months, interim results from a study has found.
The first report from the Sarscov2 Immunity & Reinfection Evaluation (SIREN) study suggested that antibodies from people who had recovered from COVID-19 gave at least 83% protection against reinfection compared with people who had not had the disease before.
However, Public Health England (PHE) researchers said some people with antibodies may still be able to carry and transmit the SARS-CoV-2 virus.
Susan Hopkins, PhD, senior medical advisor at PHE, who is leading the study, said the overall findings were good news. She told a briefing hosted by the Science Media Centre: “I am strongly encouraged that people have immunity that is lasting much more than the few months that was speculated before the summer.”
She added: “It allows people to feel that their prior infection will protect them from future infections but at the same time it is not complete protection, and therefore they still need to be careful when they are out and about.”
PHE scientists said they would continue to assess whether protection might last longer than 5 months.
Eleanor Riley, PhD, professor of immunology and infectious disease at the University of Edinburgh, said the report suggested that “natural infection provides short-term protection against COVID-19 that is very similar to that conferred by vaccination.”
Simon Clarke, PhD, associate professor in cellular microbiology at the University of Reading, said: “The concerning finding is that some people who have COVID antibodies appear to still be able to carry the coronavirus and could spread it to others. This means that the vast majority of the population will either need to have natural immunity or have been immunised for us to fully lift restrictions on our lives.”
The analysis took place before the new variant of SARS-CoV-2 became widespread in the UK. The PHE scientists said that further work was underway to establish whether and to what extent antibodies also provide protection from the VOC202012/01 variant.
The SIREN preprint analysed data from 20,787 health care workers from 102 NHS trusts who had undergone antibody and PCR testing from June 18 to November 9, 2020.
Of those, 6614 tested positive for COVID-19 antibodies.
Of the 44 potential reinfections identified, two were designated ‘probable’ and 42 ‘possible’, based on available evidence.
Both of the two individuals classified as probable reinfections reported having experienced COVID-19 symptoms during the first wave of the pandemic but were not tested at the time. Both 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 time they were recruited to the study.
Tom Wingfield, PhD, senior clinical lecturer at the Liverpool School of Tropical Medicine, said that given the high risk of SARS-CoV-2 infection for frontline NHS staff, it was “vital that we do all that we can to understand, predict, and prevent risk of SARS-CoV-2 amongst 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.
A version of this article first appeared on Medscape.com.