And the study – which has not yet been peer-reviewed – found that previous infection was associated with an 83% lower risk of reinfection, compared to people who had never been infected before.
But the researchers warned that the protection is not absolute, which means that some people contract the virus again, and it is not clear how long any immunity will last. It is also possible that those with some degree of immunity to the virus will still be able to carry the virus in their noses or throat and thus pass it on to others.
“We now know that most people who have contracted the virus and developed antibodies are protected from reinfection, but this is not completely and we do not yet know the duration of protection,” says Susan Hopkins, senior medical advisor at PHE and colleagues. – The head of the study said in a statement.
“Even if you think you already have the disease and are protected, you can rest assured that you are unlikely to get a severe infection. But there is still a risk that you will catch the infection and pass it on to others,” Hopkins said. .
The SIREN research study regularly tested nearly 21,000 health workers from across the UK between June and November. Among them, 6,614 people have tested positive for the virus, while 14,000 people have not shown signs of previous infection.
But of those infected, 44 of them developed a potential new infection – representing an 83% level of protection against reinfection.
The study will continue to monitor health care workers for 12 months to see if the protection will last longer, but for now, the defined term of protection means that people who caught the virus in the first wave of infection may now be able to catch it again. It will also look at the impact of the new variant and the efficacy of Covid-19 vaccines.
But early insight from the next phase of the study shows that some people with existing immunity carry high levels of the virus and can pass the virus to others.
Hopkins highlighted this during an interview on the BBC’s Today program on Thursday.
“We found people with very high amounts of the virus in their nasal and throat swabs, which could easily be in the range that could cause levels of transmission to other individuals.”
Hopkins stressed that people who have previously contracted Covid-19 still need to comply with social distancing rules to avoid transmitting the disease.
“The SIREN study has major implications for how we can get out of the current crisis. The good news is that this study gives extra weight because re-infection with Covid is rare, at least at this point, and the presence of antibodies will provide protection for a large amount of time,” Although it may not be lifelong immunity, ”Dr. Simon Clark, associate professor of cellular microbiology at the University of Reading, told the Science Media Center.
“The worrying finding is that some people who have antibodies to Covid seem to still be able to carry the Coronavirus and can pass it on to others. This means that the vast majority of the population will either need natural immunity or have been immunized for us. To lift restrictions on our lives completely. “.
Lawrence Young, a virologist and professor of molecular oncology at Warwick Medical School, added that since the results cover the months before the new variant appeared, “it will be important to determine whether previous infection with the old virus variant is able to provide protection from re-infection with the new virus.
England is currently under a strict national lockdown after a spike in cases during the holiday period. The UK has recorded more than 3.2 million cases.