Covid infection provides immunity for at leasdt five months, according to a new study led by Public Health England (PHE).
Findings magnified the link between past infection and an 83% lower risk of reinfection, compared to people who have not been contracted the virus before.
However, researchers stressed that the protection was not absolute, meaning some individuals can be infected again and that how long any immunity lasts remains uncertain. People who have a degree of immunity against the virus could still carry the virus in their nose or throat and infect others.
"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," Susan Hopkins, senior medical adviser at PHE and co-leader of the study, said in a statement.
"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 you could acquire an infection and transmit (it) to others," Hopkins said.
The SIREN research study constantly tested 21,000 health workers from across the UK between June and November. Meanwhile, 6,614 participants tested positive for antibodies against the virus, while over 14,000 did not show symptoms of any previous infection.
However, those who had contracted the virus, 44 manifested possible new infections -- representing an 83% level of protection against reinfection.
The PHE study will regularly monitor healthcare workers for 12 months to determine if protection could last longer, but for now, the length of protection suggests that individuals who contracted the virus may now be able to catch it again. It will also examine the impact of the new variant and the effectiveness of coronavirus vaccines.
An early look into the next stage of the study reveals that some people with existing immunity have high levels of virus and could pass it to others.
"We found people with very high amounts of virus in their nose and throat swabs, that would easily be in the range which would cause levels of transmission to other individuals,” Hopkins said.
He explained that people who had caught Covid-19 must observe social distancing protocols to avoid carrying the virus.
"The SIREN study has major implications for how we can get out of the current crisis. The good news is that this study gives further weight that reinfections of Covid is rare, at least at this stage, and that having antibodies will provide protection for a meaningful amount of time, although it may not be lifelong immunity," Dr. Simon Clarke, Associate Professor in Cellular Microbiology, University of Reading, told the Science Media Centre.
"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 immunized for us to fully lift restrictions on our lives," he said.
Meanwhile, Lawrence Young, Virologist and Professor of Molecular Oncology, Warwick Medical School explained that "it will be important to determine whether the previous infection with the old virus variant is able to offer protection from re-infection with the new virus variant."
