Catching coronavirus gives 83% protection against reinfection for up to 5 months, a study suggests – but you could still spread the virus

• Catching coronavirus gives you about 83% protection from reinfection for up to five months, a large preliminary UK study suggests.
• This is comparable to the protection offered by vaccines.
• Work is ongoing to find out how long immunity lasts, whether vaccines work in people previously infected, and if people with immunity can pass on the virus.
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Catching coronavirus once makes it highly unlikely you’ll catch it again for up to five months, and the protection is comparable to a COVID-19 vaccine, a large preliminary study of health workers suggests.

Public Health England’s “SIREN” study  involved 20,787 people from across the UK’s National Health Service. It found that only 44 out of 6,614 participants who had antibodies – suggesting previous COVID-19 infection – were potentially reinfected over five months.

Researchers said that overall, antibodies gave subjects about an 83% protection rate from reinfection. This compares to roughly 95% protection after immunization with Pfizer and BioNTech or Moderna’s COVID-19 vaccines.   

Study lead Susan Hopkins, senior medical advisor at Public Health England, said in a statement that the study provided “the clearest picture to date” of whether antibodies protect against COVID-19. 

The participants had blood tests for antibodies against coronavirus, and swab testing for the virus itself at one-to-four weekly intervals between June 18 and November 24, per the study protocol.

Tang said that the results were not surprising, because we already knew that other coronaviruses produce long-lasting antibodies. Antibodies to the seasonal common cold last for 12 months, for example. 

The paper is a pre-print, and has not been scrutinized by experts in peer review, or published.

Critical not to misunderstand findings

It is critical that people do not misunderstand these early findings, Hopkins said.  

Hopkins explained that not everyone with antibodies was protected from reinfection, and that it's not known how long immunity lasts for.

"Crucially we believe people may still be able to pass the virus on," she said.

Lawrence Young, virologist and professor of Molecular Oncology at Warwick Medical School said in a statement to the Science Media Centre that the preliminary study showed some of the participants with antibodies still carried a high number of coronavirus particles, called "viral load."

This means that even if people protected themselves, they could continue to spread the virus to others, he said.

It is also not known whether people who catch coronavirus but don't produce antibodies are protected. This study was done in healthcare workers, and there are published surveys in the UK that have shown healthcare workers have higher levels of antibodies than the general public.

The study also took place before the coronavirus variant found in the UK, B.1.1.7, was identified. Some reports suggest people that have been infected with the original coronavirus variant can be re-infected with another. 

"It will be important to determine whether previous infection with the old virus variant is able to offer protection from reinfection with the new virus variant," Young said.

The study is ongoing, and will continue to follow up the health workers for 12 months to work out how long protection lasts, whether vaccines work, and whether people with immunity can pass on the virus.

"These data reinforce the message that, for the time being, everyone should consider themselves to be a potential source of infection for others and should behave accordingly," said Eleanor Riley, professor of Immunology and Infectious Disease at the University of Edinburgh