The SIREN study from Public Health England’s (PHE) was performed among roughly 20,000 health care professionals and it found that only 44 participants of 6,614 who had COVID-19 antibodies upon recruitment experienced “possible” reinfection — representing an 83% less chance of infection compared to those without antibodies. The study was conducted between June 18 and Nov. 24.
Antibody infection lasted for about five months, on average, from when participants were first infected, SIREN found.
“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,” SIREN study lead and PHE Senior Medical Advisor Susan Hopkins said in a Wednesday statement.
Only two participants experienced “probable” reinfections among the 6,614 participants with COVID-19 antibodies, representing a less-than 1% “probable” repeat infection, SIREN found. Cases were identified as “possible” or “probable” based on “the amount of confirmatory evidence available.”
Hopkins added that people who have already contracted COVID-19 can “be reassured it is highly unlikely” they will “develop severe infections,” but reinfections can still transmit the virus to others.
Only about 30% of participants with antibodies who were reinfected reported symptoms compared to about 78% of those who were infected with the virus for the first time, Hopkins explained during a press release, according to Nature.com.
Still, these results will not ring true for every person infected with COVID-19. One study published in August, for example, shows an example of a Nevada man who experienced severe COVID-19 symptoms after being reinfected with the virus.
Nevada researchers found that a person’s initial exposure to COVID-19 “may not result in a level of immunity that is 100% protective for all individuals.” Researchers also noted in the introduction that with other forms of coronavirus, immunity can be lost within one to three years.
“Now more than ever it is vital we all stay at home to protect our health service and save lives,” Hopkins said in her Wednesday statement.
SIREN researchers will continue to study participants over the course of the next year to see how long COVID-19 immunity lasts among people who have previously been infected with the virus.