People who have previously been infected with coronavirus and who are themselves protected by antibodies could still carry the virus and infect others, according to a study conducted in England.
The study, called “SARS-COV-2 Immunity and Reinfection Evaluation” (SIREN) and conducted between June 18 and November 24, 2020, also found that while reinfection is possible, it appears to be rare, at least for the first five months after becoming sick.
The BMJ and the science journal
Nature, among other publications.
Of the participants in the study who had already fallen ill (around 6,600), only 44 (less than 1%) were reinfected with the virus. In other words, immune response from a first infection reduced the risk of contracting the virus again by 83%.
Of the roughly 14,000 people who had not been previously infected in the study, 318 tested positive for the virus (2.3%).
The researchers do not know how long the protection lasts beyond the timeframe of the study.
Moreover, those who were reinfected did not usually suffer from serious illness. Only about 30% of the people with possible reinfection reported any symptoms, compared to 78% of those who contracted the virus for the first time.
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But, as noted, sometimes those who had recovered and were then reinfected had high viral loads, meaning there was still a high chance that they would transmit the virus to others.
The study was not meant to give insight into the effects of the vaccine. Also, the researchers noted that the goal was not to assess whether symptoms were better or worse during the second infection, and this question requires further evaluation.
The subjects were mostly young, middle-aged females who anyway tend to have less severe symptoms than older people.
This is not the first study published on reinfection. A
separate study that was published in November, also in England, found that people who had the virus are highly unlikely to contract it again for at least six months after the first infection.