According to SIREN (Sarscov2 Immunity & REinfection EvaluatioN) study being conducted by Public Health England (PHE), those who were previously infected with COVID-19 are likely to be immune against the disease for several months, although they still could infect others.
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The study was launched last June. Until 24 November 2020, PHE has performed regular antibody and PCR testing on 20,787 healthcare workers, the largest study in the world so far. Of those 6,614 tested positive for COVID-19 antibodies upon recruitment, with 44 potential reinfections (2 ‘probable’ and 42 ‘possible’ reinfections) detected.
None of the 44 potential reinfection cases were PCR-tested during the first wave of the pandemic, but upon recruitment all tested positive for COVID-19 antibodies, which suggests they had the disease before. If all 44 cases were confirmed, it would represent an 83% rate of protection from reinfection. With only the 2 ‘probable’ reinfections confirmed, the rate would be 99%. Currently scientists are working to clarify this range.
According to the preliminary results of the study, antibody immunity lasts for at least 5 months. This means those who got infected during the first wave may not be protected now, although assessment of whether the immunity may last longer is ongoing (participants will be followed for 12 months). At the same time, the immunity does not prevent people from carrying the virus and thus infecting others, the study emphasises.
It is noted that because of the first stage’s time limits, the study currently does not provide any evidence with regard to COVID-19 vaccines, which were rolled out later in 2020; PHE will focus on vaccine responses at a later stage. For the same reasons, the results do not include the analysis of the new variant of the virus, VOC202012/01, but the researchers are now studying its impact on symptomatic and asymptomatic infections in healthcare workers.
Source and image credit: PHE