This evidence synthesis has been compiled by members of the CITF Secretariat and does not necessarily represent the views of all CITF members.

By Mercedes Yanes Lanes

SpaceX does not just send red convertibles into space, they are also now a cohort for SARS-CoV-2 immunity. This study, published in Nature Communications, was carried out  in a cohort  of Space Exploration Technologies Corp. employees and specifically followed the subset of participants who had a positive serology test with no history of vaccination.

The initial cohort enrolled 4,300 volunteers, of which 120 where positive for antibodies against a portion of the SARS-CoV-2 virus called the receptor binding domain (RBD)The region of the SARS-CoV-2 spike protein that binds to the cellular receptor to trigger viral entry.. These participants included COVID-19 symptomatic and asymptomatic individuals, with varying antibody levels. Notably, higher antibody levels were found in more symptomatic individuals, but findings were heterogeneous over time. Some participants who had high antibody levels at the first measurement showed a decline by the second measurement, whereas other participants with low initial antibody levels seemed to show an increase over time. It is likely that these, taken together, show the natural progression of an immune response, with a rise, peak and waning profile.

To determine if the presence of antibodies protects against COVID-19, the samples from 120 participants were split into two groups based on their antibody levels, and the antibodies found in each sample were put to the test to see how effectively they could eliminate SARS-CoV-2. Samples with higher levels of anti- RBD antibodies did better at eliminating the virus. However, while samples with low levels of anti-RBD produced antibodies targeting other parts of the virus, these did not seem to compensate for anti-RBD function.

Data presented in this study points to a threshold that might exist in the level of antibodies produced by a natural infection, above which an individual is likely protected against reinfection. This threshold could serve as a surveillance mechanism and as a way to prioritize vaccination in those who are most vulnerable.

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