The researchers studied the antibodies in 500 staff members at the Hôpitaux Universitaires de Strasbourg (HUS), who had a positive PCR test result and, in most cases, mild symptoms. A first sample was taken 15 days after the onset of symptoms, then at 3-6 months.
“We noticed that even people with mild symptoms can develop neutralising antibodies”, explains the virologist, who points out that different serological tests were used. Two tests targeted the spike protein, the key that enables SARS-CoV-2 to enter our cells. Another targeted the nucleocapsid, a protein that surrounds the nucleus of the virus. And a final one assessed the neutralising power of antibodies, “those that prevent the virus from entering the host cell.”
Are women better protected because of their X chromosome?
The result: “Men over the age of 50 or with a body mass index above 25 have a high level of antibodies 1 month after symptoms. However, their antibody level drops very quickly over time, in contrast with women, in whom it remains more stable. “3 to 6 months after the beginning of the study, the antibody level in 32% of the women remained unchanged, compared with only 8% of the men, which would indicate a longer immunity in women than in men. This is independent of age and body mass.”
How can this be explained? “Generally speaking, with infections, women are known to have a stronger immune response than men, probably due to their extra X chromosome, which carries the majority of the genes involved in the immune response, and to the sex hormones that protect them. It should be noted that this male/female difference has also been reported by a team from the University of Yale, which showed that women have a more robust and more stable anti-SARS-CoV2 T-cell response over time than men.”
The study will continue until July 2021
Another finding of the study was that the percentage of people who tested positive for SARS-CoV-2 went from 99% with the tests targeting the S protein, to 59% with the test that targeted the nucleocapsid. “According to the serological test used, it is possible to underestimate the number of people having contracted Covid-19.”
The study will continue until July 2021. If the male/female difference continues over time, vaccination campaigns could be targeted not only based on age but also on sex.
* Since its launch on 15 April 2020, the Serocov-HUS study has been monitoring the immune response to Covid-19 of 1 500 HUS staff members. 500 had a positive RT-PCR test, 500 had symptoms but a negative PCR test and 500 were chosen randomly. A paper is in the pipeline.