SAO PAULO — A study by USP (University of São Paulo) followed 1,744 couples for a year and found that, in 63.5% of those in whom both husband and wife were infected with Covid-19, it was the man who took the virus to inside home.
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It was already known that women are in an unequal position in the risk of transmission because men are, on average, more careless with sanitary measures. The new study, however, indicates that there is a biological factor that makes them more likely to transmit Sars-CoV-2, not just contract it.
The difference observed in the study was not small. Among “agreeing” (double-infected) couples, women were only 36.5%, suggesting that men are 1.7 times more infectious than women.
— Men transmit more and, therefore, they should even take more care, both with the vaccine and the mask, but that is not what we see happening — says geneticist Mayana Zatz, leader of the group that carried out the study at the Institute of Biomedical Sciences at USP. The work was coordinated by researchers Monize Silva and Mateus de Castro.
Zatz says the data was extracted as a secondary result of the sampling of volunteers that his research group follows for genetic studies. (The scientist seeks to identify hereditary factors in the propensity to contract Covid-19.)
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Curiosity about the gender disparity arose when the scientists collected saliva and nasal cavity samples for the work. They initially identified that viral load was similar for infected men and women in nasopharyngeal specimens. In saliva, however, infected men had ten times more virus, which has already been reported in another study of the group.
– As we know that saliva is the preferred route of transmission, we decided to investigate, and went back to analyzing the questionnaires that the volunteers had answered – says the researcher.
Investigating couples was a more reliable way of assessing whether men are biologically more contagious than women, because couples typically don’t wear a face mask when alone indoors.
According to Zatz, despite the study having found this transmission capacity greater by men, the reasons still need to be further investigated.
– It may be that there is a hormonal factor, because this difference appeared in the group up to 48 years of age, but not in the older ones – says the scientist. “On the other hand, men have a larger rib cage, so they might also produce more virus in their saliva.
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The study by Zatz’ group has not yet been published in a scientific journal with independent review. The work is currently available in a “pre-print” (preliminary study) version on the MedrXiv portal.