In addition to the greater susceptibility to presenting severe conditions of Covid-19 and dying from the disease, men are more primarily infected and, consequently, may be the main transmitters of Sars-CoV-2. This is what a study by researchers at the Center for the Study of the Human Genome and Stem Cells suggests, based on an epidemiological survey involving 1,744 Brazilian couples. You work results were published on the medRxiv platform, in an article still without peer review.
“This finding corroborates and is in line with discoveries made in recent studies that we carried out, which already indicated that men can transmit the new coronavirus more”, he tells Agência FAPESP Mayana Zatz, professor at the Institute of Biosciences of University of Sao Paulo and coordinator of the Center for Genome Studies, one of the Research, Innovation and Diffusion Centers financed by FAPESP.
Study published in early August by researchers at the Center in the journal Diagnostics, based on a test for detecting Sars-CoV-2 in saliva developed by the researchers, found that men have a virus load in the fluid about ten times greater than women, particularly up to 48 years of age. This difference in viral load was not detected in tests with nasopharyngeal samples, pointed out the authors of the study, coordinated by the professor Maria Rita Passos-Bueno.
“Since the virus is transmitted mainly by saliva droplets, we deduced that this would explain why men transmit more viruses than women,” says Zatz. In addition to this observation, the researcher began to hear reports from couples – many of them both doctors – in which the woman was infected by the virus and showed mild or moderate symptoms, while the man remained asymptomatic. A few months later, the spouse was also infected after contact with male patients, which reinforced the theory that men transmit more of the new coronavirus.
In order to evaluate the hypothesis, the researchers began to collect, between July 2020 and July 2021, data through e-mails and questionnaires from more than 2,000 couples, with an average of 45 years of age until then not vaccinated against covid-19, in which at least one of the spouses was infected, diagnosed and showed symptoms of the disease.
To eliminate the influence of behavioral biases, such as the fact that men are more reluctant than women to use protective masks and respecting social distance, as proven by studies during the pandemic, the transmission of the virus in more than a thousand couples who lived together during the period of infection without taking protective measures was analyzed.
Couples were divided into concordant groups – in which both partners were infected – or discordant – in which one of the spouses remained asymptomatic, despite close contact with the infected.
The combination of data collected showed that men were the first or the only ones infected in most cases, both among concordant and discordant couples.
“We saw that men were first infected much more than women, in both concordant and discordant couples. In total, 946 men were infected first compared to 660 women,” says Zatz.
The investigation received funding from the Foundation for Research Support of the State of São Paulo (Fapesp) through two other projects.
The researchers also analyzed the genetic material of couples in which only one spouse was infected, although both were exposed, with the aim of understanding why some people are naturally resistant to the infection.
Preliminary results from the study, also published on the medRxiv platform, indicated that more frequent genomic variants in susceptible partners would lead to the production of molecules that inhibit the activation of defense cells known as natural killers or NK. The complete results of the study, carried out in collaboration with Professor Erick Castelli, from Paulista State University (Unesp), Botucatu campus, will soon be published in the magazine Frontiers in Immunology.