Besides being more susceptible to contracting severe Covid-19 and to dying from the disease, men are more likely to be infected first and to transmit the SARS-CoV-2 virus faster than women.
This is according to a study by researchers from the University of São Paulo’s Human Genome and Stem Cell Research Center (HUG-CELL), who analysed data from an epidemiological survey involving 1,744 Brazilian couples.
“Our findings corroborate, and are in accord, with discoveries made by our own recent studies, which suggested men transmit the virus more than women,” said Mayana Zatz, a professor at the university’s Institute of Biosciences (IB-USP) and principal investigator for HUG-CELL.
A study published in early August (2021) in the journal Diagnostics analysed the results of a test that detects SARS-CoV-2 in saliva and was developed by researchers at HUG-CELL.
The viral load in men’s saliva was about 10 times higher than in women’s, especially for subjects aged 48 or less.
This difference in viral load was not detected by a nasopharyngeal swab test, according to the study, which was led by IB-USP professor of genetics Maria Rita Passos-Bueno.
“Because the virus is mainly transmitted in saliva droplets, we deduced that this explains why men transmit it more than women,” said Prof Zatz.
In addition to this observation, Prof Zatz had received reports of couples – many of whom were both physicians – where the female partner was infected by SARS-CoV- 2 and manifested mild or moderate symptoms, while the male partner had no symptoms.
Some months later, the male partner was infected after coming into contact with male patients, reinforcing the theory that men transmit the virus more than women.
To test the hypothesis, the HUG-CELL researchers collected data from more than 2,000 couples with an average age of 45 and not then vaccinated against the coronavirus.
At least one partner was diagnosed to have contracted Covid-19 and manifested symptoms.
The data was collected between July 2020 and July 2021 by means of emails and questionnaires.
To rule out behavioural differences – such as men’s greater reluctance to wear a face mask and maintain physical distancing, demonstrated by research conducted during the pandemic – the researchers analysed viral transmission in more than 1,000 couples who cohabited during the period without conjugal distancing or other protective measures.
The couples were divided into a concordant group, in which both partners were infected, and a discordant group, in which one partner remained asymptomatic, despite close contact with the infected partner.
The combined data showed that in both groups, the male was the first or only partner infected in most cases.
“We found that men were infected first much more than women, in concordant, as well as discordant couples.
“A total of 946 men were infected first, compared with 660 women,” said Prof Zatz.
The researchers also analysed genetic material from couples in which only one partner was infected by SARS-CoV-2, although both were exposed to the virus.
This was to understand why some people are naturally resistant to infection.
Preliminary results of this study suggest that genomic variants more frequently found in susceptible partners led to the production of molecules that inhibit activation of immune defence cells known as natural killer cells.
Both the studies, funded by the public São Paulo Research Foundation (FAPESP), were posted to the preprint platform medRxiv, which hosts research not yet certified by peer review.
The complete findings of the study suggesting that men transmit the SARS-CoV-2 virus more than women, which was conducted in collaboration with São Paulo State University in Botucatu researcher Erick Castelli, will be published shortly in the journal Frontiers in Immunology. – By Elton Alisson/Agência FAPESP