In addition to the greater susceptibility to presenting severe conditions of COVID-19 and dying from the disease, men are more firstly infected and, consequently, they can be the main transmitters of SARS-CoV-2. This is what a study by researchers from the Center for Human Genome and Stem Cell Studies (HGH-CEL) – one of the Research, Innovation and Dissemination Centers (CEPIDs) financed by FAPESP –, based on an epidemiological survey involving 1,744 Brazilian couples.
The results of the work were disclosed on the platform medRxiv, in an article still without peer review.
“This finding corroborates and is in line with findings made in recent studies that we carried out, which already indicated that men can transmit more of the new coronavirus”, he tells the FAPESP Agency Mayana Zatz, professor at the Institute of Biosciences of the University of São Paulo (IB-USP) and coordinator of the CEGH-CEL.
A study published in early August by researchers from the Center in the journal Diagnostics, based on a test for detecting SARS-CoV-2 in saliva developed at the HGH-CEL, 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 with the new SARS-CoV-2 and presented 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 assess the hypothesis, the HGH-CEL 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 age of 45 years 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 wear protective masks and respect social distancing, as demonstrated by studies during the pandemic, the transmission of the virus in more than 1,000 couples who lived together during the period of infection without taking protective measures.
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 FAPESP through two other projects: 14/50931-3 and 20/09702-1.
The researchers also analyzed the genetic material of couples in which only one spouse was infected with SARS-CoV-2, although both were exposed, with the aim of understanding why some people are naturally resistant to the infection.
Preliminary results of the study, too. published on the platform medRxiv, 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 (Read more at: agency.fapesp.br/35752/).
The complete results of the study, done in collaboration with the professor Erick Castelli, from Universidade Estadual Paulista (Unesp), Botucatu campus, will be published soon in the magazine Frontiers in Immunology.
The article Men are the main COVID-19 transmitters: lessons from couples (DOI: 10.1101/2021.08.18.21262187), by Monize VR Silva, Mateus V. de Castro, Maria Rita Passos-Bueno, Paulo A. Otto, Michel S. Naslavsky and Mayana Zatz, can be read on the platform medRxiv in: www.medrxiv.org/content/10.1101/2021.08.18.21262187v1.