Why men are the main COVID-19 transmitters: Despite no observed differences in viral load in nasopharyngeal samples, adult males showed a significantly higher viral load in saliva samples than adult women; plus men have higher aerosol emissions

Men are the main COVID-19 transmitters: behavior or biology? Monize V. R. Silva, Mateus V. de Castro, Maria Rita Passos-Bueno, Paulo A. Otto, Michel S. Naslavsky & Mayana Zatz. Discover Mental Health volume 2, Article number: 1, 2022. Jan 24 2022. https://link.springer.com/article/10.1007/s44192-022-00004-3

Abstract

Background: COVID-19 has affected millions of people worldwide. Clinical manifestations range from severe cases with lethal outcome to mild or asymptomatic cases. Although the proportion of infected individuals does not differ between sexes, men are more susceptible to severe COVID-19, with a higher risk of death than women. Also, men are pointed out as more lax regarding protective measures, mask wearing and vaccination. Thus, we questioned whether sex-bias may be explained by biological pathways and/or behavioral aspects or both.

Methods: Between July 2020 and July 2021, we performed an epidemiological survey including 1744 unvaccinated adult Brazilian couples, with there was at least one infected symptomatic member, who were living together during the COVID-19 infection without protective measures. Presence or absence of infection was confirmed by RT-PCR and/or serology results. Couples were divided into two groups: (1) both partners were infected (concordant couples) and (2) one partner was infected and the spouse remained asymptomatic despite the close contact with the COVID-19 symptomatic partner (discordant couples). Statistical analysis of the collected data was performed aiming to verify a differential transmission potential between genders in couples keeping contact without protective measures.

Results: The combination of our collected data showed that the man is the first (or the only) affected member in most cases when compared to women and that this difference may be explained by biological and behavioral factors.

Conclusions: The present study confirmed the existence of gender differences not only for susceptibility to infection and resistance to COVID-19 but also in its transmission rate.

Discussion

All the results obtained in the present study strongly suggest that males are not only more susceptible to COVID-19 severity, as shown in worldwide epidemiological surveys, but they are also more likely to transmit the virus to their partners when compared to females in the household transmission context. The epidemiological findings in the present survey are consistent with the results of other published studies involving couples where one of the partners was infected by their spouses [40, 41]. Female individuals aged between 17 and 65 years were also frequently found to be secondary cases [41].

Aiming to analyze a more homogeneous cohort and since age is an important predictor of severity and risk of death by COVID-19, we focused our survey on couples of comparable ages and economic status and therefore similar access to health care. It is also important to note that the survey was performed before the vaccination was started.

One of the possible current biological hypotheses for such gender variable transmission rate is a differential viral load in saliva, which has been explored as an important clinical measure of disease severity due to its positive association with many COVID-19 inflammatory markers [42]. These factors, together with the higher adoption of hygiene and protective measures among females, may justify the lower transmission rates in this group.

Interestingly, in a recent study of our group [43] it was observed that, although there were no observed gender differences in viral load in nasopharyngeal samples, adult males showed a significantly higher viral load in saliva samples (verified by RT-LAMP viral testing) than adult women.

These observations, together with the evidence of higher aerosol emission by men which makes them more likely to be “superspreaders” than women, support the hypothesis that male individuals are more efficient virus transmitters than females, which is related to biological and behavioral aspects.

This study has some limitations regarding the relatively modest number of couples included in the present cohort when compared with other epidemiological surveys of in-house transmission [40, 41]. Additionally, the couples who responded the questionnaire are on average younger than the mean age of the population since, in Brazil, younger people have more access and familiarity with internet than older adults [44]. Nevertheless, our study brings new knowledge to the field of public health regarding SARS-CoV-2 transmission dynamics.

In short, the present study confirmed the existence of gender differences not only for susceptibility to infection and resistance to COVID-19 but also in the transmission rate.