Eurosurveillance - Volume 29, Issue 2, 11 January 2024

Women are overrepresented among individuals with post-acute sequelae of SARS-CoV-2 infection (PASC). Biological (sex) as well as sociocultural (gender) differences between women and men might account for this imbalance, yet their impact on PASC is unknown.

We assessed the impact of sex and gender on PASC in a Swiss population.

Our multicentre prospective cohort study included 2,856 (46% women, mean age 44.2 ± 16.8 years) outpatients and hospitalised patients with PCR-confirmed SARS-CoV-2 infection.

Among those who remained outpatients during their first infection, women reported persisting symptoms more often than men (40.5% vs 25.5% of men; p < 0.001). This sex difference was absent in hospitalised patients. In a crude analysis, both female biological sex (RR = 1.59; 95% CI: 1.41–1.79; p < 0.001) and a score summarising gendered sociocultural variables (RR = 1.05; 95% CI: 1.03–1.07; p < 0.001) were significantly associated with PASC. Following multivariable adjustment, biological female sex (RR = 0.96; 95% CI: 0.74–1.25; p = 0.763) was outperformed by feminine gender-related factors such as a higher stress level (RR = 1.04; 95% CI: 1.01–1.06; p = 0.003), lower education (RR = 1.16; 95% CI: 1.03–1.30; p = 0.011), being female and living alone (RR = 1.91; 95% CI: 1.29–2.83; p = 0.001) or being male and earning the highest income in the household (RR = 0.76; 95% CI: 0.60–0.97; p = 0.030).

Specific sociocultural parameters that differ in prevalence between women and men, or imply a unique risk for women, are predictors of PASC and may explain, at least in part, the higher incidence of PASC in women. Once patients are hospitalised during acute infection, sex differences in PASC are no longer evident.

In Sweden, information on seroprevalence of tick-borne encephalitis virus (TBEV) in the population, including vaccination coverage and infection, is scattered. This is largely due to the absence of a national tick-borne encephalitis (TBE) vaccination registry, scarcity of previous serological studies and use of serological methods not distinguishing between antibodies induced by vaccination and infection. Furthermore, the number of notified TBE cases in Sweden has continued to increase in recent years despite increased vaccination.

The aim was to estimate the TBEV seroprevalence in Sweden.

In 2018 and 2019, 2,700 serum samples from blood donors in nine Swedish regions were analysed using a serological method that can distinguish antibodies induced by vaccination from antibodies elicited by infection. The regions were chosen to reflect differences in notified TBE incidence.

The overall seroprevalence varied from 9.7% (95% confidence interval (CI): 6.6–13.6%) to 64.0% (95% CI: 58.3–69.4%) between regions. The proportion of vaccinated individuals ranged from 8.7% (95% CI: 5.8–12.6) to 57.0% (95% CI: 51.2–62.6) and of infected from 1.0% (95% CI: 0.2–3.0) to 7.0% (95% CI: 4.5–10.7). Thus, more than 160,000 and 1,600,000 individuals could have been infected by TBEV and vaccinated against TBE, respectively. The mean manifestation index was 3.1%.

A difference was observed between low- and high-incidence TBE regions, on the overall TBEV seroprevalence and when separated into vaccinated and infected individuals. The estimated incidence and manifestation index argue that a large proportion of TBEV infections are not diagnosed.