In ‘Viruses’, Leclercq and colleagues present the results from the SalivaHIS study. This project is a  prospective cohort study in which saliva samples and questionnaire data are collected from a random sample of the Belgian adult population. The saliva samples are used to measure the presence of antibodies against SARS-CoV-2, which suggests that a person has previously been infected with COVID-19 or has been vaccinated. Between March and August 2021, a total of 2,767 

individuals participated in the first round of data collection. The results show that the prevalence of anti-SARS-CoV-2 antibodies among the general population in Belgium increased during the study period, a time when the vaccination campaign was ongoing. Related to the prioritisation of the vaccination campaign, vaccinated people were relatively older and included a higher share of women, health care workers, people with at least one chronic disease, and people vaccinated against influenza. 

Among the vaccinated, factors significantly associated with the presence of anti- bodies were: having at least one chronic disease, having received an mRNA-type vaccine (Pfizer-BioNTech or Moderna), and having received an influenza vaccine in 2020–2021. Among the unvaccinated, having a non-O blood type and having one or more positive COVID-19 tests were significantly associated. 

The full article is available via: https://www.mdpi.com/1999-4915/14/5/920