SalivaHIS - Study on the prevalence of antibodies against the coronavirus (SARS-CoV-2) in the Belgian population

Last updated on 5-5-2022 by Marinka Vangenck
January 1, 2021
June 30, 2022

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In short

During the current corona crisis, a randomly selected group of the adult population in Belgium receives a saliva test kit to collect a saliva sample from themselves. Sciensano then examines samples to determine the prevalence of antibodies against the coronavirus in the general population. Information on the health status and lifestyle characteristics of participants is also collected via a self-administered questionnaire. 
The results of this study will support Belgian policymakers in the decisions they have to make with respect to the corona crisis, such as the vaccination strategy. In addition, these results will provide useful research data to understand different aspects of the epidemic.

Project summary

The aim of the study is to provide information on the prevalence of people with anti-SARS-CoV-2 antibodies in the general Belgian adult population over time and to study to what extent this prevalence varies in function of health status and lifestyle characteristics (e.g. diseases, mental health, functional status, smoking behavior, BMI, coronavirus-related health,…). This study also investigates the adherence to prevention measures and the variation in the presence of antibodies within the same household. In order to follow up the evolution of the presence of antibodies in time, the study will be repeated after 3 and 6 months. The study will also allow the monitoring of the presence of anti-SARS-CoV-2 antibodies in vaccinated people.
The SARS-CoV-2 seroprevalence is determined in a random sample of the general adult population in Belgium. This includes people who have no contact with health services. The study is therefore complementary to other seroprevalence studies in Belgium which focus on specific groups (blood donors, school children, health care workers, rest home residents).
If the study participants give their consent, Sciensano stores their saliva samples in its biobank, and the data collected in this study can be linked in an encrypted way with data from administrative and clinical databases for further scientific research.

The primary outcome of this study is the seroprevalence status of anti-SARS-CoV-2 antibodies in the general adult population. Secondary outcomes are:

  • the evolution of the presence of anti-SARS-CoV-2 antibodies over time
  • the cumulative incidence of antibody development
  • characteristics of participants with a positive result
  • the proportion of symptomatic seropositive cases
  • follow-up of SARS-CoV-2 seroprevalence in vaccinated persons.

Results

The main findings of the 2nd phase (from September to November 2021):

  • During the period September to November 2021, 92.9% of the adult population in Belgium had antibodies against SARS-CoV-2. The prevalence was 98.0% in fully vaccinated individuals who received the last dose (eventually a booster dose) in the past 3 months, 94.5% in fully vaccinated individuals who received the last dose (eventually a booster dose) longer than 3 months ago, and 30.4% in unvaccinated individuals.
  • The majority of participants who did not have antibodies against the coronavirus in the first phase of the study (the period of April to August 2021) were found to have antibodies in the second phase (87.8%). This is mainly explained by the vaccination campaign in Belgium. Conversely, 3% of the participants who had antibodies in the first phase of the study no longer had antibodies in the second phase of the project
  • In the general population, the risk of not having antibodies to anti-SARS-CoV-2 increases with age
  • In the fully vaccinated population, those who are over 50 and those with at least 1 chronic illness are at greater risk of not having antibodies to anti-SARS-CoV-2. The risk of not having antibodies increases with the time since the last vaccine dose. 

The main findings of the 1st  phase (from April to August 2021): 

  • By early July 2021, 98.9% of vaccinated participants had antibodies. Among the non-vaccinated participants, this was only 28.9%. More antibodies are found in higher educated people than in lower educated people. This is largely due to the higher vaccination coverage among the higher educated.
  • Vaccinated persons are less likely to have antibodies when they have at least one chronic disease.
  • Persons who were vaccinated against the influenza virus produce antibodies against the coronavirus more easily. It is not clear what causes this. It is possible that the flu vaccine strengthens the immune response of the corona vaccine.

Associated Health Topics

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