Prevalence of anti-SARS-CoV-2 antibodies in the general population in Belgium: First results of the SalivaHIS study

Key findings

In the beginning of July 2021 78.1% of the community dwelling population aged 18 years and above had developed anti-SARS-CoV-2 antibodies. This percentage was 98.9% among fully vaccinated people (since at least 2 weeks before being tested) and 28.9% among not vaccinated people.

A higher prevalence of anti-SARS-CoV-2 antibodies is found in woman than in men. This is in line with literature findings indicating that women showed a higher immune response to COVID-19 vaccination.

People with a higher education are more likely to have anti-SARS-CoV-2 antibodies than people with a low education, but this difference is due to a higher vaccination rate among the highest educated.

Vaccinated people with at least one chronic disease are less likely to have anti-SARS-CoV-2 antibodies than vaccinated people without chronic disease. This difference is not explained by socioeconomic differences in the prevalence of chronic diseases. Further research is needed to explore if this difference could be related to a lower immune response of people with certain chronic diseases.

Vaccinated people who were also vaccinated against influenza in 2020-2021 are more likely to have anti-SARS-CoV-2 antibodies than those who did not receive a flu vaccine. A hypothesis is that a flu vaccination in the past vaccination season boosts the immune response to vaccination against SARS-CoV-2.

People vaccinated with a nucleic acid vaccine (Pfizer, Moderna) are more likely to have anti‑SARS‑CoV‑2 antibodies than people vaccinated with a vector-borne vaccine (AstraZeneca, Johnson&Johnson).

In the not vaccinated population, people with a blood type O are less likely to have anti-SARS-CoV‑2 antibodies than people with a blood type A, B or AB. Differences in immune response against the SARS-CoV-2 virus in function of the blood type have been described before, but need further investigation.