Vaccination offers more than 80% protection against an infection with the coronavirus SARS-CoV-2 among people under 70 years old who are tested due to symptoms. Among people over 70 who get tested due to symptoms, vaccine-induced protection against infection is 73%. This is evident from new analyses by RIVM National Institute for Public Health and the Environment regarding the period from 4 July to 2 December 2021. During this period, the Delta variant was the dominant strain in the Netherlands.
RIVM National Institute for Public Health and the Environment is researching the protection provided by the COVID-19 vaccines in various ways. Previous updates covered such topics as the risk of hospital and ICU admission and the risk of coronavirus transmission. For the first time, RIVM is now publishing updates on vaccine effectiveness in preventing a SARS-CoV-2 infection based on time elapsed since vaccination, including specification based on which vaccine was administered. Researchers looked at effectiveness in people who were tested due to relevant symptoms and people who were tested in the context of source and contact tracing. The definition of infection used here is a SARS-CoV-2 infection detected on the basis of a positive test result for COVID-19 from a PCR test or antigen test. The effects of booster vaccination have not yet been included in this study.
Effectiveness against infection lower for people over 70
Among people tested due to symptoms, vaccine effectiveness over the entire research period was 85% for people aged 12-29 years, 83% for people aged 30-49 years, and 82% for people aged 50-69 years. Vaccine effectiveness in preventing infection is lowest in the age groups above 70 years old, only reaching 73%.
Dependent on type of vaccine and time since last vaccination
Looking at decreasing effectiveness over time since vaccination, RIVM has observed a difference between mRNA vaccines (Pfizer/BioNTech and Moderna) and vector vaccines (Janssen and AstraZeneca). mRNA vaccines achieve very high effectiveness two weeks after the second vaccination, ranging between 75% and 90%. Over the course of six months, this gradually decreases to 70-80%. After six months, effectiveness seems to stabilise at that point in people under 70 years of age. For people over 70, mRNA vaccines are not quite as effective shortly after vaccination (around 75%) compared to younger people, and effectiveness also decreases more significantly, dropping to around 50%.
The vector vaccines show an increase in effectiveness – depending on age – in the first few months after vaccination. For example, among people aged 50-69 years who were tested due to symptoms, the Janssen vaccine was about 50% effective in preventing infection after four weeks, rising to about 75% after three months.
Dependent on close contact with person who tested positive
Vaccine effectiveness was assessed separately for people who were tested in the context of source and contact tracing, and had therefore definitely been in close contact with someone who had tested positive for COVID-19. RIVM observed lower vaccine effectiveness in these people (a difference of about 10-20%) than in people who were tested due to symptoms. Previous research already showed that the vaccines offer less protection against infection in the event of high-level exposure to the coronavirus SARS-CoV-2.