What is vaccination coverage and how is it calculated?
A growing number of people have had their first vaccine dose or are now fully vaccinated. ‘Vaccination coverage’ is the proportion of people who are vaccinated. The method used by the National Institute for Public Health and the Environment (RIVM) to calculate vaccination coverage by age group and municipality differs from that used by the European Centre for Disease Prevention and Control (ECDC) to calculate total vaccination coverage. RIVM and ECDC therefore arrive at different figures, as we explain below.
RIVM keeps a record of how many vaccine doses have been given. So we know how many people in the Netherlands have received their first and second doses. On the coronavirus dashboard, we show the number of people who are partially and fully vaccinated.
By September 2021, we also want to provide vaccination coverage data by age group and municipality on the dashboard. RIVM and ECDC have this data. RIVM uses different data to calculate vaccination coverage by age group and municipality than it uses for its estimate of total vaccination coverage in the Netherlands, which is reported to ECDC.
ECDC: number of vaccinated adults in the Netherlands
ECDC provides data on vaccination coverage among all adults in the Netherlands, based on figures passed on by RIVM. The ECDC website shows the number of adults who have received at least one dose and the number of adults who are fully vaccinated.
ECDC receives an estimate from RIVM of the number of doses that have been administered. In the case of the municipal health services (GGDs), this is done on the basis of anonymously recorded vaccinations. Vaccinations administered by general practitioners (GPs) and institutions are only recorded by RIVM with the consent of the person being vaccinated. To get as complete a picture as possible of the number of doses administered by general practitioners and institutions, the number of doses supplied by RIVM is taken into account. The number of doses administered by general practitioners and institutions is estimated on the basis of, among other things, the number of potential doses in each vial and estimated spillage. Adding together the number of recorded GGD vaccinations and the estimated number of doses administered by general practitioners and institutions provides a picture of total vaccination coverage among adults in the Netherlands.
Because this is in part an estimate, actual vaccination coverage may be different. Especially because it is not clear how many doses supplied to general practitioners and institutions remain unused. Nor do the figures on doses administered by general practitioners and institutions show the age of the people vaccinated or the municipality where they live.
RIVM: vaccination coverage by age group and municipality
RIVM keeps a record of how many people have been fully vaccinated or have received their first dose in CIMS, its national registration system. It includes vaccination information passed on by the GGDs, general practitioners and institutions in cases where the person vaccinated has given their consent. RIVM also has a complete set of anonymised data for vaccinations administered by the municipal health service, for which no consent is needed from the person concerned. This anonymised data together with the CIMS data enable RIVM to see the age of people who have been vaccinated and the municipality where they live. This enables RIVM to show vaccination coverage by municipality or age group.
The number of people registered is large enough to provide a clear enough picture of vaccination coverage by age group and municipality. The true rate of vaccination coverage is higher than that recorded in CIMS, because the latter does not include people who did not consent to their vaccination data being recorded in CIMS and who were not vaccinated by the GGD.
Differences in the figures
ECDC’s website stated on 4 August 2021 that at 84.8% of adults in the Netherlands have had at least one dose and that 66% are fully vaccinated. In its weekly report, RIVM does not publish figures on total vaccination coverage, but does give figures by age group and municipality. If you add up RIVM’s figures for each age group, you arrive at a figure of nearly 80% of adults in the Netherlands who have received at least one dose and almost 63% who are fully vaccinated. There are several reasons for the difference between RIVM’s figures and ECDC’s.
Firstly, as mentioned above, someone who has been vaccinated can choose whether or not they are recorded in CIMS, RIVM’s register. Because some people do not give their consent, not all vaccinations are recorded in RIVM’s system. The real vaccination coverage by age group and municipality is therefore higher than recorded. But the people who do not give their consent are included in ECDC’s figures, because the number of doses administered by general practitioners and institutions is estimated on the basis of the vaccines supplied. The rate of vaccination coverage calculated by ECDC is therefore slightly higher.
Secondly, RIVM uses a more recent source of information on how many people live in the Netherlands than ECDC does. The source used by ECDC gives a lower number of inhabitants. ECDC therefore calculates a higher vaccination coverage, since vaccination coverage is a percentage of the total population that is vaccinated.