How effective is vaccination-induced protection against hospital admission? And is vaccine effectiveness different in people with certain underlying health conditions? This is being investigated by UMC Utrecht in cooperation with RIVM in the VECTOR study. 

Why this study?

Vaccination does not offer 100% protection against COVID-19, but people who are vaccinated and still get COVID-19 generally have a lower risk of a severe course of the disease, and therefore have a lower risk of being admitted to hospital due to COVID-19. 
The extent to which vaccines offer protection against infection or hospital or ICU admission is called vaccine effectiveness. Various methods are used to research and monitor vaccine effectiveness. The VECTOR study looks at the protection offered by vaccination in preventing hospital admission due to COVID-19. In addition, it collects information on underlying health conditions in people who are admitted to hospital with a suspected case of COVID-19. As a result, it is also possible to look at vaccine effectiveness in specific risk groups. The study also examines how long protection lasts in different risk groups. 

Who are the patients whose data is collected in this study?

The first part of the VECTOR study took place from March to July 2021, when the alpha variant of the coronavirus was the dominant strain in the Netherlands. Data from 700 patients admitted to hospital with suspected COVID-19 in that period was collected by 6 different hospitals throughout the Netherlands. The data was collected and stored in such a way that the researchers at UMCU and RIVM cannot identify the individuals involved. We are now working on part 2 of the VECTOR study. In this phase, data will be collected from 700 patients who were admitted in the period from October to December 2021. 

What are the research results?

From 1 March to 5 July 2021, 375 COVID-19 patients and 255 patients without COVID-19 were included in the study. Of the 379 COVID-19 patients, 334 were not vaccinated, 40 were partially vaccinated and 5 were fully vaccinated. Of the 255 patients without COVID-19, 145 were not vaccinated, 70 were partially vaccinated and 40 were fully vaccinated. Vaccine effectiveness against COVID-19 related hospital admissions was 93% for full vaccination and 70% for partial vaccination. These calculations took into account the patients’ age, gender and whether they had any underlying health conditions.

All fully vaccinated patients and 39 out of 40 partly vaccinated patients had an underlying health condition. Many of the unvaccinated patients also had underlying health conditions. This was not the case for 14% of the unvaccinated patients. There were no ICU admissions among fully vaccinated COVID-19 patients. 19% of the unvaccinated patients ended up in the ICU.