While vaccinations or a previous coronavirus infection provide less effective protection against the Omicron variant when compared with Delta, a booster does ensure renewed protection, according to new research by public health institute RIVM.

The risk of picking up a Delta infection was 76% lower after a completed basic series of Covid-19 vaccinations and 78% lower after an infection, compared to a person who was unvaccinated and had not previously had an infection, the RIVM said.

However, both vaccination and previous infection were much less effective against the Omicron variant, at 33% and 25% respectively. After a booster vaccination, protection against infection with Delta rose to 93% and to 68% for Omicron, the RIVM research shows.

The research was based on 500,000 test samples from regional health board testing centres and were carried out between November 22 and January 19. At the start of the test period, the percentage of Omicron tests was 0%, but this had risen to 95% by the end.

Some 60% of Dutch adults have had a booster dose, but the national health council does not recommend boosters for teenagers.

‘International research shows that protection offered by vaccination is more effective in preventing hospital admission (severe infection) than mild infection,’ the RIVM said. ‘A booster vaccination intensifies that protection which means that… after basic vaccination and booster vaccination, you have a much lower risk of becoming seriously ill.’

Pfizer/Biontech and Moderna are currently developing vaccines which specifically target the Omicron variant.