A recent study conducted by Sciensano public health institute shows, that, the protection against Covid-19 infection offered by the vaccines wears off rapidly, especially against symptomatic infection with the Omicron variant. Protection against hospitalisation remains stable.
The researchers analysed test results, vaccination status and hospital admissions of 1.5 million Belgian residents between July 2021 and April 2022 – when Belgium dealt with the Delta and Omicron variants.
As per the Sciensano study concluded, “The Covid-19 vaccines used in the Belgian vaccination campaign provide good protection against hospitalisation for Covid-19 infection with the Omicron variant, and lower protection against symptomatic infectio. “Although protection decreases several months after vaccination, protection against hospitalisation increases to 87% after booster vaccination.”
Data from 1,433,135 people were analysed to calculate the protection rate against symptomatic infection (falling slightly ill as a result of a Covid infection), and data from 662,220 people to calculate the rate against hospitalisation.
Those who received the first two doses – the so-called primary or basic vaccination – were initially 81% more protected against symptomatic Delta infection than unvaccinated people. After 100 to 150 days (three to five months), this percentage dropped to 56%. After a booster dose, it climbed back to 84%.
It was not possible to ascertain how long the protection from the booster shot lasted against Delta because the extra doses were only administered when the variant had already almost disappeared in Belgium.
The results are even more striking for protection against the Omicron variant: the initial protection against symptomatic infection after the first two shots was just 37%. This was halved after three to five months.
At the same time, Sciensano researcher Joris van Loenhout said, “the booster shot surpasses the initial protection (52%) but appears to wear off after a few months (25%). “This has to do with the characteristics of Omicron. It escapes the human body’s immune system more easily than, for example, a Delta or Alpha variant.”
As the vaccine was designed for the first variant of the virus, it is “not surprising” that its efficacy against Omicron is fairly low and declines rapidly. “Still, the booster does increase it, especially if we look at protection against hospitalisation. We see that in other studies as well.”