The Zurich Coronavirus Cohort Study investigated the extent to which the various SARS-CoV-2 variants reduce the risk of Long COVID and whether vaccination has an effect on the development of Long COVID. The study consisted of 1’350 individuals from two population-based studies, of which 1’045 were from the Zurich Coronavirus Cohort Study and 305 were from the fifth test phase of Corona Immunitas. The findings have now been published in the form of a preprint.
Vaccination has a positive effect
During the study, a total of 25.3% of all those who had been infected with the Wildtype developed Long COVID six months after the infection. They were all unvaccinated since at the time the vaccine was not available. With the Delta infections, the total percentage of those who developed Long COVID was 17.2%, and with Omicron infections it was 13.1%. Taking only unvaccinated people into account, 21.6% developed Long COVID after a Delta infection and 21.9% after an Omicron infection. These figures are comparable with those for the Wildtype. Considering the vaccinated people (at least one vaccination dose prior to infection) on the other hand, “only” 14.8% or 11.1% showed Long COVID symptoms.
Risk of Long Covid six months after infection, in percentages. Figure on the left: 25% have Long COVID after a Wildtype infection. Figure in the middle: 13% have Long COVID after an Omicron infection. Figure on the right: 13% have Long COVID after any Coronavirus infection, after vaccination. (Image: Zurich Coronavirus Cohort Study)
Long COVID reduced but not eliminated
The analysis thus suggests that the risk of long COVID is reduced, particularly in vaccinated individuals who become infected with the omicron variant. The analysis therefore suggests that the risk of Long COVID is reduced, particularly in vaccinated people who got infected with the Omicron variant. Compared to unvaccinated people infected with the Wildtype, the risk of Long COVID following infection with the Delta or Omicron variant is reduced by 45% or 58% respectively. This corresponds to an absolute risk reduction for those infected with the Omicron variant of around 4 in 100 compared to vaccinated people infected with the Delta variant, and 10 in 100 compared to unvaccinated people infected with the Wildtype.
The severity of Long COVID symptoms (the severity has been defined here based on the number of symptoms that occur) following an Omicron infection in a vaccinated person was also lower than with other variants. Nevertheless, it is important to note that there are also people who suffer from serious long-term effects even after Omicron infections.
Long-term effects can still occur despite the reduced risk, and even severe cases are possible.
Important foundations for future vaccination strategies
The study also investigated the impact of vaccination on the long-term effects of COVID-19, and showed that vaccination significantly reduced the risk of Long COVID following an Omicron infection. No difference was detected in connection with the number of vaccination doses (1, 2 or 3). The time between vaccination and infection also had no relevant influence during the study.
Long COVID is not completely prevented by either the vaccination or by new variants. Nevertheless, vaccination had a greater impact in terms of the reduction of Long COVID compared to the new virus variants. These findings are of great importance for future vaccination strategies, the further development of the vaccine and the planning of public-health measures, as well as for individual decisions regarding booster vaccinations.