The question of whether COVID-19 vaccination also reduces viral transmission has to be re-examined with each new coronavirus variant.
When the vaccine was approved at the end of 2020, the level of protection against transmission was not yet known. It was only investigated in subsequent studies. The results were taken into account in the formulation of the vaccination recommendations.
The FOPH explicitly stated the following at a press conference on 19 December 2020: “Even vaccinated individuals will still need to adhere to the protective measures. Vaccination protects people from getting sick, but we still don’t know if it also protects against transmission. We don’t know if vaccinated individuals can also transmit the virus. We will learn more about that over the course of the next few weeks and months.”
The variants initially in circulation (the original and alpha variants) that dominated infection events until about mid-2021 have been observed in studies to show evidence of a reduction in viral spread after COVID-19 vaccination. Knowledge of protection against transmission has changed as a function of the variants in circulation. While there was evidence that vaccination against the first variants could also partially help against transmission, the situation began to change with the emergence of the delta variant in mid-2021. However, the statement that vaccination can help reduce transmission of the virus to other people was still correct, and was based on the latest available data and assessments by international expert panels.
The EKIF and FOPH assume that the booster vaccination does not provide any relevant protection against viral transmission in the case of the omicron variant, dominant since the end of 2021, and its subvariants. However, all booster vaccinations still increase protection against severe cases of illness, which is the main goal of the COVID-19 vaccination strategy.
Findings from clinical trials, other available evidence and assessment of the current epidemiological situation continuously inform revisions to the vaccination recommendations.