The German pharmaceutical company Biontech and its American partner Pfizer want to add a third dose to the ongoing clinical studies on the corona vaccine for smaller children between the ages of six months and four years.
A third vaccine dose will now be investigated, which will be administered two months after the second at the earliest, the companies announced on Friday.
This means that the results that have been expected for this year or the beginning of next year are likely to be delayed; companies are now assuming the "first half of 2022".
The decision was made because initial data showed that children between the ages of two and five years did not respond as well to the vaccination as adolescents and adults aged 16 and over and as children between 6 and 24 months.
Safety concerns were not found, it said.
According to the company, around 4,500 children between six months and eleven years from several countries take part in the study.
The vaccine has now been approved for children aged five and over in the United States and the EU, among others.
Biontech and Pfizer now also want to investigate a third dose of vaccine for children between the ages of five and twelve.