Class action is very limited in Finland - the law that allows this is quite recent, there has been no class action suits yet at all and I'm not sure if it would be even applicable here.
The situation is much the same in Sweden, however the GDPR has an article that specifically allows class actions. It remains to see how it would work out in practice.
In an interview of a lawyer, they said that this article has not been implemented in the Finnish legislation (or at least not properly for a health care case like this - I didn't fully catch it).