Possibly Russian book in which some humas had their head transformed into metallic balls

There is a sci-fi novel I read in the years before 1989 (before the Romanian revolution against communism; I am from Romania) and I liked very much but I don't remember its name and author.

Because of the political situation in that time, I believe it must have been written by a Russian author but I don't know this for sure.

Sadly, all I remember from the novel is this: there was a plague which affected humans by transforming their heads into "metallic?" balls. I could have been the effect of some alien transmission, but I don't remember much (just the feeling of reading a great book).

Also for the Romanian users here on stackexchange, I think that the cover was yellow and the format was small.

Can anybody help me remember the name / author of the book?