Immorality is present when you perform an act with full knowledge of its immorality and with full freedom. In this case, I assume that those who asked this question did not have full knowledge of the immorality involved in these vaccinations, and were influenced by the highest authority in the Church, the Pope.
Therefore, in such cases, their freedom and responsibility were likely diminished. As a result, it was probably not a grave sin for those who received these vaccinations in the past. However, now that you are recognizing and understanding the morality of the issue, from now on, I think you cannot receive any further tainted vaccinations, knowing the matter.