> any adverse effects would have shown

As I understand, the required teratogenicity study in rats with Pfizer is ongoing as of two weeks ago [1]. It’s rather optimistic to claim we’ve seen everything when even animal studies haven’t completed. Vaccine science itself is rapidly developing. Now I don’t think there will be issues with this drug, but surprises may lurk still.

[1]: https://www.gov.uk/government/publications/regulatory-approv...