Plausible. See data presented in this article: https://dailyexpose.uk/2021/10/31/100-percent-of-covid-19-vaccine-deaths-caused-by-just-5-percent-of-the-batches-produced/

TLDR: 5% of the lots of both Pfizer and Moderna mRNA vaccines were correlated with a large majority of claims of serious adverse effects in the VAERS database. These lots are identified by number specifically in the article as well as the count of SAEs they are associated with. Most of the vaccines are safe, but some are straight up poison.