I wouldn't say "a lot of people". See https://nap.nationalacademies.org/resource/27746/interactive...: only a few conditions, such as Myocarditis, are linked to the mRNA vaccines. I'd be way better off taking even the dodgiest vaccine (Oxford–AstraZeneca, which is no longer in production) than no vaccine, if exposed to actual COVID-19: the reduction in COVID-19 severity would be well worth it in terms of health outcomes (let alone the herd immunity consequences).