Anecdotal - but of people I know that had breakthrough cases despite full Pfizer vaccination, half of them had moderate disease. Eg 104+ fever for 7 days. One ended up briefly hospitalized with oxygen. More concerning is the data from Israel showing that even mild breakthrough cases can result in long covid that can last months. That study was small, but showed 20% risk of long covid in breakthrough cases.

âoeIn this placebo-controlled vaccine trial, we found that previous infection with first-wave prototype-like, pre-B.1.351 viruses did not appear to reduce the risk of Covid-19 due to subsequent infection with B.1.351 variants among placebo recipients during the initial 2 months of follow-up. This finding is preliminary and may have public health implications for pandemic modeling, control strategies, and vaccine development and deployment efforts. It is also consistent with the lack of incremental benefit conferred by preexisting immunity in vaccine recipients as evidenced in our trial by consistent levels of efficacy regardless of baseline serostatus for SARS-CoV-2. Although these findings require further confirmation, our observations suggest that vaccination with prototype-sequenced NVX-CoV2373 conferred a degree of cross-protection against an immunologic escape variant.â https://www.nejm.org/doi/full/...

This seems to be a common misconception. The EUA application is essentially the same as the full approval application in terms of the data required. The normal approval process for vaccines does not require long term following of test subjects prior to approval. The reason why is that vaccines are dosed once or twice, and for every vaccine weâ(TM)ve ever made, adverse events tend to show up within the first 1-2 months after vaccination. And this makes sense. Your body is not experiencing chronic exposure to a drug as it would for something like viox. So the main threat is from triggering a faulty immune response that either attacks your own tissue, or enhances disease. The clinical trials of 10s of thousands of people establish a pretty high safety threshold. Even vaccines with rare problems (J&J) are still very safe. The 100 million+ that have been vaccinated after the trials completed are also proving the vaccine to not only be very safe, but also highly effective