The flu shot is not mandatory, nor should it be. Partly becase low effectiveness, partly because it's sensitive to mutations, partly because the risk of complications, while not zero, is relatively low.
Polio vaccine is a bit of an outlier. 3 doses give 99% effectiveness.
MMR 2 doses is 97% effective against measles and 88% against mumps.
The jury is still out on how effective mRNA is against covid delta, studies are all over the place, 42% to 96% for Pfizer. A lot of people are concerned that mutations evading the vaccine are likely to occur, including Pfizer CEO.
https://www.cdc.gov/vaccines/vpd/polio/hcp/effectiveness-dur...
https://www.cdc.gov/vaccines/vpd/mmr/public/index.html
https://www.healthline.com/health-news/heres-how-well-covid-...