evidence: In any new large vaccine rollout, some people will experience a serious medical problem in the period after the new vaccine is given, and wonder "was it from the vaccine?". [...] Strong vaccine safety systems are designed to identify and investigate potential new health issues related to a vaccine. [...] A recent Danish study, yet to be peer-reviewed, for example, showed fewer new health problems four months after Omicron infection in people given a booster compared to those given only two doses of COVID-19 vaccine.