一项基于美国的调查显示，疫苗对新冠肺炎的预防相当有效

https://www.msn.com/en-us/health/medical/breakthrough-covid-cases-rare-among-fully-vaccinated-study/ar-BB1eVxpp?ocid=msedgntp

Researchers examined data from employee health records of more than 36,600 health care workers in California and found that ?less than 1% tested positive for COVID-19 after being fully vaccinated -- meaning both doses plus two weeks for the immunity to build -- with the Pfizer or Moderna vaccines.

Not a single vaccinated health care worker who contracted COVID-19 was hospitalized or died and those who did get sick appeared to have milder symptoms than the unvaccinated, according to the researchers.