有効性
The prioritization of U.S. health care personnel for 
        early receipt of messenger RNA (mRNA) vaccines against severe acute respiratory 
        syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus 
        disease 2019 (Covid-19), allowed for the evaluation of the effectiveness 
        of these new vaccines in a real-world setting.[NEJM]
      
※ efficacy VS effectiveness 「理想環境での効果(efficacy),実際社会での効果(effectiveness)」の違い