隨著時間的推移，接種越早的人對變異毒株抵抗的有效性衰減越多。今年一月份接種的人，根據以色列研究，疫苗有效性已經降到16%。

Over a 4-week period (20 June to 17 July 2021), Pfizer’s general effectiveness decreased as the time before exposure increased: efficacy was 79% for those who received their second dose in April, 69% for March, 44% for February, and 16% for people who were fully-vaccinated back in January.

https://www.google.com/amp/s/www.forbes.com/sites/jvchamary/2021/07/29/pfizer-covid-19-coronavirus-vaccine-effective-delta-variant/amp/