与接种日期有关，超过五个月，对delta效果差。有人分析日本这一波迅速消退的主因是积极的疫苗推广；以色列也因普打加强针使疫情消退

五个月的出处

https://www.eurekalert.org/news-releases/933198

The results show that, compared with individuals who received only two doses five months prior, individuals who received three doses of the vaccine (7 days or more after the third dose) had 93% lower risk of COVID-19-related hospitalization, 92% lower risk of severe COVID-19 disease, and 81% lower risk of COVID-19-related death. Vaccine effectiveness was found to be similar for different sexes, age groups (ages 40-69 and 70+) and number of comorbidities. 

（最神奇的，是下面这一段）

The study also included a population-level analysis which found that infection rates began to drop for each age group 7-10 days after that age group became eligible for the third dose.

 

 

疫苗的群体效果

https://www.news-medical.net/news/20211101/The-effect-of-mass-vaccination-on-COVID-19-mortality-in-Israel.aspx

 

加强针的效果

https://www.timesofisrael.com/israeli-study-covid-booster-shots-92-effective-at-preventing-serious-illness/