Waning Immunity after the BNT162b2 Vaccine in Israel

Background:In December 2020,Israel began a mass vaccination campaign against coronavirus disease 2019(Covid-19)by administering the BNT162b2 vaccine,which led to a sharp curtailing of the outbreak.After a period with almost no cases of severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)infection,a resurgent Covid-19 outbreak began in mid-June 2021.Possible reasons for the resurgence were reduced vaccine effectiveness against the delta(B.1.617.2)variant and waning immunity.The extent of waning immunity of the vaccine against the delta variant in Israel is unclear.