- Outbreaks in economies that vaccinated early such as Israel and new studies
have raised doubts about the durability of vaccine protection and prompted booster rollouts. How much has the efficacy of major Western vaccines waned over time and how much will boosters help?
- We first show that lower recent estimates of vaccine efficacy against infections
reflect a reduction in the immune response to vaccines over time, higher vaccine resistance of the Delta variant, but also biases in several real world studies.
- Averaging across the most robust studies, we document that vaccine efficacy
against infections tends to diminish significantly over time from around 80% a month after full vaccination to around 55% five months after vaccination. In contrast, vaccine efficacy against symptomatic infections and especially hospitalizations diminishes less over time, with an estimated efficacy against hospitalizations of around 90% six months after vaccination.
- Finally, we document early evidence from Israel which suggests that booster
nshots return vaccine protection against infections to high levels and should raise protection against hospitalizations even higher.