Vaccine effectiveness means how well the vaccine performs in everyday life for a broad range of people.
Deeper dive
Data from vaccine effectiveness studies looks at the vaccine’s effects in a large, often diverse population, including those who are immune compromised and pregnant.
With COVID-19, the term is widely misunderstood to mean efficacy, which is how well the SARS-CoV-2 vaccine performed in clinical trials. For example, in clinical trials conducted during 2020, the Pfizer/BioNTech vaccine was found to have 95 % efficacy in preventing laboratory confirmed SARS-CoV-2 infection.
However, since 2020, the SARS-CoV-2 virus has mutated resulting in variants of the virus, leading the and the CDC to approve multiple vaccine booster shots for Pfizer, Modern and J&J vaccines. In late summer 2022, the CDC approved a COVID-19 booster that specifically targets the latest variant of the virus, called omicron. See this CDC website for the latest on COVID-19 vaccine effectiveness and safety data.