Since early 2020, coronavirus variants have evolved that are better able to escape immunity from past infection or vaccination. This has prompted updates to the COVID-19 boosters that better match the components of the vaccine with the circulating omicron subvariants. Updated bivalent COVID-19 boosters are now available.

How well did the original vaccines work to protect against COVID-19?

The original Pfizer-BioNTech and Moderna mRNA vaccines targeted the spike protein from the ancestral strain of SARS-COV-2. Vaccine efficacy was 95% against the early variants that circulated in 2020 and early 2021. The effectiveness declined slightly with the emergence of the delta variant in the summer of 2021.

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