Recent studies have shed new light on how vaccine effectiveness declines over time and the role of booster doses in maintaining protection. Researchers found that immunity against severe COVID-19 disease starts to wane approximately four months after receipt of the third dose of an mRNA vaccine. This waning was detected during both the Delta and Omicron variant waves, and it was comparable to how mRNA vaccine effectiveness waned after a second dose.
The data also revealed an important disparity: although protection decreased with time, a third dose was still highly effective at preventing severe illness. Furthermore, the study highlighted a social inequality: people who are Hispanic or Black were half as likely to have a third vaccine dose than people who are white, making people who are Hispanic or Black more vulnerable to severe COVID and highlighting the need for public health officials to double down on efforts to protect these vulnerable populations.
The findings confirm the importance of receiving a third dose of mRNA COVID-19 vaccine to prevent moderate-to-severe COVID-19 illness, especially among those with comorbidities, and support the consideration of additional boosters to sustain protection against moderate-to-severe disease.
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