3. Rationale For COVID-19 Vaccine Booster Doses
Concerns have been raised that declining neutralizing antibody titers or reduced effectiveness against symptomatic disease may herald significant declines in effectiveness against severe disease. The recent emergence of the highly transmissible Delta variant of SARS-CoV-2 resulted in a new wave of COVID-19 cases in many parts of the world and has led to considerations for administration of booster doses to individuals who received primary series of vaccines in an effort to enhance immunity, and thus sustain protection from COVID-19.
The expected benefit of booster vaccination will depend on the impact that booster vaccination has in reducing disease relative to the primary series. If the primary series of Moderna COVID19 Vaccine is still effective in preventing important COVID-19-related outcomes, then the benefit of booster vaccination is likely to be more limited than if effectiveness following the primary series has waned substantially. Factors supporting authorization of a booster dose should consider the effectiveness of primary vaccination with Moderna COVID-19 Vaccine over time and against circulating variants, the effectiveness (and its duration) of booster vaccination in preventing important COVID-19-related outcomes (including death, hospitalization, and infection with SARS-CoV-2 followed by long COVID-19) in individuals who have already received a 13 primary vaccination series, the dynamics of the pandemic in the United States, and the risks of booster vaccination in the general population or in certain subpopulations.
Some real world effectiveness studies have suggested declining efficacy of Moderna COVID-19 Vaccine over time against symptomatic infection or against the Delta variant, while others have not. However, overall, data indicate that currently US-licensed or authorized COVID-19 vaccines still afford protection against severe COVID-19 disease and death in the United States. There are many potentially relevant studies, but FDA has not independently reviewed or verified the underlying data or their conclusions.