Vaccine advisors for the Food and Drug Administration (FDA) today unanimously approved a third and smaller dose of Moderna's COVID-19 vaccine for vulnerable groups.Today's meeting of the FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) was the first of two days of booster-dose deliberations, which tomorrow will cover the Johnson & Johnson vaccine and mix-and-match strategies.In advance of tomorrow's VRBPAC meetings, a research team based at the National Institutes of Health (NIH) yesterday released a preprint study suggesting that all vaccine combinations were well tolerated and immunogenic, but Johnson & Johnson recipients got a bigger immune response from an mRNA vaccine booster than a second dose of their