When Pfizer in early July announced intentions to file for US Food and Drug Administration (FDA) authorization of a third, booster dose in addition to its two-shot COVID-19 vaccine regimen, the Centers for Disease Control and Prevention, the FDA, and the National Institutes of Health were quick to issue a joint statement saying that they would decide when the timing is right for Americans to have a third immunization.
The agencies stated, in part, “We are prepared for booster doses if and when the science demonstrates that they are needed.”
Since then, Pfizer has announced data suggesting a gradual “declining trend in vaccine efficacy” over 6 months after study participants received two doses of its vaccine, though protection against serious illness and hospitalization remained strong. Breakthrough infections in vaccinated people, particularly with the Delta variant of SARS-CoV-2, have also received growing attention.