Federal health officials announced Wednesday that the public will have access to an extra dose of a Pfizer or Moderna COVID-19 vaccine as soon as mid-September, citing evidence that protection against the virus wanes over time.

“Based on our latest assessment, the current protection against severe disease, hospitalization, and death could diminish in the months ahead, especially among those who are at higher risk or were vaccinated during the earlier phases of the vaccination rollout,” said Biden administration officials including Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, and Dr. Anthony Fauci, chief medical adviser to President Joe Biden.