Vaccine efficacy against infection is waning slightly with time – but efficacy against severe symptoms remains strong
Federal health authorities have recommended booster shots for all adults who are fully vaccinated against Covid-19 with either the the Pfizer or Moderna vaccines, citing evidence that suggests breakthrough infections could become more common over time.
The plan has faced scrutiny. Some US scientists have said data was insufficient to support the decision, and vaccines remain highly effective against severe disease requiring hospitalization and death. The World Health Organization harshly criticized US leaders for using vaccines to provide a third shot to people, even as most around the world haven’t had one.
