COVID-19 vaccine boosters may be necessary. Here's what you need to know

Vaccine makers are preparing for a next possible phase of the Covid-19 vaccine rollout: booster doses. Currently three coronavirus vaccines are authorized for emergency use in the United States -- the two-dose Pfizer/BioNTech vaccine for people 12 and older, the two-dose Moderna vaccine and the single-dose Johnson & Johnson vaccines for everyone 18 and older.