Here's what we know about possible COVID-19 vaccine booster shots

The U.S. hasn't yet managed to get 70% of Americans vaccinated with at least one shot against COVID-19 — a Biden administration goal — but the federal government and drug makers are already planning ahead for a possible booster shot later this year. 

Other countries, like Israel, started this week to administer a third vaccine dose to bolster the immunity of those vulnerable to SARS-CoV-2, the virus that causes COVID-19.  Pfizer and Moderna are looking at new potential vaccine formulas tweaked to target mutations like the rapidly spreading Delta variant first spotted in India. However, so far, the data show that full vaccination is sufficient to protect against Delta and other variants. Early results also suggest a third shot of the vaccine, virtually identical to the first two doses, might provide a boost in protection.