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The US has approved Moderna and Johnson & Johnson vaccines to be used as booster jabs, and said Americans can now receive doses of vaccines that are different from the one they initially received.
The green light for mixing-and-matching comes a month after the Food and Drug Administration (FDA) authorised Pfizer booster jabs for some Americans, including those over 65 or at higher risk of severe illness and who work in frontline jobs.
Less than 5% of Americans have so far received a booster jab, according to US health officials.
But with tens of millions of US residents already eligible for a third shot, many remain confused about boosters, who needs them and how they help.
