The US Centers for Disease Control and Prevention (CDC) gave the green light for booster doses of Moderna and Johnson & Johnson's COVID-19 vaccines late last month. This follows shortly after the approval of Pfizer's booster shot for those at high risk of severe disease. Along with this endorsement, the CDC also approved a mix-and-match approach to boosters, meaning eligible people can now choose whichever vaccine they wished among the three as a booster.

Health authorities have taken a hands-off approach in recommending which combination would work best, but what does the science say?

A study by the National Institutes of Health (NIH) on 458 patients who tested combinations of Pfizer, Moderna and J&J vaccines found that boosting with a different vaccine is safe. Preliminary data showed that boosters increased antibody levels no matter the combination:

On the other hand, Chinese infectious disease experts have recommended holding off mixing Chinese vaccine booster shots until there is confirmed data. This is despite acknowledging that a mix-and-match strategy may be better than a third jab using the same vaccines. 

Regardless of whether one chooses to mix vaccines or continue with their current vaccine type, it looks like a booster shot may be needed every year, much like the flu vaccine.