Pfizer's CEO Albert Bourla on Thursday, People are likely to need a third dose of a Covid-19 vaccine within a year of getting fully vaccinated and may subsequently need annual shots to protect against the coronavirus.

Pfizer and its German partner, BioNTech, are studying how long the vaccines' protective immunity will last. Their findings will guide whether additional booster shots will be necessary.

Pfizer and BioNTech said this month that data from clinical trials suggest that their vaccine offers high levels of protection six months after the second dose, with no serious safety concerns. The vaccine was also found to be effective against several known coronavirus variants, including one that was first reported in the U.K. and another that was thought to have emerged in South Africa.

Reportedly, Moderna is, in the same way, studying an upgraded version of its Covid-19 vaccine that is specifically designed to target the South African variant, which some experts worried may evade existing vaccines.

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