Sanders on Wednesday asked Bancel to reconsider the price hikes, saying they could make it unaffordable for millions of Americans and were unjustified given the government's research contributions and $1.7 billion in assistance in developing the vaccine. His comments echoed his January letter to Bancel.

Bancel said Moderna's next COVID-19 shots will be more expensive because they will be sold in single-dose vials or pre-filled syringes for the commercial market versus the 10-dose vials it has sold to the government up until now.

The government in May plans to end the COVID public health emergency, putting much of the vaccine purchasing in the hands of the private sector.