The US Food and Drug Administration authorized an extension of the shelf life of Johnson & Johnson's Covid-19 vaccine, the company said in a statement Thursday.
The move increases the refrigerated storage time for the vaccine from 3 months to 4 1/2 months, and comes as some states said currently available doses were set to expire at the end of this month, potentially before being used.
"The decision is based on data from ongoing stability assessment studies, which have demonstrated that the vaccine is stable at 4.5 months when refrigerated at temperatures of 36-46 degrees Fahrenheit," Johnson & Johnson said in a statement.
Dr. Mark McClellan, a former FDA commissioner and current Johnson & Johnson board member, told CNN's Poppy Harlow on Thursday it's not known how long the company's vaccines can last when stored.
"The J&J vaccine is one you can refrigerate for a long time but as part of this emergency, we weren't able to take the time to see just how long they could last," he said, adding that those studies are currently ongoing.
It's not clear how many doses of the single-shot Johnson & Johnson vaccine distributed around the country were at risk of expiring before they were used. The pace of vaccination has slowed in recent weeks as nearly half of the eligible US population -- people 12 and older -- is already fully vaccinated. The J&J vaccine is authorized for use in people age 18 and older.
Nearly 11 million doses of the Johnson & Johnson vaccine -- about half of the more than 21 million doses that have been delivered to states and other jurisdictions -- have not been administered, according to data from the US Centers for Disease Control and Prevention.
"It is an issue that there are expiring doses -- I would imagine in every state," a source familiar with the federal vaccination effort told CNN on Wednesday. "However, it's a very small percentage of the overall doses that have been sent to providers -- probably 1-2%."
Still, demand for Covid-19 vaccines has dropped off in the United States, even as other parts of the world are eager to acquire more vaccines. Officials have said the logistics and regulations around moving or sharing doses are a challenge.
"We're working very hard, both at the federal level and at the local level, to do everything we can to make sure that these vaccines can be used and deployed in the very best possible way," Johnson & Johnson Chairman and CEO Alex Gorsky said Wednesday during a Wall Street Journal Tech Health event.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told CNN on Wednesday that the FDA is looking into how to get the vaccines "properly utilized, whether it's utilized in the United States or elsewhere."
Kate Cook, a former senior official at the FDA who now serves as executive vice president of drugs and biological products at the firm GreenHealth Inc. in Washington, DC, said that if a state wants to share its allocated coronavirus vaccine doses with another state, she thinks the move would require a green light from the federal government.
"The bottom line is that shipment and distribution of these vaccines is directed by the federal government," Cook told CNN on Wednesday.
A similar regulatory process could be needed for a state to share extra vaccine doses with another country, but it would be more complex, she said.
"The issue of exporting vaccines to other countries -- that's a huge issue that I think would involve a number of different entities," Cook said.
McClellan, the former FDA commissioner, said the United States' "excess supplies" of the shot exist in case of complications such as emerging variants or demand for a booster shot, and that the US needs to increase vaccine donations to other countries.
"There are logistics to work out -- legal issues and so forth. That's something we need to work on right now," he said. "We need to ramp that up, and hopefully that's something that the US and other countries that have benefited from these vaccines can do to accelerate the end of the pandemic."