The small glass vials used to transport Pfizer-BioNTech's Covid-19 vaccine hold more than the expected five doses — and that's OK.
The Food and Drug Administration said Wednesday night that it was aware of reports that vials were yielding six and sometimes seven doses, and that it was acceptable to use all full doses from each vial.
"At this time, given the public health emergency, FDA is advising that it is acceptable to use every full dose obtainable (the sixth, or possibly even a seventh) from each vial, pending resolution of the issue," the agency said in a tweet.
It is common for vaccine vials to be filled beyond their labeled allotment, experts said.
The FDA added that it is important not to mix any leftover vaccine that does not make up a full 0.3 milliliters, since the vials do not contain preservatives.
Pfizer said in an email that it is working with the FDA on the matter.
The extra doses are a bit of good news for the current Pfizer vaccine supply, indicating that current shipments may be able to vaccinate more people than originally thought.
Dr. David Kessler, a former FDA commissioner, said Wednesday on "The Rachel Maddow Show" that it is not a sign of error in the manufacture and preparation of the vaccines.
"It's not mismeasured," he said.
"It's not sloppiness. It's the way those vials are designed," he added.
Distribution of Pfizer's vaccine first started rolling out last week after the FDA gave it an emergency use approval. Since then many states have received their initial allotments and started vaccinating health care workers.