A US Centres for Disease Control and Prevention advisory panel is expected on Sunday to recommend Johnson & Johnson’s COVID-19 shot for widespread use, a final clearance for the vaccine after it was authorised by US regulators on Saturday.

The Advisory Committee on Immunisation Practices (ACIP) has played a major role in guiding states on how to allocate scarce doses, though states themselves have the final say in how they allocate shots.

For previous COVID vaccines, the CDC panel discussed clinical considerations for patients including pregnant women and people with severe allergies, who were not studied in clinical trials.

A panel vote is scheduled for after 3 p.m. ET (2000 GMT), and the CDC’s director is expected to approve the recommendations by the panel.

State and local public health authorities will use Food and Drug Administration and CDC guidance as they administer the first roughly 4 million doses that the federal government, through distribution partner McKesson Corp, plans to ship Sunday night or Monday morning.

J&J’s shot will be the only one-dose COVID vaccine available in the United States. It is also the easiest to ship and store, as it can be kept in a refrigerator rather than a freezer.

J&J expects to ship more than 20 million doses by March and 100 million by mid-year, enough to vaccinate nearly a third of Americans.