The CDC is poised to let people get a different booster than their primary shot. Experts say it will give doctors and states flexibility, and smooth over confusing messages over boosters.

However, public health officials have expressed concern about more transient populations, like migrants and the homeless, who received the one-shot regimen of the Johnson & Johnson vaccine. These groups, experts say, may be harder to reach for a second dose.

States are ready to go find those people, but acknowledge it could be difficult.

“We very well might miss some of those people in this next round, but we continue to work on ways that we can provide access and messaging, so that you know we are able to connect to people,” West Virginia COVID czar Clay Marsh said.

Other medical professionals hope that the federal government issues a more nuanced guidance on mixing booster shots, with a focus on receiving a dose of a person’s original series.

Experts said if people need a booster, they may be better off getting the same vaccine as their initial series. But in some places, like nursing homes, access to the original vaccine may not be possible.

Federal officials have been trying to balance the differing and sometimes contradictory messages surrounding the Biden administration’s booster campaign. While the administration initially told the public everyone over the age of 18 who wanted a booster could get one, the reality is more complicated.