WASHINGTON — Vaccine holdouts could end up being the last obstacle to defeating the pandemic, and a growing effort is aimed at convincing one substantial group of skeptics: Republicans.

While efforts to combat vaccine hesitancy and access have so far been mostly focused on African Americans and Latinos, recent polls suggest the largest group of Americans either hesitant about the Covid-19 vaccine or outright opposed to it are Republicans, and efforts to reach them are only in their infancy.

Success convincing skeptical conservatives could be the difference between the United States reaching herd immunity or not. That's why a group of Republican pollsters and politicians, plus the White House, are all already working on getting the skeptics on board.

Messages targeted at minority groups were overt and discussion of hesitancy among people of color was clear. But when it comes to targeting a partisan population, appearing overtly political opens up new risks and could backfire, those working on the efforts warn.