At first, responses were mostly favorable. In early May, 55 percent of Americans said yes, they would get vaccinated. But that number shrank in each subsequent survey, slipping to 50 percent in late May and 46 percent in early July.

Now the latest Yahoo News/YouGov poll, conducted July 28 to 30, shows that just 42 percent of Americans plan to get vaccinated for COVID-19 — the smallest share to date.

The outlook for universal vaccination is clouded by political considerations from both sides: skepticism about medical authority and expertise on one side (more common among Trump supporters), and suspicions on the other (mostly on the part of Democrats) that the administration is cutting corners on safety to rush a vaccine into production before the election.

Together, these forces threaten to undermine COVID-19 vaccination in the U.S.