Well! That explains a lot, doesn't it? Via NBC News:

Polling showing that a majority of President Donald Trump’s voters support vaccines was shared with several Republicans lawmakers’ staffers in a closed-door meeting Wednesday, according to two people familiar with the meeting.

NBC News obtained a copy of a memo, dated Aug. 26, summarizing the poll results. It was conducted by veteran Republican pollsters Tony Fabrizio and Bob Ward and concluded “that there is broad unity across party lines supporting vaccines such as measles (MMR), shingles, tetanus, diphtheria and pertussis (TDAP), and Hepatitis B.” Fabrizio and Ward presented the findings during the meeting, the sources said.

[...] The poll results may explain the shift in tone from some GOP senators at Health Secretary Robert F. Kennedy Jr.’s hearing Thursday before the Finance Committee.

[...] While the poll showed Trump voters support most vaccines, it also found lingering partisan divides over Covid vaccines. Only 22% of Trump voters said it was important for people to get the Covid shots, according to the poll.

The memo said, however, that “Republicans should not mistake skepticism over the COVID vaccine as evidence that Republican voters are against all vaccinations.”

So MAGA has done a particularly effective job spreading conspiracy theories about covid vaccines. It's gonna be a long winter!