Last week I saw a tweet by Seth Masket saying "correlation of Biden vote share and adult Covid vaccination rate is now at .847." In the early stages of vaccination, there wasn't much relationship--I recall hearing that West Virginia was one of the leaders. So when did it appear? Our World in Data has data on the number of doses administered over time (originally from the CDC). Since their data included all ages, I divided by the total population. The relationship on July 14:
The District of Columbia is an outlier: the correlation is .81 if you include it and .84 if you don't. Masket didn't, but I don't know any particular reason to leave it out, so I'll include it from now one. A summary history of the correlation:
Feb 1 -.02
Mar 1 .03
April 1 .36
May 1 .70
June 1 .81
June 14 .81
The correlation between the Biden share and vaccinations done in the month was 0.58 for March, .8 for April, .86 for May, and 0.7 for June. Why did the correlation emerge? One possibility is that state governments in Democratic states encouraged vaccinations, but adding the governor's party didn't improve the predictive power. Of course you could try to improve the measure, for example by including control of the state legislature. Still, the idea that the relationship directly reflects individual partisanship (amplified by the influence of friends and neighbors) seems more promising. A Quinnipiac survey from December 2020 asked "If a COVID-19 vaccine is approved by government health officials, do you think you would be willing to get vaccinated, or not?" 80% of Democrats and only 50% of Republicans said they would. What accounts for the difference in willingness to get the vaccine? The survey also asked "how confident are you in the federal government's ability to oversee the safety of COVID-19 vaccines" and there was essentially no difference between Democrats and Republicans (Independents were a bit less confident). It also asked if you or someone you know had been infected--Democrats were more likely to say yes, but the difference was small (77% to 70%). It seems that Republicans were just less likely to think that coronavirus was a serious problem--they were less concerned that they or someone they know would be infected (21% vs. 73% "very concerned")--and less likely to think that the situation was getting worse--34% vs. 87%. The results for "getting worse" are particularly striking, since those kind of opinions usually shift immediately after the election--that is, answers are influenced by confidence in the president-elect.
That raises the question of why state differences in vaccination rates didn't appear right away. I would guess that it was because in the first couple of months vaccinations were mostly limited to people over 65, who were considerably more interested in the vaccine (76% willing to take it, and most of those interested in getting it right away). So at that point differences in vaccination rates had more to do with organization and opportunity.
[Data from the Roper Center for Public Opinion Research]