On April 30, the Centers for Disease Control and Prevention reported that 100 million Americans are now fully vaccinated—roughly half the adult U.S. population. More than 147 million have received at least one jab. Vaccination‐​induced immunity combined with the roughly 32 million confirmed COVID cases in the U.S. (the actual number of cases may be several times that number), are why U.S. case and hospitalization rates continue their downward trend, and why some degree of herd immunity may be not far away. As if to add an exclamation point to the good news, Disneyland opened its doors that same day, after being closed for over a year.

The three vaccines available in the U.S. deserve most of the credit for the good news. The unprecedented efficacy and the excellent safety profile of these vaccines should allay the concerns of the vaccine‐​hesitant. Yet a steadfast 20 percent of adults tell a Kaiser Family Foundation survey they refuse to get vaccinated or will only do so if compelled.

Earlier that same week the CDC announced it is safe for fully vaccinated people to walk outdoors without a mask provided they are not in crowded situations. The CDC announcement came in the wake of several studies over the past year showing the risk of outdoor transmission—even among unvaccinated people—is extremely low.

Yet, while walking alone towards my car in a parking lot the other day, I was chastised by a woman who was several yards away from me because I was not wearing a mask. The woman was double‐​masked and also wearing a face shield. I told her about the CDC’s new outdoor mask guidelines and that I was fully vaccinated. The woman replied that she too was fully vaccinated but knows better than to walk outside without wearing a mask. Realizing that there was nothing to be gained from continuing the conversation I got into my car and drove off.

The woman would have agreed with the Brookline, Massachusetts Town Manager, who announced on April 30 that, despite the new CDC guidance, and despite the state easing its outdoor mask mandate, the outdoor mask mandate will remain in place in Brookline.

A recent study from the University of California San Diego found political ideology to be a predictor of both vaccine hesitancy and fear of the coronavirus pandemic. Those who identify as Republicans tend to view the viral pandemic as less threatening and are more reluctant to get vaccinated. Those who identify as Democrats tend in the opposite direction. The researchers point to evidence that both groups are guilty of confirmation bias through differential exposure to media channels and social networks.

To be sure, there are some people who have medical or religious reasons for not getting vaccinated. And there are some who have immune deficiencies or other health reasons for wearing masks outdoors and were doing so before the COVID-19 pandemic. But the focus here is on behaviors specific to SARS‐​CoV‐​2.

Those who wear masks outside when jogging, riding a bike, or driving alone in their cars have something in common with the vaccine‐​hesitant: both groups refuse to let the evidence change their behavior. But here’s where the similarities end: wearing a mask despite overwhelming evidence that it is unnecessary may be pointless, but harms nobody; refusing to get vaccinated despite overwhelming evidence of the vaccine’s safety and efficacy potentially harms others.