For months, local, state and federal officials have been consumed with how to persuade Americans who are wary of the COVID-19 vaccine to get the shot anyway. The conversation has focused in large part on specific demographic groups and how to overcome certain cultural factors to get the vaccines into people’s arms. Experts worried about low turnout among women, who reported significantly more vaccination hesitancy than men prior to the vaccine rollout. And public health officials warned that non-Hispanic Black Americans would be more hesitant than other racial groups because of the historical abuses and exclusion they’ve experienced at the hands of medical professionals and researchers.

But the data on actual gender differences in vaccination rates veered in an unexpected direction, leaving an entire group of vaccine-hesitant Americans largely untargeted: men.

As of Monday morning, the Centers for Disease Control and Prevention reported that nearly 9.5 million more women than men have been vaccinated in the U.S.,1 and in the 42 states2 that collect gender data, a greater share of women are getting the vaccine as well. The magnitude of the gender gap varies from state to state but has hovered just below 10 percentage points on average over the past month.

According to experts and the latest research, the reasons why we are seeing this persistent gap are complicated. On the surface, it’s a matter of which groups were targeted early on, but when we look deeper, other behavioral and ideological divides between women and men appear to be at play. These four hypotheses may explain the imbalance.

Hypothesis 1: Early Access

The simplest explanation for the vaccine gender gap is that women got a head start. Among older Americans, who had early access to the vaccine, women outnumber men: The U.S. Census Bureau estimates that women make up about 55 percent of all adults age 65 and over. And in specific occupational groups with early access in most states, women also outnumber men — among child-care workers and health-care practitioners, for example, women constitute about 95 percent and 74 percent, respectively.

Hypothesis 2: Traditional Masculinity 

COVID-19 isn’t the only health matter that men are less likely to be proactive about. Compared with women, they tend to see a doctor less often and use harmful substances like alcohol and illicit drugs more often; men also tend to eat less fiber and fruit, and they are even less likely to use sunscreen when compared to women.

Hypothesis 3: Preventive Health Behaviors

My conversation with Mahalik led me to ask other scholars about potential differences in how men and women evaluate medical evidence. Jennifer Reich, a sociologist at the University of Colorado Denver who has studied vaccination behavior for more than a decade, told me that women were more used to making decisions about their own health and the health of their families than men were. “Women are accustomed to seeking out health care in the form of reproductive health from a young age on a biannual or annual basis, so much so that women are more primed to be thinking about preventing illness in a way that men tend not to participate in until they’re about 50,” she said.

Hypothesis 4: Political Ideology and Susceptibility to Conspiratorial Thinking 

Scheduling a doctor’s appointment or putting on sunscreen is relatively uncontroversial; getting the COVID-19 vaccine is not. According to national polling from the Kaiser Family Foundation, 29 percent of Republicans reported that they would “definitely not” get the vaccine compared with just 5 percent of Democrats. This divergence could partially explain the vaccine gender gap when we consider gender differences in political leaning. Women are more likely than men to say they lean toward the Democratic party, while men are more likely than women to say they identify as Republicans or independents.

Closing the Gap

Appealing to traditional masculinity, such as framing the vaccine as a way to strengthen the body against the virus, could be one way of closing the gap. That approach may reinforce ideologies that are known to be harmful to men’s health on the whole, but it might be worth the trade-off. “You have to recognize where people are coming from,” said Metzl.

Read the full article about the COVID vaccine gender gap by Angelica Puzio at FiveThirtyEight.