As the novel coronavirus sweeps the world, sickening hundreds of thousands of people and killing at least 50,000 individuals to date, scientists have learned more and more about it. We know that older adults — age 60 and above — are at greater risk of dying from it. And, based on data from China, Italy and South Korea, we also know that men seem to have higher fatality rates.

But in the United States, where ramped-up testing is churning out reams of data by the minute, there’s one thing we’re not monitoring: the sex breakdown. How many women are infected vs. men? Are men and women equally likely to get infected? What is the fatality rate for each sex? Are symptoms exactly alike for men and women?

The latest update on U.S. cases and deaths from the Centers for Disease Control and Prevention contained no mention of male and female patients. When asked why, a spokesperson for the CDC said the agency simply does “not have that information to share at this time” and “additional investigation is needed.” Even the New York Times’ case tracker, which was made public last week and provides county-level data, has no sex breakdown because that information isn’t consistently available across states and counties.

“We can confidently say from the data from many countries that being male is a risk factor,” said Sabra Klein, a scientist at Johns Hopkins Bloomberg School of Public Health who studies sex difference in viral infections. “That in and of itself should be evidence for why every country should be disaggregating their data. But the United States isn’t doing it.”

This kind of information — or lack thereof — matters because men and women are likely to have fundamentally different reactions to the virus, vaccines and treatment, health experts say. Indeed, research has shown that the severe acute respiratory syndrome, influenza, Ebola and HIV viruses all affect men and women differently.

“Researchers have found sex differences in every tissue and organ system in the human body,” including the immune system, wrote Caroline Criado Perez in her award-winning book “Invisible Women.”

A recent research paper from Huazhong University of Science and Technology in Wuhan, China, backs that up: Scientists studied the plasma of 331 confirmed coronavirus patients and found that in the most severe cases, women had a higher level of antibodies than men. Although the paper hasn’t been peer-reviewed, it provides yet another reason to capture sex data.

Despite this, the coronavirus vaccine trials underway in the United States aren’t really considering sex yet, said Klein.

The National Institute of Allergy and Infectious Disease — a part of the National Institutes of Health — is running phase one trials of a potential vaccine on 45 healthy adults. The purpose of phase one trials is to “learn about safety and identify side effects,” according to the agency’s website. It is also at this stage that researchers determine the correct dosage for a vaccine.

But the trials of this vaccine will explore age and sex only “as part of subgroup analysis” because “a larger number of participants would be needed to conduct a meaningful analysis of sex and age differences,” the agency said in a statement.

“NIAID is developing plans for potential larger-scale clinical trials,” the statement said.

This approach can be dangerous. Between 1998 and 2000, women represented just 22% of initial small-scale safety trials for new drug applications submitted to the Food and Drug Administration, according to the U.S. Government Accountability Office. The same agency also found that eight of the 10 FDA-approved drugs that were withdrawn from the market from 1997 to 2001 “posed greater health risks for women than men,” including causing valvular heart disease and liver failure.

On the other hand, Johnson & Johnson, which is pushing to get clinical trials of a vaccine started by September, said it would analyze data by sex and age from phase one onward.

Sex data blind spots can be traced back to the fact that, historically, science didn’t study the female body.

“It’s been assumed that there wasn’t anything fundamentally different between male and female bodies other than size and reproductive function,” wrote Perez, so anything that deviates from the “default” — a white, male archetype — is considered an anomaly. Moreover, researchers often argue that the female body is “too complex” to be studied, with its “fluctuating, ‘atypical’ hormones.”

As a result, for years women have been underrepresented in medical research, clinical trials for drugs and vaccines and biology textbooks. Even in 2015, in one of the tests of the so-called “female Viagra” — a product clearly designed for women — scientists tried out the drug on 23 men and two women, wrote Perez.

In 1990, the NIH established the Office of Research on Women’s Health. And in 1993, U.S. lawmakers required the NIH to include more women and minorities in clinical research and trials.

But the NIH has been slow to enforce those rules. A 2015 report by the Government Accountability Office found that although more women than men were enrolled in trials overall from 2005 to 2014, it was unclear whether women were sufficiently represented in all research areas, leaving open the possibility that they may still have been underrepresented in some studies.

And in 2016, the ORWH noted that preclinical trials on animals still “rely heavily on male animals and/or omit reporting of the sex” and added that all researchers applying for funding from 2017 onward must provide a “strong justification” for studying just one sex.

But these regulations apply only to federally funded research, which in 2015 accounted for 22% of total spending on medical and health research, according to a think tank that advocates increased funding for research and development.

“These notions that, ‘I’ve never done this for any other clinical trial. Why am I going to do this today?’ — these things get ingrained,” said Klein, and so any shift in procedure and culture “is perceived as an added complication.”