Every critical care specialist attending COVID-19 patients in the intensive care unit where I have been filling in as an intensive care physician for the past two weeks makes the same observation: Our patients seem almost universally obese, while most ill but stable patients elsewhere in the hospital have lower body masses.

Critical care doctors in other parts of the country, as well as my colleagues in Europe, report seeing the same thing.

New research backs up the anecdotal observations. Data from my institution, NYU Langone, shows that body mass consistent with even early obesity in the setting of coronavirus infection makes a patient three times more likely to need intensive care medicine, suggesting a more severe clinical course.

There are many causes of obesity (including genetics, environmental factors, biological traits, social ties and profound changes in the gut microbiome), but its consequences are fairly uniform—including a rise in liver disease as the liver becomes overfilled with fat. Today, obesity is a more common cause of cirrhosis than alcoholism.

Forty-two percent of Americans are obese, according to the CDC — more than any other nation outside of the Pacific island nations and Kuwait.

The 1957 Asian flu pandemic and the 1968 Hong Kong flu pandemic showed that obese people were more often infected and more likely to succumb to the viral infection. More recently, obesity was linked to hospitalization and death rates in the 2009 swine flu pandemic.

Americans have long struggled with weight as a national and individual issue. But in a time of pandemic, America’s weight issue has devastating implications.

Obesity leads to the body’s insulin and glucose levels rising as people become pre- and then fully diabetic. Those individuals are more at risk for cardiovascular disease including hypertension, coronary artery disease and other diseases.

All of these comorbidities or underlying conditions worsen the outlook when a person is infected with coronavirus. But in terms of immune systems, the impacts are much less widely known.

Obese people—even those without known health conditions—have two disadvantages in immunity. One is in the inbuilt immune defense systems, and the other is in adaptive immunity, or the ability to rise up to a new infectious threat and mount a novel immune response.

This dysfunctional immune response is likely part of why we are seeing severe lung injuries with greater need for mechanical ventilation and more critical illnesses in obese Americans infected with the coronavirus.

Animal studies on the influenza virus show that obesity is associated with more severe lung damage, more superimposed bacterial infections and even more worrying, a less robust response to vaccines.

While the focus on the pandemic’s targets has partly been on underlying conditions and more recently on race, perhaps it is prudent to focus on coronavirus’s targets like the virus does: biologically and metabolically.

Research on influenza infections also shows that the obese may be more contagious, by increasing the timeframe in which they continue shedding a virus after an infection, with huge implications for mitigation strategies. It seems likely the same will apply to the coronavirus, because the immune defects are the same.

Scientists have also shown that body mass index—the defining measure of obesity—tracks amount of viral shedding of influenza in exhaled breath, and this is more notable in obese men particularly.

All of this suggests that health care needs to be augmented not just with more screening and treatments but with improved health access and greater health literacy.

Thankfully, weight loss and mild to moderate exercise very quickly restore innate and adaptive immunity to make a person immediately more capable of fighting infection and less vulnerable to being infected. (Though intense exercise, like running marathons, can actually worsen immunity.)

As sedentary activity impairs immunity, during this pandemic and far beyond, health programs to help Americans get on the move can not only improve an individual’s health, but protect against successive waves of coronavirus infection.

Now more than ever, getting into shape has become a matter of urgent national public health security.