Why some cases of COVID-19 are more severe than others

• Based on the data we have so far, the consensus among experts is that people who are older, immunocompromised, or have significant underlying conditions are more likely to experience severe COVID-19 symptoms.
• A growing body of research suggests gender, race, genetics, and other factors may also impact a patient's outcome.
• "Unhealthy lifestyle habits can absolutely increase your chances of experiencing more severe symptoms," Ramzi Yacoub, chief pharmacy officer at SingleCare, told Business Insider.
• Visit Business Insider's homepage for more stories.

One of the big mysteries surrounding the current pandemic is why some people who test positive for the novel coronavirus exhibit mild symptoms - or none at all - while others have more severe outcomes.

A February report from the Chinese Center for Disease Control and Prevention based on 72,000 cases found that 81% of COVID-19 patients had moderate symptoms, 14% had a more severe reaction that required hospitalization, and 5% percent were considered critical enough to warrant ICU intervention. Other studies in Europe and the US have presented a similar profile.

Based on the data we have so far, the consensus among medical experts is that people who are older, immunocompromised, or have significant underlying conditions are more likely to experience severe symptoms and poorer outcomes. But COVID-19 has also killed hundreds, possibly thousands, of young people with no apparent underlying health conditions.

Far more data is needed to capably determine what puts someone at higher risk for life-threatening complications from COVID-19.

"This is one of the key areas being studied." Abraar Karan, a professor of internal medicine at Harvard Medical School, told Business Insider. "Aside from age and comorbidities, we don't know."

Heart and lung health may be a factor

A growing body of research suggests that heart and lung function play a role in symptom severity. The study from China, for example, indicated COVID-19's fatality rate jumped from about 1% to 6% in those with lung disease or heart problems.

Another report, from Italy's National Institute of Health, found that of 355 COVID-19 patients who died, 30% had narrowed arteries and 7% had irregular heartbeats.

Immunologist Philip Murphy at the National Institute of Allergy and Infectious Diseases has theorized that variations in the gene carrying ACE2, an enzyme that attaches to the surface of lung and heart cells, may impact how easily the virus can enter those organs.

"If a person has a healthy set of lungs, then getting a serious infection might be survivable," Rishi Desai, chief medical officer for the medical-education site Osmosis, told Business Insider. "A similar infection in someone who has very limited lung or heart function can overwhelm and kill them."

Men are experiencing worse outcomes

Gender is also emerging as a predictor of coronavirus outcomes: In most countries, COVID-19 diagnoses are split fairly evenly between the genders, but fatality rates are much higher for men. In China, for example, 4.7% of men who contracted COVID-19 died, compared to just 2.8% for women. In hard-hit Italy, the disease was fatal for nearly 15% of men, but only 8.2% of women.

Unfortunately, in the US, the CDC's main COVID-19 tools, COVID-Net and its weekly activity tracker, don't provide gender information. States have also been lax in providing such data. But in every country where COVID-19 fatalities are tracked by sex, women have been more likely to survive.

That's not entirely surprising: The X chromosome houses the genes responsible for programming our immune system. So women, who have two X chromosomes, typically have a stronger immune response than men, who only have one.

In March, researchers from China's Huazhong University of Science and Technology found that women with severe cases of COVID-9 had more coronavirus antibodies than equally afflicted men, likely making them more able to fight off the virus.

The role of lifestyle in surviving COVID-19

It's also possible that men are more likely to succumb to COVID-19 because of their habits. The World Health Organization estimates, for example, that 34% of men over the age of 15 smoke cigarettes worldwide, compared to only 6% of women.

"Unhealthy lifestyle habits can absolutely increase your chances of experiencing more severe symptoms," Ramzi Yacoub, chief pharmacy officer at SingleCare, told Business Insider. "Since COVID-19 directly impacts your lungs, people who smoke are at a higher risk, due to how harmful smoking is to your lungs and heart."

Alcohol consumption can contribute to liver disease, a risk factor for developing severe coronavirus outcomes, according to the CDC. The typical American male drinks four gallons of alcohol a year, compared to two for women.

America's obesity epidemic may also impact outcomes, University of Minnesota infectious disease expert Dr. Michael Osterholm said.

"We know that about 45% of the US population over the age of 50 is obese," Osterholm said in a March radio interview with WCCO. "I worry that we are going to see a major increase in case fatality rates here in this country, compared to what's been seen in some other countries in the world, just because of that somewhat unique risk factor to us in the US."

COVID-19 is disproportionately killing black Americans

Although they account for 18% of the US population, African Americans represent a third of all US COVID-19 hospitalizations, according to new CDC data. White people represent 59% of the US population, but only 45% of hospitalizations.

In an analysis of 14 states, the CDC found that African Americans are also dying from the virus at alarmingly disproportionate rates. In hard-hit New York City, African Americans have been twice as likely to die from COVID-19 than whites, while in Chicago, 72% of recorded virus-related deaths were among African Americans, though they comprise just 32% of the population.

Data suggest the risk of a severe coronavirus outcome is increased by high blood pressure, diabetes, and asthma- all conditions more prevalent among black Americans. According to the US Department of Health and Human Services, nearly a third of African American adults have high blood pressure, compared to 24% of white adults.

But African Americans are also less likely to have health insurance than whites, making them more reticent to take on the cost of health services, according to a National Institutes of Health study. The NIH also found that African Americans have less access to quality healthcare, creating a higher likelihood of severe outcomes, regardless of the illness.

"The severity of this disease in the African American community is a crisis within a crisis," Wisconsin Gov. Tony Evers said, according to the AP.

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, acknowledged in a White House briefing on Tuesday that people of color may have more comorbidities than white counterparts. But he added there is a duty to investigate the role of stigma and discrimination.

"When you're in the middle of a crisis, like we are now with the coronavirus, it really does, ultimately, shine a very bright light on some of the real weaknesses and foibles in our society," Fauci said. "So when all this is over - and as we said, it will end, we will get over coronavirus - but there will still be health disparities, which we really do need to address in the African American community."

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