Almost since the beginning of the pandemic, doctors believed they knew the most dangerous COVID-19 risk factors.
They were thought to be old age, obesity, diabetes, and lung, heart, and kidney illnesses.
But a major new Harvard University study has uncovered a previously unknown risk factor that make people far more vulnerable to getting a severe case of COVID. It analyzed the medical records of nearly 17,000 coronavirus patients.
Researchers discovered that people who’ve had pneumonia at any time in their lives are at even greater risk than those with diabetes, heart failure, kidney disease, or lung illnesses.
The only risk factor found to be more dangerous than a history of pneumonia was old age.
Nearly half of the people who died from COVID had a history of pneumonia, the study found.
Previous Bout with Pneumonia Is a Major COVID Risk Factor
The chart below from the study lists coronavirus risk factors in order of most to least dangerous.
You may be wondering why obesity isn’t listed. It is a known COVID risk factor. But it was not covered by the study, which was based on patient hospital records. Obesity is often not listed in patient records as a comorbidity—only the conditions it causes, such as diabetes and high blood pressure.
Pneumonia is extremely common. More than 1.3 million Americans are diagnosed with it every year. It is an inflammation of the air sacs in one or both lungs caused by an infection. Patients often develop a cough, wheezing, and have difficulty breathing. 
It can be caused by bacteria, viruses, or fungi. The most common cause is the strep bacteria (Streptococcus pneumonia).
The researchers don’t know for sure why people who’ve had pneumonia are susceptible to severe COVID-19. But people with a history of pneumonia—even if it was many years earlier—may have permanent lung impairment that makes them less able to fight off coronavirus when it attacks their lungs.
People who know they’ve had pneumonia should make it a priority to get vaccinated, said study author Zachary Strasser.
“Let’s get people to self-identify and get to the vaccine clinics,” he said.
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