99 Percent of People Who Had Severe COVID Have This in Common

New research has found a commonality among those with the worst cases.

Over the last year, we have seen more than 33 million people get infected with COVID in the U.S., but these illnesses rarely looked exactly the same. Some people had no symptoms at all and didn't even know they were infected, while others ended up hospitalized and in the ICU. Research has been conducted over the last year to find out why the virus ends up manifesting so differently from person to person, and while we've learned a lot, there's still so much we don't know. One recent study, however, has at least shined a light on one commonality among severe COVID patients: Almost all of them do not end up getting reinfected with the virus.

RELATED: The CDC Says Vaccinated People Who Get COVID Have This in Common.

The study, which was published April 25 in the Clinical Infectious Diseases journal, analyzed the rate of reinfection for patients who had already had COVID. Researchers from the University of Missouri School of Medicine and MU Health Care analyzed more than 9,000 COVID patients with severe illness from 62 U.S. healthcare facilities who were infected between Dec. 1, 2019 and Nov. 13, 2020.

The patients analyzed had at least one instance of COVID-related impatient stay or emergency department visit, and researchers sought to find out how many of these patients got COVID again after surviving a severe bout of the virus. Reinfection was defined as two positive COVID tests separated by two or more consecutive negative tests and more than 90 days after the initial infection ended.

According to the study, only 0.7 percent of the patients with severe COVID ended up being reinfected with the virus, which means that over 99 percent did not end up getting COVID again.

"This is one of the largest studies of its kind in the U.S., and the important message here is that COVID-19 reinfection after an initial case is possible, and the duration of immunity that an initial infection provides is not completely clear," lead researcher Adnan I. Qureshi, MD, professor of clinical neurology at the MU School of Medicine, said in a statement.

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On average, the patients that did test positive for COVID again did so 116 days after their initial infection. Non-white patients made up a higher proportion of reinfected patients and patients with nicotine dependence, tobacco use, asthma, and chronic obstructive pulmonary disease (COPD) were more likely to be reinfected as well.

The researchers also found that reinfection was associated with less severe illness than primary infection. They concluded that there were lower rates of pneumonia, heart failure, and acute kidney injury during reinfection compared to primary infection. So if you do have severe COVID the first time around, you're less likely to have a serious case in the unlikely event that you get sick again. That said, of the reinfected patients, 3.2 percent did not survive the illness.

RELATED: 99 Percent of People Hospitalized for COVID in 2021 Have This in Common.

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