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Study: COVID-19 Pneumonia Lasts Longer, Causing More Damage Than Regular Pneumonia

Doctor looking at x-ray of a patient's lungs.

Prapass Pulsub / Getty Images

Key Takeaways

  • In a new study, researchers at Northwestern University found that SARS-CoV-2, the virus that causes COVID-19, advances through the lungs over a period of days or weeks by hijacking immune cells. 
  • COVID-19 pneumonia lasts longer than many other types of pneumonia.
  • The researchers theorize that the long duration of COVID-19 pneumonia means it can inflict greater damage on the lungs than other types of pneumonia. 

In a new study, researchers at Northwestern University found that COVID-19 pneumonia differs from other types of pneumonia—often lasting longer and causing more damage.

Pneumonia—defined as an infection of one or both lungs caused by the activity of a virus, bacterium, or fungus—can manifest as exhaustion, chest pain, and shortness of breath, among other symptoms. It develops as pathogen molecules colonize large sections of the organ(s), sometimes within a matter of hours.

But according to the Northwestern researchers, SARS-CoV-2, the virus that causes COVID-19, neither employs this methodology nor adheres to this timeline.

“Our work suggests that the ways in which the immune system responds to SARS-CoV-2 are unusual compared with other causes of pneumonia," Benjamin Singer, MD, senior study author and an assistant professor in the division of pulmonary and critical care medicine at Northwestern University Feinberg School of Medicine in Illinois, tells Verywell. "In particular, the types of immune cells that respond to the infection in the lung appear to be peculiar to COVID-19." The January study was published in the journal Nature. 

What This Means For You

If you contract COVID-19 and develop pneumonia, you may be sick for a longer period of time than you would normally experience with common pneumonia. The best way to prevent negative outcomes from COVID-19 is by following safety precautions like wearing a mask and social distancing.

How Does SARS-CoV-2 Behave in the Lungs? 


For the study, researchers compared lung fluid taken from 88 people with COVID-19 pneumonia, 211 people with non-COVID-19 pneumonia, and 42 people without pneumonia, all of whom were mechanically ventilated. Singer and colleagues determined that SARS-CoV-2 takes a more measured approach to the task of infecting than many of its peers.

It is “slowly-progressive” and “spatially-restricted” while other infections move at a rapid-fire pace and spread expansively. Once established in several small sections of the lung, the virus hijacks immune cells such as T cells and macrophages and uses them to acquire more territory without attracting suspicion.

“The model we propose involves communication between two types of immune cells in the lungs of patients with severe COVID-19—infected macrophages and T cells," Singer says. "The communication between these cell types forms a type of circuit or feedback loop that takes time to develop and also slowly amplifies over time, resulting in a prolonged duration of lung inflammation."

Duration of COVID-19 Pneumonia

It’s a stealthy strategy, but a slow one, too. Unlike other types of pneumonia, the researchers wrote, COVID-19 pneumonia “is characterized by a long duration between symptom onset and the development of respiratory failure”—two to four times that of influenza pneumonia. 

“In most patients, after 10-14 days, the virus can no longer be cultured from airway or lung secretions, yet the immune response persists,” Bruce D. Levy, MD, chief of the division of pulmonary and critical care medicine at Brigham and Women’s Hospital, tells Verywell. 

The consequences can be serious.

“The impact of the longer duration of the viral pneumonia is experienced by the patient as prolonged symptoms, typically cough[ing], chest tightness, and shortness of breath, especially with exertion," Levy says. "A longer duration for the lung inflammation can lead to some lung destruction and ultimately scarring of the lung, which in its most severe form can compromise lung health."

If you reach this point, Singer says, you’ll likely be admitted to the intensive care unit for “a long period of time, usually weeks.” But the ICU has its own pitfalls. People on life support are susceptible to additional complications, including new cases of pneumonia. Even those who manage to dodge secondary infection often emerge in poor physical health. 

Treating COVID-19 Pneumonia

While COVID-19 pneumonia lasts longer than other types of pneumonia, it is often less severe, meaning that the risk for complications is higher but the mortality rate is lower. 

Doctors have responded to COVID-19 pneumonia’s curious clinical features by relying on “supportive interventions,” according to Singer, as well as developing specific treatment strategies. Those strategies may include the intravenous delivery of the antiviral agent remdesivir or the corticosteroid dexamethasone. To date, remdesivir remains the only drug to have been formally approved by the Food and Drug Administration for the treatment of COVID-19 that requires hospitalization.

Both remdesivir and dexamethasone are recommended for use in people who are hospitalized and require supplemental oxygen or ventilation. But the best way to avoid COVID-19 altogether is to follow public health guidelines, Levy says.

“I encourage...readers to get vaccinated for COVID-19 and to practice social distancing, wear a face mask, and wash their hands frequently because an ounce of prevention is definitely worth a pound of cure with COVID-19 viral pneumonia,” he says. 

Regardless of how much we stay indoors or how many bottles of hand sanitizer we polish off, SARS-CoV-2 is probably here to stay. The end goal of his research, Singer told Northwestern, is not to eradicate the virus but to improve its prognosis.

“This study will help us develop treatments to reduce the severity of COVID-19 in those who develop it," he said.

Indeed, the Illinois university’s healthcare system, Northwestern Medicine, already has plans to test an experimental drug designed to target T cells and macrophages in people with COVID-19 pneumonia. A clinical trial is scheduled for early 2021.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

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Article Sources
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  1. Johns Hopkins Medicine. Pneumonia.

  2. Paul M. Why COVID-19 pneumonia lasts longer, causes more damage than typical pneumonia. Northwestern University. January 11, 2021. 

  3. Grant R, Morales-Nebreda, L, Markov N, et al. Circuits between infected macrophages and T cells in SARS-CoV-2 pneumonia. Nature. 2021. doi:10.1038/s41586-020-03148-w

  4. National Institutes of Health. Therapeutic management of patients with COVID-19. Updated December 3, 2020.