With viruses like flu and coronavirus, pneumonia often delivers the fatal blow

When people die of the flu — or the new coronavirus, now called COVID-19 — it’s often a lung infection or pneumonia that actually leads to the death.

Facts about the new virus are still frustratingly sparse, but infectious disease experts said there appear to be key differences in the type of pneumonia that COVID-19’s victims get that could make it harder to treat than flu-related pneumonia.

For flu pneumonia, we’ve got prevention — flu and pneumonia vaccines — as well as antiviral and antibacterial medicines. For coronavirus pneumonia, we’ve often got nothing other than what doctors call “supportive care.”

Pneumonia is an infection of the lungs that can be caused by viruses, fungi or, most often, bacteria. Inflammation causes the tiny air sacs in lungs to fill with fluid, making it difficult to breathe and get oxygen into the blood. According to the U.S. Centers for Disease Control and Prevention, about a quarter of a million Americans are hospitalized each year for pneumonia and 50,000 die. Any respiratory virus, including flu, respiratory syncytial virus, and human metapneumovirus, can lead to pneumonia.

On Monday, Sylvie Briand, director for global infectious hazard preparedness for the World Health Organization, said that about 15% of people with COVID-19 have “severe disease with pneumonia that requires hospitalization” and 3% to 5% need intensive care. More than 80% have a mild disease.

Infectious disease experts said those numbers will likely change as more information emerges; the percentage of mild cases will probably increase. “There’s a severity bias,” said Amesh Adalja, infectious disease doctor at the Johns Hopkins Center for Health Security and a spokesperson for the Infectious Diseases Society of America. That means that Chinese doctors are less likely to know about or test people with mild symptoms.

Flu’s death rate is usually less than 0.1%, said Catharine Paules, an infectious disease specialist at Penn State Health Milton S. Hershey Medical Center. The current estimated death rate for COVID-19 is 2%, she said.

Both very young children and very old people are at higher risk for pneumonia, said Ron Collman, professor of pulmonology and microbiology at the University of Pennsylvania’s Perelman School of Medicine. Smokers are also more likely to get it, along with people with chronic lung disease, diabetes, or compromised immune systems.

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So far, there has been little talk of children with COVID-19 in China, a fact that intrigues virus experts. When it comes to flu, children are far better at spreading the virus than adults. They produce more of it and can spread it for more days than adults. “One of the striking epidemiologic features of this coronavirus is how little the pediatric population is involved,” said William Schaffner, infectious diseases specialist at Vanderbilt University Medical Center.

While flu virus can cause pneumonia directly, Schaffner said the “vast majority” of flu-related lung infections are caused by bacteria that move in after flu has weakened defenses in the respiratory system. Often, the bacteria that cause these infections are covered by pneumococcal vaccines, which are recommended for children under age 2, adults 65 and older, and some people in between, he said.

Adalja and John Zurlo, chief of the division of infectious diseases at Jefferson Health, think viral flu pneumonias may be more common than Schaffner does. If someone gets pneumonia early in the course of influenza, that’s likely a sign the virus is to blame, they said. If a patient gets pneumonia after seeming to recover a bit, the culprit is more likely bacteria.

Collman said it can be difficult to tell the two types of pneumonia apart. “It sometimes is really hard to tell … where the pneumonia effects of the virus begin and where the pneumonia effects of the bacteria begin.” Typically, he said, the worst cases are caused by bacteria. “Basically, you have two infections that feed off each other.”

Because it’s hard to tell quickly what’s causing the pneumonia, most patients are treated with antibiotics, Collman said. The primary antiviral medicine that doctors use for influenza viral pneumonia is Tamiflu, but Zurlo said there is “relatively little data about its effectiveness” for pneumonia.

In the U.S., the “overwhelming majority” of healthy people survive pneumonia, Collman said.

Bacterial infections sometimes spread to the blood, though, making patients even more critically ill. Pneumonia can lead to lung or kidney failure. The virus itself, or the inflammatory response it instigates, can also attack heart muscle or the brain, Schaffner said.

Flu makes people more vulnerable to heart attacks and strokes for three to six weeks after they appear to have recovered, he said, possibly because of inflammatory damage to blood vessels. Inflammation is part of our bodies’ responses to invading germs, but too much of it is harmful. “It’s kind of like collateral damage in war,” Schaffner said. “Occasionally, we shoot our friends or civilians.”

In a worst-case scenario for pneumonia, people die because the damage to their lungs is so severe that even mechanical ventilation can’t get enough oxygen into the body, Collman said. Some may also die of sepsis and shock.

The evidence so far points to the virus itself as the cause of pneumonia in COVID-19 patients, the infectious disease doctors agreed. To be sure of that, Schaffner said, “we need more clinical information and very careful observation.” There are no treatments for that virus, although there’s a rush to test drugs used for other viruses like HIV. Because pneumonia vaccines target bacteria, they would not prevent pneumonia caused by a virus. Antibiotics also would not be effective.

Zurlo said Chinese doctors are treating most COVID-19 pneumonia patients with antibiotics, but it’s unknown whether that’s doing any good. Adalja said there have been cases of secondary bacterial pneumonia.

In other coronaviruses, such as MERS and SARS, researchers hypothesize that over-active immune reactions are what cause pneumonia later in the course of the illness, Paules said.

For now, the treatment is supporting patients with extra oxygen or mechanical help with breathing, if necessary, along with careful monitoring of other organs for problems that can be treated. Patients may also need fluids and medicines against nausea and fever, Adalja said.

Going forward, it will be important to identify which COVID-19 patients are at highest risk for pneumonia and pay special attention to them, Paules said. “They may be somebody that you’d have a lower threshold for admitting them to the hospital,” she said.

Zurlo said hospitals are getting ready for wider spread of the new virus in this country. “We’re fully preparing for that possibility,” he said.