You get viral pneumonia when a respiratory virus, most often one you’ve caught through airborne droplets or contaminated surfaces, spreads from your upper airways down into your lungs. It’s not a separate illness you “catch” directly. Instead, it develops as a complication of a common viral infection like the flu, COVID-19, or RSV when the virus manages to reach and inflame the deep air sacs in your lungs.
Which Viruses Cause It
The most common culprits are viruses you’ve likely encountered or heard of: influenza, RSV, COVID-19, human parainfluenza virus, human metapneumovirus, and even rhinovirus (the ordinary common cold virus). Less commonly, adenovirus, chickenpox, and measles can lead to pneumonia as well.
The scale of these infections is significant. During the 2024-2025 respiratory season in the United States alone, COVID-19 was associated with an estimated 290,000 to 450,000 hospitalizations and 34,000 to 53,000 deaths, while RSV accounted for 190,000 to 350,000 hospitalizations and 10,000 to 23,000 deaths. Most of these hospitalizations involved pneumonia or lower respiratory complications.
How a Virus Reaches Your Lungs
Respiratory viruses typically enter through your nose or mouth when you breathe in droplets from an infected person’s cough, sneeze, or even conversation. They can also spread when you touch a contaminated surface and then touch your face. This initial step is ordinary infection, the same process behind any cold or flu.
What turns a routine respiratory infection into pneumonia is a second stage. The virus first multiplies in the lining of your upper airways: your nose, throat, and windpipe. From there, it can travel deeper into your lungs through infected airway secretions or, less commonly, through your bloodstream. Once the virus reaches the tiny air sacs where oxygen exchange happens, it triggers inflammation. Fluid and immune cells flood into these sacs, making it harder to breathe and reducing how much oxygen gets into your blood.
Not every respiratory infection progresses this way. Most people fight off the virus in the upper airways and recover with nothing worse than cold or flu symptoms. Pneumonia develops when the virus overwhelms local defenses or when the immune response itself causes excessive damage to lung tissue.
Who Is Most Vulnerable
Age is the single strongest risk factor, and it works at both ends of the spectrum. Adults 65 and older face increased risk, and that risk keeps climbing with age: an 80-year-old is more vulnerable than a 65-year-old. Children under 5 are also at higher risk, with younger children more susceptible than older ones. RSV hospitalization rates illustrate this sharply: infants under 12 months were hospitalized at a rate of roughly 1,117 per 100,000, while adults 75 and older were hospitalized at about 427 per 100,000 during the same season.
Beyond age, several chronic conditions raise your risk:
- Chronic lung disease (asthma, COPD, or pulmonary fibrosis)
- Chronic heart disease
- Diabetes
- Chronic liver disease
- A weakened immune system, whether from medications like chemotherapy or conditions like HIV
People with weakened immune systems face the greatest risk overall. Their bodies are less able to contain the virus in the upper airways, giving it a clearer path to the lungs.
How It Feels Different From Bacterial Pneumonia
Viral pneumonia often comes on more gradually than its bacterial counterpart. You’ll typically have several days of cold or flu-like symptoms first: runny nose, sore throat, body aches, mild fever. Then breathing becomes harder, you develop a dry or mildly productive cough, and fatigue deepens. Bacterial pneumonia, by contrast, tends to hit suddenly with high fever, shaking chills, and a cough producing thick or discolored mucus.
A runny nose is actually one of the stronger clinical clues pointing toward a viral cause. People with viral pneumonia are roughly 3.5 times more likely to have a runny nose than those with bacterial pneumonia. Bacterial cases, on the other hand, are more likely to involve an abrupt onset of symptoms and are more common in people over 65 or those with other chronic illnesses. On chest imaging, viral pneumonia tends to show a hazy, “ground glass” pattern rather than the dense white patches typical of bacterial infection.
The Risk of Secondary Bacterial Infection
One of the more dangerous complications of viral pneumonia is a bacterial infection that develops on top of the original viral one. When a virus damages the lining of your airways, it creates openings where bacteria can attach and multiply. The virus also suppresses parts of your immune response, leaving you vulnerable to bacteria like Streptococcus pneumoniae and Haemophilus influenzae that may already be present in your nose and throat.
This is not a rare complication in hospitalized patients. Among patients with viral pneumonia who developed secondary bacterial infections, the overall mortality rate was about 11%. For COVID-19 patients specifically, that figure rose to roughly 15%. A worsening cough, new or returning fever after initial improvement, and thicker or discolored mucus can all signal that a bacterial infection has taken hold.
How to Lower Your Risk
Vaccination is the most effective tool for preventing the viral infections that lead to pneumonia. Flu vaccines reduce the risk of influenza-related respiratory illness by 41% to 86% in most seasons. COVID-19 and RSV vaccines are now available for older adults and, in the case of RSV, for infants and pregnant people to protect newborns. These vaccines don’t guarantee you won’t get infected, but they substantially reduce the chance that an infection will progress to pneumonia or require hospitalization.
Interestingly, pneumococcal vaccines, designed primarily to prevent bacterial pneumonia, also appear to offer some protection against viral respiratory infections. One large trial found that a pneumococcal vaccine reduced hospitalized pneumonia caused by any virus by 22% to 51%, likely because preventing bacterial co-infection helps the body handle viral illness more effectively.
Beyond vaccination, the same habits that reduce any respiratory infection apply here: washing your hands frequently, avoiding close contact with visibly sick people, and staying home when you’re ill yourself. For people in high-risk groups, wearing a mask in crowded indoor spaces during peak respiratory season provides an additional layer of protection.