Why pneumonia treatments sometimes fail

Pneumonia

Image credit: Mayo clinic research

Pneumonia is the most common infectious cause of death worldwide, responsible for an estimated 2.5 million deaths a year. In severe cases, patients may need to be admitted to an ICU and given mechanical ventilation. Severe pneumonia accounts for 6 in 10 infections managed in intensive care, and spread of the infection within ICUs is a significant concern.
Severe pneumonia is usually diagnosed through a combination of symptoms, imaging and blood tests. Symptoms typically include fever or hypothermia, low oxygen levels, breathing difficulties and confusion.

Pneumonia treatment depends on the underlying cause and severity. Bacterial infections require antibiotics, while viral cases focus on symptom management. Severe illness may require hospitalization for oxygen therapy or IV fluids. Home care involves rest, hydration, and over-the-counter fever reducer

Bacterial Pneumonia: Treated with prescription antibiotics. It is vital to finish the entire prescribed course—even if you feel better—to prevent the infection from returning. 

Viral Pneumonia: Antibiotics are ineffective. Doctors usually focus on managing symptoms, though they may prescribe antiviral medications for certain viruses like influenza. 

Fungal Pneumonia: Treated with specific antifungal medications

Doctors have long struggled to understand why patients whose condition looks similar clinically can have very different recoveries. Some respond quickly to treatment, while others remain critically ill for weeks or even die.
Researchers have now shown that severe pneumonia has three different subtypes, helping explain why some patients in intensive care units (ICUs) recover from their illness faster than others, while for other patients the disease can be life-threatening.
Their findings could in future help inform tailored treatments, allowing individual patients to receive the most appropriate therapies.
Even though doctors are able to treat the initial infection, many patients with severe pneumonia still struggle to come off the ventilator and can develop lung failure. Therapies to tackle inflammation in the lungs have had mixed results in clinical trials—some suggest they are beneficial, others that they're harmful.
The current approach of classifying patients by their clinical syndromes—sepsis, acute respiratory distress syndrome and so on—without looking at the underlying biology risks missing what's key. Instead of asking 'Does this patient have pneumonia?', doctors should be asking 'What's the inflammatory pattern in this patient's lungs to correctly treat them?'"

Instead of relying only on blood tests or scans, however, the research team analyzed immune cells, inflammatory signals and gene activity in fluid taken from the lungs of the patients. They discovered that there are three distinct biological types—or "pneumotypes"—of severe pneumonia, none of which could be reliably detected using standard blood tests, even though they were strongly linked to how patients recovered.

The most common pneumotype—accounting for almost half (49%) of cases—was characterized by immune suppression, significant damage to the lining of the lungs and bleeding in the alveoli (tiny air sacs within the lungs). There were fewer signs of inflammation, which may explain why treatments targeting inflammation can fail or even harm some patients.

The second pneumotype—accounting for just under a quarter (23%) of cases—was characterized by a balanced immune response and active repair of damage to the lungs. Patients were most likely to recover faster from this pneumotype and require the shortest time on the ventilator, even though they initially looked just as ill as the others.

Patients with the most dangerous pneumotype—the one that most resembles "classic" pneumonia—spent the longest on mechanical ventilation and had prolonged critical illness. They had severe and persistent inflammation, with a flood of immature immune cells in the lung. This group may be most likely to respond to anti-inflammatory therapies, the research team said.

Severe pneumonia is not a single disease, but several biologically distinct conditions that happen to look alike. This helps explain why 'one-size-fits-all' treatments—including some immune-modulating drugs—have often failed in clinical trials.

The tests used to determine the pneumotypes are too complex to enable rapid classification, but the researchers hope to develop a simplified tool that could help them stratify the patients and ultimately offer tailored treatments.

Pulmonary inflammation in severe pneumonia is characterised by compartmentalised and mechanistically distinct sub-phenotypes, Nature Communications (2026). DOI: 10.1038/s41467-026-74190-x