Severe Flu And COVID Create The Ideal Conditions For Lung Cancer. The Answer? Vaccines

“A bad case of COVID or flu can leave the lungs in a long-lasting ‘inflamed’ state that makes it easier for cancer to take hold later,” said senior study author Jie Sun, from the University of Virginia School of Medicine, in a statement.

A severe lung infection is bound to leave some damage in its wake, and scientists knew this was the case for COVID and flu, but they weren’t sure what long-term impact this could have. Other published work has hinted at a link between these viruses and cancer – a paper in August 2025 reported that either infection could “reignite” dormant cancer cells and promote the formation of new tumors.

Sun and colleagues investigated the potential link between severe respiratory infections and lung cancer in both mice and humans. 

The lab mice that were infected with SARS-CoV-2 or flu and experienced severe disease were more likely to develop lung cancer afterwards, and significantly more likely to die from it. 

This trend was borne out when the team looked at data from real-life COVID patients – people with a history of hospitalization for COVID saw a 1.24-fold increase in their risk of lung cancer, regardless of whether or not they smoked or had other health problems. 

They can’t rule out that some of those patients may have had pre-cancerous changes before they caught COVID; however, the fact that the mice developed cancer only after the infection suggests the same mechanism is possible in humans too.

From those mouse experiments, the authors concluded that severe infection can alter immune cells within the lungs to create a “pro-tumor” inflammatory environment. There were also changes observed in the cells that form the lining of the lungs and the air sacs.

“We’ve known for a long time that things like smoking increase the risk for lung cancer. The results from this study suggest that we may need to think about severe respiratory viral infection similarly,” said co-author Jeffrey Sturek, MD, PhD.

“For example, in some patients who are at high risk for lung cancer based on smoking history, we recommend close monitoring with routine screening CT scans of the lungs to catch cancer early. In future studies, we may want to consider a similar approach after severe respiratory viral infection.”

In the wake of the COVID pandemic and with severe seasonal flu infections happening every year, the authors suggest there could be “tens of millions” of people around the world who have recovered from a viral pneumonia who could benefit from this extra monitoring.

But there was even more reassuring news from the study, a simple way that some of this extra cancer risk could be mitigated in the first place: vaccination.

“We also believe that vaccines don’t just prevent acute hospitalization after contracting the virus. They may also reduce the long-term fallout of severe infection, including the kind of immune scarring that can increase cancer risk,” said Sun.

When there’s a new medical breakthrough in the lab, it can sometimes be hard to see the path forward to a direct impact on patient care in the real world. In this case, though, the knowledge that patients with a history of serious lung infections could be at a heightened risk of cancer – even if they don’t smoke – could be useful to doctors right now.

“These findings have important immediate implications for how we monitor patients after severe respiratory viral infection,” said Sturek.

The study is published in the journal Cell.