A severe case of COVID-19 or influenza may increase your risk of developing lung cancer by 24% in the months or years that follow, according to new research examining data from 76 million adults. The finding suggests that serious respiratory infections do more than cause immediate illness; they can fundamentally change how your lungs respond to cancer development long after you've recovered. How Can a Respiratory Virus Lead to Cancer? Researchers at the University of Colorado and University of Virginia examined how severe lung infections from influenza and COVID-19 might prime the body for cancer. They studied both mice and humans to understand the connection. In mice, scientists found that those who experienced severe lung infections from influenza or COVID-19 were more likely to develop lung cancer later and more likely to die from it. To test whether this pattern held in humans, researchers analyzed health data from 76 million adults across the United States, Lebanon, and Saudi Arabia who had been hospitalized for COVID-19 but had no history of cancer before 2022. They tracked these patients' health records for new cancer diagnoses going forward. The results were striking: people hospitalized with COVID-19 showed a 24% increased risk of lung cancer diagnosis, regardless of whether they smoked, used to smoke, or had other risk factors that typically increase lung cancer likelihood. What Happens Inside Your Lungs After a Severe Infection? The mechanism behind this increased risk involves inflammation and changes to immune cells. When you experience a severe respiratory infection, your immune system mounts a powerful response. However, this response can leave lasting changes in your lung environment that make cancer development more likely. "The findings basically show a 'memory' function within the lung environment. So the environment of the lung seems to be switched because of this infection, and that switch within the lung is more conducive to cancer initiation or progression," explains James DeGregori, PhD, a professor of biochemistry and molecular genetics at the University of Colorado Anschutz School of Medicine and interim director of the University of Colorado Cancer Center. This chronic inflammatory state creates conditions where cancer cells can more easily take hold and grow. The research is particularly significant because it establishes what researchers believe is the first causal link between prior viral infection and lung cancer development. Who Is Most at Risk? While the 24% increased risk applies broadly, certain groups face higher vulnerability to severe respiratory infections in the first place. Understanding who is most susceptible can help guide prevention strategies. - Young Children: Severe illness is most likely during a person's first infection with respiratory viruses, which puts young children at higher risk for complications like pneumonia and bronchitis. - Older Adults: People over 65 face increased vulnerability to severe respiratory infections and are more likely to experience prolonged hospital stays and complications. - Immunocompromised Individuals: People with weakened immune systems, whether from medical conditions or medications, are at significantly higher risk for severe illness from respiratory viruses. Steps to Protect Yourself From Severe Respiratory Infections - Get Vaccinated: Vaccination remains the most effective way to prevent severe COVID-19 and influenza. Experts emphasize that vaccination is critical for reducing both immediate infection risk and potential long-term complications like cancer. - Use Antiviral Medications Early: If you do get infected, talk to your healthcare provider about medications like Tamiflu for flu or Paxlovid for COVID-19. These can prevent a mild infection from becoming severe if taken early in illness. - Practice Basic Hygiene: Wash your hands regularly, avoid touching your face, and keep commonly touched surfaces clean to reduce transmission risk in your household and community. - Avoid High-Risk Situations When Possible: If you're at high risk for severe illness, consider limiting exposure during peak infection seasons or in crowded indoor settings where respiratory viruses spread easily. - Stay Home When Sick: If you develop respiratory symptoms, remain home for at least the first few days when you're most contagious to protect vulnerable people around you. What Should You Do If You've Had Severe COVID or Flu? The research suggests that people with a history of severe respiratory infections may benefit from closer monitoring. "Severe viral infections are not only harmful in the acute phase, but may also contribute to the development of chronic diseases, including cancer. Therefore, it is important to protect ourselves from severe infections whenever possible," says Jie Sun, PhD, a professor of medicine and codirector of the Beirne B. Carter Center for Immunology Research at the University of Virginia School of Medicine. Experts recommend that healthcare providers consider close monitoring of people with a history of severe COVID-19, flu, or pneumonia for lung cancer screening purposes. If you've experienced a severe respiratory infection requiring hospitalization, discuss with your doctor whether additional lung cancer screening might be appropriate for you. The takeaway is clear: while respiratory infections are common and usually resolve without lasting harm, severe cases warrant both immediate treatment and long-term vigilance. Vaccination, early treatment with antivirals, and basic hygiene practices remain your best defense against the immediate and potential long-term consequences of serious respiratory illness.
