Common cold virus may be able to combat the more dangerous flu by activating body’s defenses, finds study
As the flu season approaches, a strained public health system may have a surprising ally -- the common cold virus. Rhinovirus, the most frequent cause of common colds, can prevent the flu virus from infecting airways by jumpstarting the body’s antiviral defenses, according to scientists. This suggests that the common cold combats influenza.
A Yale team led by Dr Ellen Foxman studied three years of clinical data from more than 13,000 patients seen at Yale-New Haven Hospital, US, with symptoms of respiratory infection. The authors found that even during months when both viruses were active if the common cold virus was present, the flu virus was not. Dr Foxman says when they looked at the data, it became clear that very few people had both viruses at the same time.
“Infection with the common cold virus protected cells from infection with a more dangerous virus, the influenza virus. The protection occurred because the common cold activated the body’s general antiviral defenses, and the effect lasted at least six days. This may also explain why the flu season (winter) generally occurs after the common cold season (autumn), and why very few people have both viruses at the same time. This work may allow us to better predict how respiratory viruses spread and to design interventions for viruses when we do not have vaccines,” Dr Foxman, an assistant professor in the Department of Laboratory Medicine, Yale School of Medicine, told MEA WorldWide (MEAWW). She adds, “For the flu, there is a safe and effective vaccine, which is the annual flu shot. This is still the best step you can take to avoid getting sick with the flu. An effective strategy against all respiratory viruses is to avoid becoming infected by preventing exposure to germs, with handwashing and other measures such as masks.”
Funded by the National Institutes of Health and the National Institute of General Medical Sciences, the study has been published in The Lancet Microbe. The findings help answer a mystery surrounding the 2009 H1N1 swine flu pandemic: an expected surge in swine flu cases never materialized in Europe during the fall, a period when the common cold becomes widespread. The researchers, however, do not know whether the annual seasonal spread of the common cold virus will have a similar impact on infection rates of those exposed to SARS-CoV-2, the virus that causes Covid-19. “It is impossible to predict how two viruses will interact without doing the research,” says Dr Foxman.
Sore throat and runny nose are usually the first signs of a cold, followed by coughing and sneezing. Most people recover in about 7-10 days. “The symptoms of flu can include fever or feeling feverish/chills, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches and fatigue (tiredness). Cold symptoms are usually milder than the symptoms of flu. People with colds are more likely to have a runny or stuffy nose. Colds generally do not result in serious health problems,” says the US Centers for Disease Control and Prevention (CDC).
To test how the rhinovirus and the influenza virus interact, Dr Foxman’s lab created human airway tissue from stem cells that give rise to epithelial cells, which line the airways of the lung and are a chief target of respiratory viruses. They found that after the tissue had been exposed to rhinovirus, the influenza virus was unable to infect the tissue. The antiviral defenses were already turned on before the flu virus arrived, reveals analysis. The presence of rhinovirus triggered the production of the antiviral agent interferon, which is part of the early immune system response to the invasion of pathogens, explain researchers.
“The Covid-19 pandemic highlights the urgency of understanding and predicting the spread of respiratory viruses, to design effective interventions. SARS-CoV-2 transmission is expected to intersect with the annual autumn rhinovirus epidemic and the winter influenza season in 2020-21. The work presented here raises the question as to whether rhinovirus and other respiratory viruses will interfere with SARS-CoV-2,” writes the team. They explain, “Studies indicate that like influenza A virus (IAV) and many other viruses, SARS-CoV-2 is inhibited by interferons. If interference by rhinovirus disrupted the 2009 IAV epidemic in Europe, viral interference, or even therapeutic induction of the airway interferon response, might have the potential to disrupt the current pandemic. However, more work is needed to establish the effect of rhinovirus and airway interferon responses on SARS-CoV-2.”
Dr Foxman’s lab has begun to study whether the introduction of the cold virus before infection by the Covid-19 virus offers a similar type of protection. “This work provides compelling evidence that rhinovirus infection can protect against subsequent influenza A virus (IAV) infection and supports the idea that interference from rhinovirus delayed the spread of the 2009 IAV pandemic in Europe. These findings indicate that viral interference might shape and potentially interrupt an epidemic, and should be considered when predicting and designing interventions for seasonal influenza epidemics and the ongoing Covid-19 pandemic,” the authors suggest.