Can We ‘Use’ One Virus To Fight off Other Viruses?

An artistic representation of a coronavirus. Image: PIRO4D/pixabay.

Respiratory diseases are on the rise, and scientists are leaving no stone unturned to keep existing and emerging respiratory infections at bay.

In a recent study published in The Lancet Microbe, researchers at Yale University found that prior exposure to rhinoviruses, which cause about a fifth of all common-cold infections, could prevent influenza viruses from setting up an infection in the same body. So they are analysing whether a similar strategy could be used to stave off the SARS-CoV-2 virus – the pathogen behind the ongoing pandemic.

In 1918, Spanish flu, caused by a strain of the influenza virus, killed one-third of the world’s population. In 2009, another strain wreaked havoc with swine flu, and killed over 18,000 people around the world. On August 10, 2010, the WHO declared an end to the 2009 influenza pandemic. However, the virus continues to circulate as a seasonal virus, causing sickness and death every year.

The seasonal flu is characterised by a phenomenon called antigenic drift, where newer strains of the virus emerge continuously, and each strain is slightly different from the one that caused the last season’s infections. As a result, there’s a mismatch between the vaccine strain and the strain that’s currently circulating. This is why getting one vaccine shot doesn’t suffice. We need to periodically revaccinate ourselves against newer strains.

The common cold is caused by different viruses. One of them is the rhinovirus, which causes benign upper respiratory tract infections. Both the seasonal flu and the common cold strike at roughly the same time every year. And during the 2009 H1N1 influenza pandemic, data from several European countries suggested that the rhinovirus infections could have slowed the spread of the influenza virus.

So the scientists at Yale University attempted to determine if the rhinovirus and the influenza virus interacted in any particular way. They examined over 13,700 respiratory samples obtained from patients between 2-16 and 2019. They found that in the months when both the rhinovirus and the influenza virus were active, the influenza virus was absent if the rhinovirus was present.

“When we looked at the data, it became clear that very few people had both viruses at the same time,” Ellen Foxman, an assistant professor of laboratory medicine and immunobiology at the university, told The Independent.

To confirm their findings, the researchers also inoculated both the viruses in cell culture. A cell culture is a clump of cells from multicellular organisms maintained outside the body, in specially designed containers with precisely controlled temperature, humidity and air quality, and on a diet determined by what researchers want to study.

The Yale team selected the cells from the human airway to culture, since both the influenza virus and the rhinovirus target these cells during an infection. They found that in those cultures that had previously been inoculated with the rhinovirus, the influenza virus did not replicate.

“The antiviral defences were already turned on before the flu virus arrived,” Foxman told The Independent. In their paper, the team proposed a mechanism called a viral interference, which prevents the influenza virus from establishing an infection in the presence of the rhinovirus.

That is, viral interference is the phenomenon in which an infection due to one virus temporarily protects the body from an infection by other viruses.

The researchers also write that the initial rhinovirus infection could have led the cells to synthesise antiviral agents called interferons, which then could have mounted the viral interference. Interferons are signalling molecules that ‘talk’ to different cells of the immune system.

An interferon released by one cell alerts other immune cells to fight an invader. So interferons play an important role in stimulating the immune system to establish an antiviral state. Their name comes from the fact that they can interfere with viral replication.

The COVID-19 pandemic has reminded us of the need to understand the spread of respiratory viruses so we can implement the best prevention and control measures we can, and asap. In light of the ongoing pandemic, the Yale research team has started to look into whether deliberate exposure to a rhinovirus could keep the novel coronavirus away.

But irrespective of what the researchers find, we must continue to wear masks, maintain a safe distance from other people (to the extent possible) and maintain good hand hygiene.

Niranjana Rajalakshmi is a veterinary microbiologist.

Scroll To Top