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Influenza viruses undergo rapid genetic changes that enable them to evade the human immune system proficiently, preventing antibodies from being produced in response to an infection or vaccination to neutralize new viruses. This is why Influenza vaccines need to be evaluated every year to ensure they remain effective against new influenza viruses. Mutations within SARS-CoV-2 have already produced several variants, some of which (such as the South African variant) partially evade the body's immune response. As a result, some vaccine manufacturers have already started to develop new versions of their vaccines.

In a study published in Virus Evolution, researchers from Charité–Universitätsmedizin Berlin compared the evolution of prevalent common cold coronaviruses with that of influenza viruses. The Charité virologists studied the genetic evolution of four well-known harmless cold coronaviruses responsible for approximately 10 percent of common colds. Like SARS-CoV-2, they enter human cells using a 'spike protein,' a surface protein that gives the virus its characteristic crown-like appearance (and name) and is the target of all current COVID-19 vaccines.

The researchers focused on the two longest-known coronaviruses (termed 229E and OC43), tracing changes in the spike gene approximately 40 years into the past. Based on the mutations that occurred over time, they produced phylogenetic trees for both coronaviruses and compared them with the phylogenetic tree of H3N2, an influenza subtype that is particularly effective at evading the human immune response.

The scientists' calculations revealed one common feature: all three viruses had a pronounced, ladder-like shape. They explained that "an asymmetrical tree of this kind likely results from the repeated replacement of one circulating virus variant by another which carried a fitness advantage." In addition, this is evidence of 'antigenic drift,' which is a process involving changes in the surface structure, which enable viruses to evade the human immune response. These findings show that these common coronaviruses also evade the immune system, just like the influenza virus.

However, another important factor that should be considered is the speed at which this evolutionary adaptation happens. While the influenza virus accumulated 25 mutations per 10,000 nucleotides per year, the common cold coronaviruses accumulated approximately six such mutations in the same time frame, a rate of change four times slower than that of the influenza virus.  SARS-CoV-2 is currently estimated to change at a rate of approximately ten mutations per 10,000 nucleotides per year, meaning the speed at which it evolves is substantially higher than that of common coronaviruses. Based on the rates of evolution seen in common cold coronaviruses, it is expected that SARS-CoV-2 will start to change more slowly once infections begin to decrease, meaning once a large proportion of the global population has developed immunity either as a result of infection or through vaccination. Therefore, it is expected that COVID-19 vaccines will need to be monitored regularly throughout the pandemic and updated where necessary. Once the situation has stabilized, vaccines are likely to remain effective for longer.

References:

1. Wendy K Jo, Christian Drosten, Jan Felix Drexler. The evolutionary dynamics of endemic human coronaviruses. Virus Evolution, 2021; 7 (1) DOI: 10.1093/ve/veab020
   
2. Charité - Universitätsmedizin Berlin. "Will COVID-19 vaccines need to be adapted regularly?." ScienceDaily. ScienceDaily, 25 March 2021. https://www.sciencedaily.com/releases/2021/03/210325115420.htm

Michele Cherfane, PhD
Associate Professor of Public Health
College of Health Sciences
Abu Dhabi University