US Pharm. 2021;46(4):1.

In a study published in Virus Evolution, researchers from Charité–Universitätsmedizin Berlin compared the evolution of endemic common cold coronaviruses with that of influenza viruses. While the pandemic is ongoing, the scientists predict, vaccines will need to undergo updates. A few years into the postpandemic period, however, vaccines are likely to remain effective for longer, they add.

Influenza viruses adeptly evade the human immune system, undergoing such rapid changes that antibodies produced by the immune system in response to a previous infection or vaccination become unable to neutralize them. This is why the complex task of evaluating and updating the seasonal influenza vaccine has to be repeated every year. Mutations within SARS-CoV-2 have already produced a number of variants. As a result, some vaccine manufacturers have already started to develop new versions of their vaccines. What does this mean for the future?

The Charité virologists studied the genetic evolution of the four currently known cold coronaviruses. These relatively harmless coronaviruses are responsible for approximately 10% of common colds and have been circulating in humans significantly longer than SARS-CoV-2. Like SARS-CoV-2, they enter human cells using “spike protein,” a surface protein that gives the virus its characteristic crown-like appearance and is the target of all current COVID-19 vaccines.

The researchers focused on the two longest-known coronaviruses, tracing changes in the spike gene. Based on the mutations that emerged, they produced phylogenetic trees for both coronaviruses. The researchers compared their findings with the phylogenetic tree of H3N2, an influenza subtype that is particularly adept at evading the human immune response.

The scientists’ calculations revealed that all three viruses had a pronounced, ladder-like shape. “An asymmetrical tree of this kind likely results from the repeated replacement of one circulating virus variant by another which carried a fitness advantage,” explained the study’s first author, Dr. Wendy K. Jó from Charité’s Institute of Virology. “This is evidence of ‘antigenic drift,’ a process involving surface structure changes that enable viruses to evade the human immune response. It means that these endemic coronaviruses also evade the immune system, just like the influenza virus.”

Next, the researchers determined the three viruses’ evolutionary rates. While the influenza virus accumulated 25 mutations per 10,000 nucleotides per year, the coronaviruses accumulated approximately six such mutations in the same time frame. The rate of change of the endemic coronaviruses was therefore four times slower than that of the influenza virus. SARS-CoV-2 is currently estimated to change at a rate of approximately 10 mutations per 10,000 nucleotides per year, meaning the speed at which it evolves is substantially higher than that of the endemic coronaviruses.

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