COVID’s evolution may have been driven by human behavior, say biologists

Human behavior may have influenced the evolution of new strains of COVID-19, new AI models suggest.

Vaccination and immune pressures from previous infections are known to cause the emergence of new strains of virus, evolved to bypass our existing immunity. But research from Nagoya University in Japan suggests that our own behavior may have also directed this evolution.

Just like any other organism, viruses evolve over time. Those with survival advantages—like an ability to evade existing immunity—become the dominant strain in the gene pool. One evolutionary trade-off that viruses must consider is the concept of viral load.

Viral load refers to the amount of virus present in each milliliter of body fluid in an infected individual. A higher viral load means that the virus will be more easily transmitted to others. However, if the viral load gets too high, individuals may become too sick to transmit the infection. Therefore, the virus needs to find a perfect middle ground that allows then to be effectively transmitted without killing their host.

So how did SARS-CoV-2 navigate this evolutionary trade off?

In their recent study, published in the journal Nature Communications, the team from Nagoya University found that the SARS-CoV-2 variants that had been most successful at spreading had an earlier and higher peak in their viral load, with a shorter duration of infection. They also developed more quickly inside their host (us) and resulted in an increased proportion of asymptomatic infections.

What does this mean?

The team, led by Shingo Iwami, suggests that these evolutionary changes became advantageous to the virus as a result of human behaviors designed to limit transmission. Once we became aware that we were sick—usually after symptoms began to show—most of us would self-isolate for the recommended time period. Of course, self-isolation prevents the virus from spreading (other than to our unfortunate family members and house mates.) Therefore, if the virus were able to evolve to become more infectious at the start of the infection—i.e. before we realized we were sick—it would have a better chance at spreading.

Moreover, if it was able to evade detection by its host—i.e. produce no symptoms—the host might never know that they were infected, and freely go about their day spreading the virus.

“Our study found that human behavior can also contribute to the virus’s evolution in a more complicated manner, suggesting the need to reevaluate virus evolution,” Iwami said in a statement.

The team hope that their findings will speed up the establishment of new testing regimes, effective screening and isolation strategies moving forward.