Covid-19: How will delta variant evolve? Here's what the theory tells us

 Delta is not the end of the story for SARS-CoV-2, the virus that causes Covid-19. Here's what evolutionary theory tells us happens next

The COVID-19 pandemic is a dramatic demonstration of evolution in action. Evolutionary theory explains much of what has already happened, predicts what will happen in the future, and suggests which management strategies are likely to be the most effective.

For instance, evolution explains why the Delta variant spreads faster than the original Wuhan strain. It explains what we might see with future variants. And it suggests how we might step up public health measures to respond.

But Delta is not the end of the story for SARS-CoV-2, the virus that causes COVID-19. Here’s what evolutionary theory tells us happens next.

Remind me again, how do viruses evolve?
Evolution is a result of random mutations (or errors) in the viral genome when it replicates. A few of these random mutations will be good for the virus, conferring some advantage. Copies of these advantageous genes are more likely to survive into the next generation, via the process of natural selection.

New viral strains can also develop via recombination when viruses acquire genes from other viruses or even from their hosts.

Generally speaking, we can expect evolution to favor virus strains that result in a steeper epidemic curve, producing more cases more quickly, leading to two predictions.

First, the virus should become more transmissible. One infected person will be likely to infect more people; future versions of the virus will have a higher reproductive or R number.

Second, we can also expect evolution will shorten the time it takes between someone becoming infected and infecting others (a shorter “serial interval”).