The COVID-19 pandemic shows evolution at work. Evolutionary theory can explain many of the events that have occurred, and it predicts the future. It also suggests the best management strategies.
Evolution explains, for example, why the Delta strain spreads faster than its original Wuhan counterpart. This explains the future possibilities for variants. It also suggests ways we could increase public health responses.
SARS-CoV-2 is the virus that causes COVID-19, and Delta isn't the end of the story. Here's what evolutionary theory says will happen next.
Remember me, how does a virus evolve?
When the viral genome replicates, evolution is caused by random mutations or errors. Some of these random mutations can be beneficial for the virus and confer some advantage. Natural selection makes it more likely that copies of these beneficial genes will survive to the next generation.
Recombination is also a method by which viruses can acquire genes from other viruses, or from their hosts.
We can generally expect evolution to favor viruses that produce more cases quickly and have a steeper epidemic curve.
The virus should be more easily transmissible. A single infected person is likely to infect many others; future versions will have a higher reproductive number or R number.
We can also expect that evolution will reduce the time between infecting someone and infecting them (a shorter "serial interval")
These predicted changes are good news for the virus but not for the host.
Aha! That explains Delta
This theory explains why Delta has taken over the world, replacing the original Wuhan.
While the original Wuhan strain had a R value of 2-3, Delta's R value for Delta is around 5-6 (some researchers claim this number is even higher). Infected with Delta, a person is more likely to infect two times as many people than the original Wuhan strain.
Evidence also suggests that Delta has a shorter serial interval than the original Wuhan strain.
This could be due to a higher viral load, or more copies of the virus in an infected person with Delta than with previous strains. This could allow Delta to transmit earlier after infection.
Delta may transmit more easily after "fleeting contact" and in open air if there is a higher viral load.
How do vaccines impact the evolution of the virus?
COVID-19 vaccines, which were designed to protect against the original Wuhan strain, work against Delta but are less efficient. Evolutionary theory predicts that viral variants capable of evading vaccines will have an evolutionary advantage.
We can expect a race between vaccine makers and virus developers, as vaccines try to catch up to viral evolution. We will likely see regular booster shots to combat these new variants. This is similar to flu booster shots.
The COVID-19 vaccine reduces your chances of passing the virus on to others but doesn't completely block transmission. Evolutionary theory offers us a warning.
With most disease-causing microorganisms, there is a tradeoff between transmittibility and severity of illness (virulence). To transmit, you must have a certain viral load.
We can expect a shift towards higher virulence if vaccines fail to block transmission if they are not 100% effective. The theory predicts that the virus will eventually spread from unvaccinated individuals, which is a side effect of being transmissible.
What about future versions?
It's very likely that the virus will evolve in the near future.
Its R value will increase, meaning that more people will become infected within a single generation.
The serial interval will decrease, and people will be more infectious.
Variants can make vaccines less efficient (vaccine evasion).
We don't know how fast or how far these changes will go.
Scientists believe the virus could be nearing "peak fitness". However, scientists believe it still has some tricks up its sleeves.
The UK's Scientific Advisory Group for Emergencies has been looking at scenarios for the long-term evolution and spread of the virus.
According to it, "antigenic drift" is almost certain. This is an accumulation of small mutations that will cause the effectiveness of current vaccines to decrease. Boosters with modified vaccines are therefore essential.
The virus could undergo more drastic changes ("antigenic shift") due to recombination with human coronaviruses. This is considered a realistic possibility. This would require more extensive re-engineering.
SAGE believes there is a real possibility of a reverse zoonosis, which could lead to a virus more dangerous (harmful) for humans or that can evade vaccines. SARS-CoV-2 could infect animals before it crosses over into humans. SARS-CoV-2 has already infected rodents, cats, and mink.
Spread of COVID in minks could hamper potential vaccine, warns #EU disease centre The spread of COVID variants via mink farms could compromise the efficacy of a vaccine, according to a rapid risk assessment published by the European Centre for ... https://t.co/ftTq78hisK #Europe pic.twitter.com/9cpjykFTCI EUwatch (@EUwatchers) November 12, 2020
Is the virus likely to become more dangerous?
The virus versions that cause severe illness in their hosts (highly virulent) are usually rejected. This is because the virus could cause people to become more sick, or even die, which reduces the risk of it spreading to others.
SAGE believes that this process will not cause the virus's virilization to decrease in the short-term, but it is possible in the long-term. SAGE believes that recombination, which is what other coronaviruses do, could lead to more dangerous strains.
The critical question is: Do we know if the virus will get more deadly? However, we cannot expect the virus will magically disappear.
Will humanity catch up?
Unfortunately, the answer to this question is "no". Unfortunately, humans are not fast enough to reproduce and accumulate enough positive mutations quickly enough to keep up with the virus.
It also doesn't kill the majority of people it infects. It doesn't even kill most people over the age of 18. There is no "selection pressure" on humans to become more favorable to the virus.
What about future pandemics, however?
Evolutionary theory also warns of future pandemics.
Strongly selected for: A gene mutation that allows a virus from a rare and obscure species (like a bat), to access the most widespread and widely distributed large animal species on the planet, humans.
We can also expect future pandemics if animal viruses spread to humans as they did in the past.
Hamish McCallum is Director, Centre for Planetary Health and Food Security at Griffith University, Griffith University.
This article was republished by The Conversation under Creative Commons. You can read the original article.
