3 Ways To End A Virus

The Clash of the Variants: Alpha vs. Delta

As we entered spring 2021, the Alpha variant of the coronavirus had become the dominant variant worldwide. However, the emergence of the Delta variant, a more transmissible strain, was on the horizon. The question arose: what happens when two variants clash?

Let’s consider a hypothetical scenario where both variants reach an isolated city of 1 million people, all susceptible to both viruses, on the same day. When a person is infected with Alpha, they transmit it to an average of 5 close contacts, then begin to feel sick and immediately isolate themselves. The same process occurs with Delta, except that an infected person transmits it to an average of 7.5 close contacts.

After six days, Alpha will have infected 15,625 people. In contrast, Delta will have infected more than 10 times as many. Just 20 hours later, Delta will have infected the rest of the population, all before Alpha could infect 6% of it. With no one left to infect, Alpha dies out. This model, while drastically simplified, accurately reflects the real-life scenario where Delta drove Alpha toward extinction in a matter of weeks.

How Viruses Can Go Extinct

Viruses are wildly successful organisms. There are about 100 million times as many virus particles on Earth as there are stars in the observable universe. Even so, viruses can and do go extinct. There are three main ways that this can happen.

Firstly, a virus could run out of hosts. This might have happened in early 2020 to a flu lineage known as B/Yamagata. When much of the world shut down, social distanced, and wore masks to slow the spread of COVID-19, that dramatically reduced the number of hosts available for B/Yamagata to infect.

Secondly, a virus could go extinct if it kills all its hosts. This almost happened back in 1950s Australia when scientists released a virus called myxoma to control the population of the invasive European rabbit. The virus evolved to be less deadly, allowing both the virus and the rabbit population to survive.

The third way a virus can go extinct is if it’s outcompeted by another virus or strain, like we saw earlier with Delta and Alpha. However, viruses don’t always compete with each other. A viral species can carve out its own distinct niche, allowing multiple viruses to co-exist.

Will SARS-CoV-2 Ever Go Extinct?

So, will SARS-CoV-2—the species of virus that causes COVID-19—ever go extinct? Variants within the species will continue to arise. Those variants might drive prior ones to extinction, or not. Regardless of how the variants compete, the species itself is pretty firmly established among humans.

If we managed to vaccinate enough people, could we drive SARS-CoV-2 to extinction? Our vaccination campaign against smallpox worked because the vaccine was highly protective against infection and smallpox had no close animal reservoir in which it could hide. But SARS-CoV-2 can hide out in animals, and our current vaccines, while they provide excellent protection against severe illness and death, don’t prevent all infections.

So, conceivably there are two ways that SARS-CoV-2—the entire species—could go extinct: a cataclysmic disaster could kill us all, or we could invent a universal vaccine that prevents all SARS-CoV-2 infections, those caused by all the variants that currently exist and those that don’t. Let’s work toward that second option.