Medicinal

Opinion | We are studying the evolution of viruses. We think that the coronavirus is happening.

Sarah Coby, Jesse Bloom, Tyler Star, Nathaniel Rush

Dr. Cobey is studying the interactions of immunity, viral evolution, and transmission at the University of Chicago. Dr. Bloom and Dr. Starr are studying viral evolution at the Fred Hutchinson Cancer Research Center in Seattle. Lash is Opinion’s graphic editor.

As scientists studying how the virus evolves, we are often asked about the future of the coronavirus. Will it disappear? Will it get worse? Will it disappear into the background of our lives?

Here’s what we know: The omicron variant of the virus was much more infectious and resistant to the vaccine than the original strain that first appeared in Wuhan, China. There is no reason why the virus will not continue to evolve, at least biologically. Coronavirus Mutants that have emerged so far sample only a small portion of the gene space that is most likely to be available for evolutionary exploration.

Viruses like SARS-CoV-2 face one of the highest priority pressures to improve spread. Viruses that cause more infections are more successful. The virus becomes more contagious and can do this by evading the immune system. This coronavirus has several indications that make it better spread to humans.

However, many scientists, including us, expected SARS-CoV-2 to be exposed to evolutionary pressure for better infection, but note how well the virus responded to that pressure. Deserves. Recent variants such as Omicron and Delta were the first strains to spread worldwide in early 2020. This is a significant increase, and SARS-CoV-2 is more contagious than many other human respiratory viruses. These big jumps of infectivity have so far played a major role in driving a pandemic.


Graph showing the characteristics of a specific SARS-CoV-2 mutant. Along the X-axis, a decrease in the effectiveness of the antibody against the mutant has been shown. Along the Y-axis, it shows how infectious the mutant is compared to the original SARS-CoV-2.





How the coronavirus changed

Compare coronavirus variants with early 2020 strains.

Antibodies

Low effect

Estimated decrease in antibody efficacy

How the coronavirus mutated

Compare coronavirus variants with early 2020 strains.

Antibodies

Low effect

Estimated decrease in antibody efficacy

How the coronavirus changed

Compare coronavirus variants with early 2020 strains.

Antibodies

Low effect

Estimated decrease in antibody efficacy


Source: Infectivity is based on Marlin Figgins and Trevor Bedford’s estimation of growth dominance. Antibody escape is based on antibody sera collected from patients treated with the Moderna vaccine.

Note: The numbers are approximate. The Omicron numbers reflect the BA.1 lineage of the variant and are estimated based on the discovery of the 105% growth benefit of Omicron compared to Delta.

How contagious SARS-CoV-2 is is an open issue, but it has its limits. Even evolution is constrained. Cheetahs cannot evolve infinitely fast, and SARS-CoV-2 cannot be transmitted indefinitely.

Diffusing capacity of other viruses has peaked. Some respiratory viruses, such as measles, are more contagious than today’s SARS-CoV-2. Other viruses, such as influenza, are generally less contagious than SARS-CoV-2. We know when this coronavirus reaches the infectious plateau, but it does happen in the end.

Such viruses may also spread better by “escaping” immunity to previous variants. In the early days of the pandemic, few had immunity to SARS-CoV-2. But now much of the world has antibodies from vaccinations or previous infections. Antibodies can block infections, and mutants with mutations that surround them become increasingly advantageous.

The importance of antigenic escape became apparent at Omicron. Earlier variants like Delta were able to evade the antibody slightly, but Omicron has many mutations that reduce the ability of the antibody to recognize it. This, coupled with the infectivity of Omicron, made it possible. To cause a huge wave of infection.

The fact that the virus developed the ability to infect vaccinated or previously infected people was not surprising, but it was certain how it happened in Omicron.Evolution often progresses Step by step, With a new successful variant derived from the recently successful one. That’s why 6 months ago. Many scientists, We thought that the following variants, including us, would derive from the then dominant Delta, but evolution was contrary to our expectations, with a huge number of mutations and was derived from Delta. Got no Omicron. I don’t know exactly. Many scientists (including us) suspect that the mutant emerged from someone who couldn’t get rid of the virus well, but how the virus made a major evolutionary jump leading to Omicron. Is it?

It is impossible to say whether future variants will make larger Omicron-like jumps or result in more typical gradual changes, but SARS-CoV-2 has evolved to escape immunity. I’m sure I will continue.

The infectivity of the virus will level off at some point, but other human viruses that escape immunity will continue to do so. Influenza vaccines have been updated annually for decades to track the evolution of the virus, and some influenza viruses show no signs of slowing down. Antigenic escape has endless evolutionary weapons competition because the immune system can constantly make new antibodies and the virus has a huge number of mutations to search accordingly. For example, Omicron has only a few of the many mutations observed in SARS-CoV-. 2 or related bat virus. This is just a small part of the lab experiments that suggest that the virus may be potentially searchable.

Taken together, SARS-CoV-2 is expected to continue to cause new epidemics, but will be increasingly driven by its ability to evade the immune system. In this sense, the future may look like seasonal flu. New variants cause a wave of cases each year. If this happens, the vaccine should be updated regularly, similar to the influenza vaccine, unless a broader variant-resistant vaccine is developed.

And, of course, how important all of this is to public health depends on how sick the virus is. This is the most difficult prediction, as evolution chooses a virus that spreads well and most of the time it increases or decreases the severity of the disease. It’s a matter of luck, but it’s known that immunity reduces the severity of the disease, even if it doesn’t completely block and spread the infection. Immunity obtained from vaccination and previous infections has helped mitigate the effects of Omicron waves in many countries. Vaccines and other measures that delay renewal or improvement infections continue to be the best strategy to address the uncertain future of evolution.

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