July 22, 2021 – A year ago scientists were optimistic when looking at the future of the COVID-19 pandemic. Vaccine development was nearing an unprecedented level. And unlike the viruses that cause flu or AIDS, they thought this virus couldn’t mutate to evade the fully prepared human immune system.
“Thankfully, SARS-CoV-2 doesn’t seem to have developed such tricks yet – suggesting that we still have the ability to contain its spread and the pandemic by taking a relatively straightforward vaccine approach,” wrote two Yale immunologists University in a July 31st, 2020 article for the New York Times.
Those were the days.
The Delta variant of Covid-19 is “one of the most contagious respiratory viruses that we know and that I have seen in my 20-year career”.
– @CDCDirector
– Alexis Benveniste (@apbenven) July 22, 2021
Since then, the UK, South Africa, India and Brazil have discovered “worrying variants” – mutant strains that can spread more easily and cause more serious diseases.
The new kid on the block, the Delta variant first discovered in India, seems far more contagious than its original cousin. It is fast becoming the dominant source of new COVID-19 cases everywhere and leading to a surge in new cases even when a large percentage of the population has been vaccinated.
At the same time, efforts to vaccinate the whole world are encountering such significant barriers that hope of wiping the virus out in this way quickly faded.
“I think there is broad consensus that the virus will not go away,” said Amalio Telenti, MD, chief data scientist at San Francisco-based Vir Biotechnology.
Vaccines are a high barrier to viruses
That doesn’t mean the death toll from COVID-19 will continue to rise indefinitely or even hit last winter’s highs. The virus has not yet developed the ability to completely escape the immune response stimulated by the best current vaccines.
“What we have seen with the data is that they – at least with the mRNA vaccines (Pfizer and Moderna) – offer great effectiveness against the Delta variant,” says Ravina Kullar, PharmD, specialist in infectious diseases and epidemiologist at the UCLA.
But it does mean that humanity is facing a struggle that could drag on for the foreseeable future.
The more uncontrolled the spread, the greater the risk for even more dangerous variants. Vaccination, masks, ventilation, and distancing can stop Covid, including Delta. Variants remain the wild card for the course of the pandemic. Delta may not be the worst strain the virus has put on us. 19 /
– Dr. Tom Frieden (@DrTomFrieden) July 21, 2021
From the beginning, epidemiologists spoke of “herd immunity,” the condition in which enough people are vaccinated that a virus cannot find enough new hosts to continue to reproduce. This can of course happen if enough people become infected or get vaccinated.
At the beginning of the pandemic, a handful of scientists argued that widespread infection was the fastest way to contain the virus through natural immunity. This approach was quickly criticized when epidemiologists calculated the millions of deaths that would result from it.
And there is no guarantee that natural immunity can turn a virus off. Often times, a virus will evolve to bypass the immune response and re-infect more people until it develops a new immunity. This leads to waves of contagion that go up and down over time, as is the case with the flu.
Vaccination offers a slower, but much safer, approach to crushing a virus. That happened with smallpox, which was eradicated worldwide in 1980 after decades of global vaccination efforts. In addition, vaccination can be more effective than natural immunity. That seems to be the case with this coronavirus.
It depends on math
But so far mankind has not succeeded in eradicating viruses other than smallpox with vaccinations. The success of such an effort will depend on several factors, including the effectiveness of the vaccine and other health measures such as – in the case of the coronavirus – social distancing and masking.
The race between the evolution of the virus and the vaccination of humans boils down to a mathematical problem. On average, anyone who contracted the original coronavirus that showed up in Wuhan, China infected 2.5 more people. Epidemiologists calculated that vaccinating 70% of the population could drop the numbers to fewer than one new infected person, which could cause the virus to wane.
People infected with the Delta variant, on the other hand, seem to infect more people – estimates range from 3.5 to seven new infections. The benchmark for herd immunity is up to 85% of the population.
At the moment, vaccination efforts do not seem to be reaching this level. In many countries where vaccines are widespread, the number of new vaccinations has fallen, even reaching the original target of 70%.
As things stand at present, the US will not achieve this goal until December. But 11% to 14% of Americans say they don’t want to get vaccinated when given a choice. Add that to the 10% who want to “wait and see,” and herd immunity seems to be out of reach in the US.
@scdhec announced 714 more cases of COVID-19 today and a percentage positive of 8.8%. The increase is likely influenced by the Delta variant and the lower vaccination rate in our state. We can really do something about it. We can get vaccinated! pic.twitter.com/UxcKIJAgpt
– Aditi Srivastava Scheffel, PhD, MPH (@aditisrivastav) July 21, 2021
In some low-income countries, the prospect of herd immunity looks even less likely: only about 1% of their population has been vaccinated.
So why did scientists think herd immunity was ever possible? The first images of the coronavirus indicated a virus that would be slow to develop.
Coronaviruses have the ability to proofread their genetic material as it replicates. This makes mutations less likely than with many other viruses. And the virus was under little evolutionary pressure because it had many new victims with no immunity.
But as the virus spreads, hits more and more people, and hits more and more immune responses, mutations become more likely. “If you subject it to hundreds of millions of people, there will be more variations,” says John P. Moore, PhD, professor of microbiology and immunology at Weill Cornell Medicine in New York City.
Some scientists believe the virus can never change enough to completely escape the immunity created by the vaccine. These vaccines stimulate antibodies that attack parts of the spine that the virus uses to cling to its host’s cells. In the most contagious variants, including Delta, the virus has altered parts of its tip, making it less susceptible to the antibodies.
The vaccines are still stimulating antibodies that attack other parts of the sting, so their effectiveness is still strong. The vaccines also stimulate cellular immunity, a process by which immune cells destroy infected cells before they can release viruses.
There is increasing evidence that this natural immune process works against the variants, says Pauline Vetter, MD, specialist in infectious diseases at Geneva University Hospital in Switzerland.
Additional doses of vaccine, booster vaccinations with improved formulas, and even entirely new types of vaccines are being explored.
Is there a finish line in sight?
Could the virus hit an evolutionary dead end?
“You can’t mutate the spike proteins indefinitely without losing some function,” said Moore. “They are not infinitely plastic. And yet one could imagine that there are some variants that could be worse.”
The complex interplay of these and other factors – such as the durability of the immune response – makes it difficult to predict the future of the pandemic.
But most experts believe it won’t go away. In a Nature survey of 119 immunologists, 89% said they expect the virus to become endemic, “one that continues to circulate in parts of the world’s population”.
That way, it could resemble a flu, perhaps widening and waning with the seasons, worse one year, better another year, as both the virus and the immune system develop against it.
Parts of the world could approach herd immunity through vaccination. In the US, that could mean entire states or maybe cities. “We won’t have national herd immunity, but we are likely to be close to herd immunity in key regions of the country,” said Moore. “I live in Manhattan. Life is pretty normal.”
Meanwhile, in Los Angeles, Kullar warns that the death rate is rising again, and local health officials are even requiring vaccinated people to wear their masks in public places.
“I think we just have to remember that the pandemic is not over yet,” she said.
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