July 22, 2021 – A year ago, scientists who envisioned the future of the COVID-19 pandemic were feeling optimistic. The development of vaccines was heading towards unprecedented achievements. And unlike the viruses that cause influenza or AIDS, they believed, this virus could not mutate to escape the fully primed human immune system.
“Fortunately, SARS-CoV-2 does not appear to have devised such tricks yet – suggesting that we still have an opportunity to stem its spread and the pandemic by pursuing a relatively simple vaccine approach,” wrote two immunologists at Yale University in July. 31, 2020, test for The New York Times.
That was the time.
Since then, the UK, South Africa, India and Brazil have all discovered “variants of concern” – mutant strains that spread more easily and can cause more serious disease.
The new kid on the block, the Delta variant first detected in India, appears to be much more contagious than its original cousin. It is quickly becoming the dominant source of new COVID-19 cases everywhere, causing the number of new cases to spike even when a large percentage of the population has been vaccinated.
At the same time, the effort to vaccinate the whole world is running up against such great barriers that hope of extinguishing the virus in this way quickly fizzled out.
“I think there is a broad consensus that the virus will not go away,” said Amalio Telenti, MD, chief data scientist at San Francisco-based company Vir Biotechnology..
Vaccines are a major barrier to the virus
This does not mean that the death toll from COVID-19 will continue to rise indefinitely, or even to peak last winter. The virus has yet to develop the ability to completely evade the immune response stimulated by the best of current vaccines.
“What we have seen with the data is that – at least with mRNA vaccines (Pfizer and Moderna) – they offer great efficacy against the Delta variant,” said Ravina Kullar, PharmD, infectious disease specialist. and epidemiologist at UCLA..
But it does mean that humanity faces a fight that could expand for the foreseeable future.
Early on, epidemiologists spoke of “herd immunity,” the condition in which enough people are vaccinated that a virus cannot find enough new hosts to continue to replicate. This can happen naturally if enough people are infected or get vaccinated.
At the start of the pandemic, a handful of scientists argued that allowing widespread infection was the fastest option for containing the virus through natural immunity. This approach was quickly criticized as epidemiologists calculated the millions of deaths that would result.
And there is no guarantee that natural immunity can eliminate a virus. Often a virus evolves to evade the immune response, reinfecting more people until it develops new immunity. This results in waves of contagion that come and go over time, as is the case with the flu.
Vaccination offers a slower but much safer approach to crushing a virus. It happened with smallpox, eradicated from the world in 1980 after decades of global vaccination efforts. In addition, vaccination may be more effective than natural immunity. This appears to be the case with this coronavirus.
It comes down to math
But so far mankind has not been able to eradicate viruses other than smallpox by vaccination. The success of such an effort depends 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 math problem. On average, all people infected with the original coronavirus that appeared in Wuhan, China, have infected another 2.5 people. Epidemiologists have calculated that by vaccinating 70% of the population, it could fall to less than one new infected person, leading to a decrease in the virus.
People infected with the Delta variant, on the other hand, seem to infect more people – estimates range from 3.5 to seven new infections. This raises the bar for collective immunity up to 85% of the population.
Immunization efforts at the moment do not appear likely to reach this level. In many countries where vaccines are widely available, the rate of new vaccinations has plummeted, delaying them to even reach the original target of 70%.
At the current rate, the United States will not reach this target until December. But 11% to 14% of Americans say they don’t want to be vaccinated if given a choice. Add that to the 10% who want to “wait and see”, and collective immunity in the United States seems out of reach.
In some low-income countries, the prospect of herd immunity seems even more remote: to date, only around 1% of their population has been vaccinated.
So why did scientists think herd immunity was possible? The first images of coronavirus suggested a virus that would only evolve slowly.
Coronaviruses have the ability to re-read their genetic material when they replicate. This makes mutations less likely than with many other viruses. And the virus was under little evolutionary pressure as it had a lot of new victims without immunity.
But as the virus spreads, meets more and more people and more and more immune responses, mutations become more likely. “If you put it in hundreds of millions of people, other variations are going to happen,” said John P. Moore, PhD, professor of microbiology and immunology at Weill Cornell Medicine in New York City..
Some scientists believe that the virus will never be able to change enough to completely evade the immunity generated by the vaccine. These vaccines stimulate antibodies that attack parts of the spike that the virus uses to attach itself to its host’s cells. In the more contagious variants, including Delta, the virus has altered parts of its peak, making it less susceptible to antibodies.
Vaccines always stimulate antibodies that attack other parts of the tip, so their effectiveness is always strong. In addition, vaccines stimulate cellular immunity, a process by which immune cells destroy infected cells before they can release viruses.
There is growing evidence that this natural immune process works against variants, says Pauline Vetter, MD, infectious disease specialist at Geneva University Hospitals in Switzerland.
Additional doses of vaccine, booster shots with improved formulas and even brand new types of vaccines are all being researched.
Is a finish line in sight?
Could the virus end up in an evolutionary dead end?
“You can’t mutate spike proteins indefinitely without them losing some of their function,” Moore said. “They’re not infinitely plastic. And yet, you can imagine that there are variations 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 survey of 119 immunologists by Nature, 89% said they expected the virus to become endemic, “a virus that continues to circulate in pockets of the world’s population.”
That way it could look like the flu, perhaps increasing and decreasing with the seasons, worse one year, better another year as the virus and the defenses against it evolve.
Some parts of the world could approach herd immunity through vaccination. In the United States, that could mean entire states, or maybe cities. “We’re not going to have national herd immunity, but we’re probably close to herd immunity in important parts of the country,” Moore said. “I live in Manhattan. Life is pretty normal.”
In Los Angeles, meanwhile, Kullar warns that the death rate is on the rise again and that local health officials are demanding that even those vaccinated wear their masks in public places.
“I think we just have to keep in mind that the pandemic is not over yet,” she said.