For all intents and purposes, the fight against SARS-CoV-2 in the Brazilian city of Manaus should be won already. By August 2020, three quarters of the population in the capital of the state of Amazonas had already been infected with the novel coronavirus — enough for the area to build up solid herd immunity. But then last December, COVID-cases were suddenly spiking again. Now hospitals in Manaus are running out of oxygen to keep corona-patients alive.

There's a chance that people in the Brazilian city have caught the new P.1. virus variant, which manages to "escape" the immune system's response in some people. Researchers now hope to learn more by sequencing samples from these patients. 

An "immune escape" like this is a serious concern because it could mean that even people who have already recovered from COVID could be infected again, and that the vaccines on the market aren't effective anymore or need refreshing. 

But at least so far, the virus doesn't seem to have become resistant against the vaccines currently being administered to hundreds of thousands of people across the world, vaccinologist Philip Krause, chair of a World Health Organization (WHO) working group on COVID-19 vaccines, said.

"The not-so-good news is that the rapid evolution of these variants suggests that if it is possible for the virus to evolve into a vaccine-resistant phenotype, this may happen sooner than we like," Krause told the journal Science.

The evolution of virus variants

To reproduce, viruses insert their genetic make-up into a host cell. Each reproduction comes with small copying mistakes, and each one of these mistakes in turn changes the virus's genetic code — it mutates.

Vaccines put evolutionary pressure on the virus. The variants of the virus that are selected to continue reproducing are those that manage to evade the immune system by mutating.

That doesn't necessarily mean that a virus becomes more and more deathly through selection. After all, a virus that kills its host can't spread as well and disappears, making room for more harmless variants to spread again.

But new findings from the British government's "New and Emerging Virus Threats Advisory Group" suggest that the variant first discovered in the UK might not just be up to 70 percent more contagious, but perhaps deadlier as well. There's not enough data to prove this yet, though.

The problem with weak vaccines

When weak vaccines are used, however, or the second dose is delayed for too long, the vaccine has the exact opposite of the desired effect. That's what Pennsylvania State University virologist Andrew Read warns against. In 2001, his research with poultry viruses led him to the conclusion that low-efficacy vaccines could even promote the development of more dangerous virus strains.

That's why some experts view delaying the second dose of the vaccine, which the UK is already implementing and the US might soon, critically. Their argument: More people will build up initial protection this way, but they won't be able to develop a sufficiently strong immune response. The body will fight the more dangerous virus strains longer, giving the virus more time to evade death through vaccination. When people who have yet to be vaccinated encounter this type of virus, there could be deathly consequences. 

A large-scale delay of the second dose could create a pool of millions of people who have enough anti-bodies to slow down the virus and not get sick, but not enough to actually eradicate the pathogen. And that could be the perfect recipe for the creation of strains who are vaccine-resistant, Florian Krammer, a virologist at the Icahn School of Medicine at Mount Sinai in New York, told Science.

"If we end up with everybody just getting one dose with no doses available for a timely boost, that would in my opinion, be a problem," Krammer said.

Other experts view the uncontrolled spread of the virus caused by higher contagiousness as the greater risk.

"It's carnage out there," says evolutionary microbiologist Andrew Read of Pennsylvania State University. "Twice as many people with partial immunity has got to be better than full immunity in half of them."

Seasonal updates for the corona vaccine?

Fortunately many vaccines have managed to remain efficient through the normal cycle of virus evolution. Neither smallpox nor measles developed a mutation that evaded the immunity brought about by the vaccines developed to eradicate them.

In the past, only a few viruses have developed to become vaccine-resistant. One exception is the seasonal flu, which changes so quickly that it requires a new vaccine every year.

If SARS-CoV-2 behaves in a similar way, the corona vaccines would have to be updated regularly as well. According to BioNTech-Pfizer, such an update for the mRNA-vaccines could be developed within weeks. But the testing and the authorization, as well as the production and distribution of the vaccine takes time. And people across the world are already waiting for the currently authorized vaccines with bated breath.