Does the Corona virus settle into a certain pattern?

  1. Moon-Kate LoweInternational Features Editor

  1. BMJ
  1. mlooi {at} bmj.com

SARS-CoV-2 is here to stay, with a growing set of questions about science and medicine. In the first part of a new series on unanswered Covid questions, BMJ He asks about our current understanding of waves and variables – and what they might mean for “living with the virus”

“We are seeing a steady [peaks in case numbers] Between waves of infection, the settling point of those plateaus is slightly higher each time, as the virus mutates.

“What we are seeing at the moment is basically the evolution of this virus in real time. We are seeing these waves of infection with different variants that have outperformed their predecessors.”

Are there regional patterns?

Some countries, such as New Zealand and Japan, saw very sharp increases followed by sharp decreases, compared to other countries. These countries have kept relatively low numbers of infections thanks to a combination of strong policies, such as border closures, and significant public adherence to the measures for more than a year before restrictions were relaxed.

What matters for those countries is not the transmissibility of the new variants per se, says Joël Mossong, an epidemiologist at the Luxembourg Health Directorate, but rather the immune status of the population.

“The reason they’re so popular is because they can really find people who haven’t been infected yet or have been infected for a long time,” he explains. “And they are able to evade or evade pre-existing immunity, either from a vaccine or from a previous infection, which was based on a previous variant.” All current COVID-19 vaccines are based on the original “wild-type” strain.

Will these patterns continue?

“As long as these variants continue to be selected for increased transmissibility and immune evasion, especially current vaccine protection, we will continue to see this kind of pattern around the world. But it depends on the variables and where you are,” Young says.

We can expect the wave pattern to continue over the next few years, he adds, unless we become more proactive about mitigating or adapting our vaccines.

Musong says, “It seems that there is [new] Variants sweep every three months. . . But it also seems that each successive wave will be smaller. It really seems to me that the virus wipes out any pockets of susceptibility that are still in the population.”

There’s a lot of immunity in the population now, he says, since most people have been vaccinated, but also from “natural” exposure to the virus, since most people have also been infected previously. “Infectious diseases are a lot like wildfires,” he says. “People are like trees that haven’t been burned yet.”

What happened to the previous variants – and can they go back?

“Old variants are still being discovered in small numbers but likely will not become dominant, as the majority of the world is now being vaccinated with effective vaccines against those,” explains Sakuraba.

with the supremacy of the omicron family (picture 2), it is unlikely that any previously dominant variant will be able to re-enter the loop. Mossong says any previous form would struggle to re-dominate or even gain a foothold. “It’s vaccines, really, that have killed them,” he says. That had already established a great immunity against them. I think it’s unlikely that one of those will come back.”

picture 2

Share of SARS-CoV-2 sequences that are an omicron variant (dark shaded areas), 15 August 2022

Credit: Our World in Data

“Alpha and beta variants weren’t really contagious – although they seemed like a lot of contagion at the time – compared to how easily Omicron, and Delta before it, spread,” says Eleanor Riley, professor of immunology and infectious diseases at the University of Edinburgh, UK, in hindsight. . At that time there were no vaccines or weak immunity.

“In order to go back and grab the omicron, it has to be completely different immunologically,” she says BMJ. “And I’m not sure that would be enough, immunologically, to counter the fact that they are actually not contagious compared to the two up front.”

One exception might be people who are immunocompromised or immunosuppressed, who can have multiple infections from different variants or substrains, Young and Musong say. This could be an evolutionary opportunity for a gene swap – for example, there were concerns in the media about the “deltachron” in March 2022.1

A preliminary version published on July 2 from researchers at Yale University in the USA described a 60-year-old immunocompromised patient harboring a pre-existing variant, B.1.517, since November 2020.2 Researchers say it has evolved at twice the rate of infection with the wild-type SARS-CoV-2 virus, thanks to the patient’s lack of immunity. Lead author, Nathan Grupo, told the magazine Sciences Some of the viruses circulating in the patient today may qualify as new variants if they are found in the community.

Will all future variants come from Omicron?

At the time of writing, omicron is the only variant on the WHO’s list of ‘variables of concern’,3 Although it is divided into seven omicron ‘controlled sub-variables’: BA.4, BA.5, BA.2.12.1, BA.2.9.1, BA.2.11, BA.2.13, and BA.2.75.

“BA.5 is probably the worst version of the virus we’ve seen so far in terms of infection and its ability to escape immune,” Young says, although he thinks it will likely peak “very soon. , and then there will be another variable – omicron or not, we don’t know – appearing during the period from September to October.

“The biggest fear is that something will come from the left [as the existing variants and subvariants look to outcompete each other]A variant other than omicron is better adapted to infection and immune evasion.”

This will depend on where the new variant appears and the evolutionary advantages it has, in terms of transmission speed and immune evasion, as well as the immune status of the immediate population in which it finds itself.

To cite some previous examples, one study this year suggested that the gamma variant in New York City spread better in some areas — some of which were hit hardest in the first wave of the epidemic — with higher levels of pre-existing immunity.4 BA.5 led hospital admissions in Portugal (which has high levels of vaccination but also large numbers of elderly people) but not in South Africa. This may be due to a younger demographic but also to prior immunity from higher exposure to SARS-CoV-2 early in the epidemic.5

Do you have an “unanswered question due to Covid”? Email mlooi@bmj.com, we’ll try to cover it in a future installment of this series.

footnotes

  • Conflicts of interest: none.

  • Source and peer review: Commissioned, not external peer review.

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references

  1. Chagoza C, Han Am, Petroni Mi, et al. The accelerated development of SARS-CoV-2 within the host leads to distinct genotypes during chronic infection. medRxiv 2022 [preprint]. dui:10.1101 / 2022.06.29.22276868

  2. Vasylyeva TI, Fang CE, Su M, et al. Presentation and creation of the SARS-CoV-2 gamma variant in New York City in early 2021. medRxiv 2022 [preprint]. dui:10.1101 / 2022.04.15.22273909