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9 marzo, 2022

How Will the Pandemic Evolve After the Omicron Variant?

France — During a round-table discussion at the French Senate, specialists in infectious disease and epidemiology presented their thoughts on what might happen after the Omicron wave passes. Will COVID become an endemic disease, or will new, worrisome variants emerge? Using various types of data, the experts shared their views which, while cautious, were reassuring all the same.

The “Russian Flu”

In his opening statement, Éric Caumes,MD, an infectious disease specialist at the Hôtel-Dieu Hospital in Paris, stressed that he wasn’t “looking into a crystal ball,” but rather that his focus, “ever since the epidemic started, has been on seeing what history can tell us.”

He brought up the fact that in the period of 1889-1890, there had been a coronavirus epidemic— which, unfortunately, was wrongly named “the Russian flu.”

The coronavirus at the origin of that epidemic was OC43. Back then, it caused over 500 deaths per day in Paris. Today, OC43 is one of four coronaviruses that no longer pose the threat they once did.

“What we learned about the OC43 epidemic is that there were several successive waves occurring in the winter as well as in the summer. The waves became increasingly spaced out, with fewer and fewer peaks, and herd immunity was achieved. These days, we’re able to live with OC43. That epidemic lasted 3 to 5 years, which is why I said that the current epidemic would last 3 to 5 years.”

Caumes’ “second focus” is based on the following guiding principle in the field of infectious diseases: when a virus mutates, when it becomes more transmissible, its pathogenicity decreases. This principle has been evident with Omicron.

“I think that it’s going to recede, with winter epidemics, but that it will eventually settle down like the other four coronaviruses before it. We can always come up with catastrophic scenarios later on, but I myself don’t lapse into that type of thinking. I must admit that the truth is that we just don’t know. However, based on the history of epidemics and infectious diseases, we do know that we can have an optimistic view of things for the medium term and the long term,” Caumes concluded.

What About Mutations?

Bruno Lina, MD, PhD, department head at the Institute of Infectious Agents at Lyon University Hospital and a member of France’s COVID-19 Scientific Advisory Board, presented his analysis and perspective on the evolution of viruses, with a particular focus on virological characteristics.

In his opinion, the two most likely hypotheses in the short term are the following:

  • Evolution by molecular and antigenic drift away from BA.1/Omicron (for example, BA.2)
  • Co-evolution: simultaneous molecular/antigenic drift away from Omicron and modifications in other genes that would confer a better ability to transmit and infect (that is,  fitness).

Less likely is the development of a new variant with a better ability to transmit and infect coming from the root (meaning the first viruses in China). “We can’t say that this risk doesn’t exist. It’s just that it’s not the most likely,” Lina pointed out.

However, he added, we should keep the following two problematic hypotheses in mind as possibilities:

  • A genetic recombination between SARS-CoV-2 and a human betacoronavirus (such as OC43). This could modify the pathogenesis; therefore, the virus’ evolution must be monitored by performing sequencing.
  • Reverse zoonosis starting in farm-raised animals (for example, cases of infected golden hamsters in Hong Kong, minks in Europe, deer in North America, pets, animals in zoos, etc.). “When the virus spills back from humans to animals, it recovers an evolutionary capacity that we must be extremely vigilant about. If this virus goes back to humans, that can end up creating a new root like the one that emerged in 2019,” the virologist noted.

Adapting Vaccines

Regarding the necessity of adapting vaccines to a virus that has become endemic or seasonal, Lina stressed that we didn’t know how frequently the vaccines would have to be modified, because “we don’t know the evolutionary dynamic of tomorrow’s virus.” Should it perhaps be on a seasonal basis, as in the case of the flu, or should we instead go by the evolution of the aforementioned OC43 virus, which had been mainly driven by immune escape and which took about 10 years? “For SARS-CoV-2, I don’t know which carries more weight: the evolutionary capacity in terms of fitness or the evolution induced by immune pressure.” In summary, it’s impossible to say for now whether vaccines will have to be adapted every year or adapted at some longer interval.

The Epidemiologist’s View

In her comments about short-term prospects, Vittoria Colizza, PhD, epidemiologist and research director at the Pierre Louis Institute of Epidemiology and Public Health (French National Institute of Health and Medical Research [INSERM]/Sorbonne University), noted Omicron’s rapid waning — a decrease that could speed up with the upcoming school breaks and the arrival of spring.

However, Colizza warned about the presence of the variant BA.2, which seems to spread more quickly. Still, whether it has an increased ability to transmit and/or a greater capacity to reinfect is unknown. Also, the first available data suggest that this variant is slightly better able to evade the immunity acquired against the previous variants, such as Delta and Alpha.

In Colizza’s opinion, two scenarios are more plausible for the longer term. The first is the emergence of new variants. “All the same, we have, in the rest of the world, an incidence that remains very high. Well, high incidence means that there’s a greater probability of having mutations that could become dominant.”

The second scenario is endemicity, like the kind one sees with the flu or other common illnesses. “One probable scenario is that once a certain number of layers of [natural or acquired] immunity have been built up, these layers will provide quite broad protection to the population.” But we don’t know how much time will be needed to get there. “We shouldn’t think that it’s going to be a 100-meter dash on a really well-lit track. Instead, it’s going to be more like a trail run with several obstacles along the path and a certain number of possible epidemic resurgences,” she explained.

She then moved on to the topic of anticipating waves of infection. “To date, vaccination campaigns have been running after the variants. Now, we’re expecting the viruses to be seasonal. This will allow vaccination campaigns to be scheduled. We must think ahead,” she concluded.

https://www.medscape.com/viewarticle/969757?src=soc_fb_220307_mscpedt_news_mdscp_omicron&faf=1#vp_1


Créditos: Comité científico Covid

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