Analysis: How Omicron highlights the fading hope of herd immunity against COVID-19


ANALYSIS-How Omicron highlights the fading hope of herd immunity against COVID

Chicago: The Omicron variant, which spreads much faster than previous versions of the coronavirus, is unlikely to help countries achieve so-called herd immunity against COVID-19, in which enough people become immune against the virus that it can no longer spread, say leading disease experts.

From the earliest days of the pandemic, public health officials expressed hope that it was possible to achieve herd immunity against COVID-19, as long as a sufficiently high percentage of the population was vaccinated or infected. by the virus.

Those hopes have faded as the coronavirus has mutated into new variants in rapid succession over the past year, allowing it to re-infect people who have been vaccinated or have already contracted COVID-19.

Some health officials have raised the possibility of herd immunity since Omicron emerged late last year.

The fact that the variant spreads so quickly and causes milder disease could soon expose enough people, in less harmful ways, to the SARS-COV-2 virus and provide that protection, they say.

Disease experts note, however, that the transmissibility of Omicrons is aided by the fact that this variant is even better than its predecessors at infecting people who have been vaccinated or have had a previous infection. This adds to the evidence that the coronavirus will continue to find ways to break through our immune defences, they said.

Reaching a theoretical threshold beyond which transmission will cease is likely unrealistic given our experience with the pandemic, World Health Organization (WHO) epidemiologist Dr Olivier le Polain told Reuters. .

This is not to say that prior immunity offers no benefit.

Instead of herd immunity, many experts interviewed by Reuters said there was growing evidence that vaccines and previous infection would help build population immunity to COVID-19, which which makes the disease less severe for those who are infected or re-infected.

As long as population immunity holds up with this variant and future variants, we will be lucky and the disease will be manageable, said Dr David Heymann, professor of infectious disease epidemiology at the London School of Hygiene and Tropical Medicine.

Not like measles

Current COVID-19 vaccines were primarily designed to prevent serious illness and death rather than infection. But clinical trial results in late 2020 showing two of the vaccines were more than 90% effective against the disease initially raised hopes that the virus could be largely contained by widespread vaccination, in the same way that measles has was inhibited by the inoculation.

With SARS-CoV-2, two factors have since undermined that picture, said Marc Lipsitch, epidemiologist at Harvard TH Chan School of Public Health.

“The first is that immunity, especially against infection, which is the important type of immunity, wanes quite rapidly, at least with the vaccines we have now,” he said.

The second is that the virus can rapidly mutate in a way that allows it to evade protection from vaccination or previous infection – even when immunity has not waned.

“It’s a game-changer when vaccinated people can still spread the virus and infect other people,” said Dr. David Wohl, an infectious disease specialist at the University of North Carolina at Chapel Hill School of Medicine.

He cautioned against assuming that infection with Omicron would increase protection, especially against the next variant that might arise. “Just because you had Omicron might not stop you from having Omicron again,” Wohl said.

Vaccines in development that provide immunity against future variants or even multiple types of coronavirus could change that, said Pasi Penttinen, the top flu expert at the European Center for Disease Prevention and Control, but it will take time.

Still, the hope of herd immunity as a ticket back to normal life is hard to shake.

“These things were in the media: ‘Well, achieve herd immunity when 60% of the population is vaccinated. This does not happen.

Then for 80%. Again, that didn’t happen, Francois Balloux, professor of computational systems biology at University College London, told Reuters.

Horrible as it sounds, I think we have to be prepared for the fact that the vast majority, basically everyone, will be exposed to SARS-CoV-2,” he said.

Global health experts expect the coronavirus to eventually become endemic, persistently circulating in the population and causing sporadic outbreaks. Omicron’s emergence, however, raised questions about exactly when this might happen.

We’ll get there,” said WHO’s Polain, “but we’re not there yet.


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