Ómicron reveals how the hope of group immunity is extinguished

It is unlikely that the variant omicron, which spreads much faster than previous mutations of the coronavirus, help countries achieve so-called herd immunity against the virus. COVID-19, in which enough people become immune to the virus to curb the spread, disease experts said.

From the earliest days of the pandemic, some public health officials expressed hope that herd immunity against COVID-19 could be achieved, provided a sufficient percentage of the population was vaccinated or infected with the virus.

Hopes were dashed when the coronavirus mutated into new variants in rapid succession over the past year, allowing it to reinfect people who were vaccinated or had previously contracted COVID-19.

Some health authorities have revived the possibility of herd immunity since omicron appeared late last year.

They argue that the fact that the variant spreads so quickly and causes milder illness could soon expose enough people, in a less harmful way, to the SARS-COV-2 virus and provide herd protection.

Disease experts point out, however, that omicron’s transmissibility is aided by the fact that this variant is even better than its predecessors at infecting vaccinated or previously infected people. This adds to evidence that the coronavirus will continue to find ways to get past our immune defenses, they said.

“Reaching a theoretical threshold beyond which transmission will cease is probably unrealistic given the experience we have had in the pandemic,” Dr Olivier le Polain, an epidemiologist at the World Health Organization (WHO), told Reuters.

This is not to say that prior immunity offers no benefit. Rather than herd, many experts interviewed by Reuters said there is growing evidence that vaccinations and prior infection would help bolster the population’s protection against COVID-19, making the disease less severe. for those who become infected or reinfected.

“As long as population immunity holds up with this variant and future ones, we’ll 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.

It’s not like measles

Current COVID-19 vaccines are primarily designed to prevent severe illness and death, rather than infection. But the results of clinical trials in late 2020, in which two of the vaccines were shown to be more than 90% effective against the disease, initially raised hopes that the virus could be contained through widespread vaccination, similar to how measles has been stopped.

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

“The first is that immunity, especially to infection, which is the important type of immunity, declines fairly rapidly, at least with the vaccines that we have now.”

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 diminished.

Dr. David Wohl, an infectious disease specialist at the University of North Carolina School of Medicine at Chapel Hill, said “the rules change when vaccinated people can continue to harbor the virus and infect others.”

Wohl cautioned against assuming that infection with omicron would increase protection, especially against the next variant that might emerge. “Just because you had omicron, maybe that protects you from getting omicron again, maybe,” he added.

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

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

“These things appeared in the media: ‘We will reach herd immunity when 60% of the population is vaccinated’ and it has not happened. Then for 80%, and again it didn’t happen,” said Francois Balloux, a professor of computational biological systems at University College London.

“As horrible as it sounds, I think we have to prepare for the fact that the vast majority, essentially the entire world, will be exposed to SARS-CoV-2,” he said.

World health experts predict that the coronavirus will end up becoming endemic, circulating persistently among the population and causing sporadic spikes. However, the appearance of omicron has raised questions about when exactly it might occur.

“We will get there,” said the WHO’s le Polain, “but we are not there at the moment.”