Home Business Herd immunity is ‘mythical’ with the Covid delta variant, experts say

Herd immunity is ‘mythical’ with the Covid delta variant, experts say

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In this photo illustration a woman has an injection in her arm

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LONDON — Achieving herd immunity with Covid-19 vaccines when the highly-infectious delta variant is spreading is “not a possibility,” a leading epidemiologist has said, with experts agreeing that such a goal — where overall immunity in a population is reached and the spread of the virus is stopped — is not likely for several reasons.

Professor Andrew Pollard, the head of the Oxford Vaccine Group, told British lawmakers Tuesday that as Covid vaccines did not stop the spread of the virus entirely — with vaccinated people still able to be infected and transmit the virus — the idea of achieving herd immunity was “mythical.”

“I think we are in a situation here with this current variant (the delta variant) where herd immunity is not a possibility because it still infects vaccinated individuals,” Pollard, one of the lead researchers in the creation of the AstraZeneca-University of Oxford vaccine, said.

“And that does mean that anyone who’s still unvaccinated, at some point, will meet the virus. That might not be this month or next month, it might be next year, but at some point they will meet the virus and we don’t have anything that will stop that transmission.”

Read more: Fully vaccinated people are still getting infected with Covid. Experts explain why

What is herd immunity?

Put simply, herd immunity relates to the idea that a high level of immunity to a virus in a population can be achieved by both natural infection (through the forming of antibodies when the body fights a virus) and by vaccination.

The latter method is preferred as vaccines overwhelmingly create immunity without causing illness or adverse health complications, unlike the natural infection route.

The antibodies procured by both natural infection and vaccination usually protect against future infection and if enough people in a population are immune this leads to lower rates of prevalence of disease or viruses in a community. If a virus has less opportunity to spread and infect, it can be greatly controlled or even eradicated.

With herd immunity, those who are not vaccinated (whether through choice or because they cannot be immunized at a given point — newborn babies, for example) are protected by the overall level of immunity present in a population.

Mass, successful vaccination programs have meant deadly, contagious viruses and diseases such as polio, tuberculosis and measles have been largely eradicated in parts of the world or greatly suppressed by vaccination programs and the herd immunity they foster.

Experts are calling on all unvaccinated individuals to come forward, but there are issues emerging in some countries in Europe and the U.S. with younger adults not taking up the vaccine.

Andrew Freedman, reader in infectious disease at Cardiff Medical School, told CNBC Thursday that he agreed with Pollard’s diagnosis that herd immunity was an unlikely prospect.

“The delta variant is highly transmissible meaning that the proportion of people needing to be fully vaccinated for herd immunity is probably not achievable,” he noted. “The vaccines provide very effective protection against severe disease/hospitalisation/death but are less effective in preventing infection, mild disease and transmission, especially for the delta variant.”

In countries like the U.K., herd immunity was also unlikely due to the large pool of unvaccinated adolescents and children — some of whom would have immunity following natural infection but most would not, Freedman noted.

“However, even without complete ‘herd immunity,’ the higher the proportion of the population fully immunised, the lower the incidence of infection in the community,” he said.

Problems with herd immunity

Medical workers with Delta Health Center wait to vaccinate people at a pop-up Covid-19 vaccination clinic in this rural Delta community on April 27, 2021 in Hollandale, Mississippi.

Spencer Platt | Getty Images

Studies show that the Covid vaccines in use in Europe and the U.S. are still highly effective at preventing severe infections, hospitalizations and deaths. While there is evidence of so-called “breakthrough” Covid cases among fully vaccinated people, these cases are very rare and tend to be milder.

Danny Altman, professor of immunology at Imperial College London, told CNBC that he also agreed with Pollard and that the herd immunity mathematical model could not easily be applied to an “unprecedented” virus like Covid that was still little-understood with diverging, globally circulating variants emerging.

“The whole herd immunity thing was one of those bits of medical textbook-speak that was adopted early on by policy advisors, then the press, then the public and has throughout been contorted and over-simplified,” he said Thursday.

What was important, Altmann said, was that “the more people on the globe effectively vaccinated, the fewer viral copies we’ll have on the planet, thus the less spread and fewer lungs in which for virus to mutate and spread the next wave of variants.”

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