Herd immunity is “legendary” with the Covid Delta variant, consultants say

In this photo illustration, a woman has a syringe in her arm

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Achieving herd immunity with Covid-19 vaccines if the highly infectious Delta variant spreads is “not an option,” a leading epidemiologist said the virus will be stopped – is unlikely for several reasons.

Professor Andrew Pollard, the head of the Oxford Vaccine Group, told UK lawmakers on Tuesday that the idea of ​​achieving herd immunity as Covid vaccines did not completely stop the spread of the virus – as vaccinated people are still getting infected and transmitting the virus can -, “mythical.”

“I think we are here with this current variant (the Delta variant) in a situation in which herd immunity is not possible because it is still infecting people who have been vaccinated,” said Pollard, one of the leading researchers when the AstraZeneca was founded. Oxford University vaccine said.

“And that means that anyone who is still unvaccinated will encounter the virus at some point. It might not be this month or next month, it could be next year, but at some point they will encounter the virus and we don’t have something to stop that transmission. “

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

What is Herd Immunity?

Put simply, herd immunity refers to the idea that both natural infection (through the formation of antibodies when fighting a virus) and vaccination can achieve high immunity to a virus in a population.

The latter method is preferred because, unlike the natural route of infection, vaccines produce predominantly immunity without causing disease or adverse health complications.

The antibodies obtained from both natural infection and vaccination usually protect against future infection, and when enough people in a population are immune, it results in a lower prevalence of disease or virus in a community. When a virus has fewer opportunities to spread and infect it can be tightly controlled or even eradicated.

In herd immunity, those who are not vaccinated (be it voluntarily or because they cannot be vaccinated at some point – for example, newborns) are protected by the overall level of immunity in a population.

Successful mass vaccination programs have resulted in deadly, contagious viruses and diseases such as polio, tuberculosis and measles being largely eradicated in parts of the world or being severely suppressed by vaccination programs and the herd immunity they promote.

Pollard stated on Tuesday that Covid and the current virulent Delta variant are different. “The problem with this virus is this [it is] no measles. If 95% of people were vaccinated against measles, the virus cannot be spread in the population, ”he told the UK all-party parliamentary group on the coronavirus.

Pollard said that while Covid vaccines could slow the spread of the virus – because in studies fully vaccinated but infected people shed fewer viruses, giving the virus less opportunity to spread – new variants would likely emerge that would spread as well.

“I suspect that the virus will next produce a variant that may be even better transmitted among vaccinated populations.

People fully vaccinated against Covid-19 are highly protected from serious infections, hospitalizations, and deaths from the virus. New research from the UK published last Friday also showed that people who were double-vaccinated were three times less likely to test positive for the coronavirus than those who were not vaccinated. The study, led by Imperial College London, also found that fully vaccinated people may be less likely to pass the virus on to others than those who are not.

Experts urge all unvaccinated people to come forward, but problems are emerging in some countries in Europe and the US as younger adults fail to take the vaccine.

Andrew Freedman, an infectious disease reader 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, which means that the proportion of people who need to be fully vaccinated for herd immunity is unlikely to be achievable,” he noted. “The vaccines offer very effective protection against serious illness / hospitalization / death, but are less effective in preventing infections, mild illnesses and transmission, especially with the Delta variant.”

In countries like the UK, herd immunity is also unlikely due to the large pool of unvaccinated adolescents and children – some of whom have immunity after natural infection, but most of whom do not, Freedman noted.

“But even without complete ‘herd immunity’, the higher the percentage of the fully vaccinated population, the lower the infection rate in the community,” he said.

Herd immunity problems

As the coronavirus pandemic spread around the world in 2020, a number of governments, such as those in Sweden and the UK, seemed ready to put their hopes on the concept of “herd immunity” and willing to allow the virus to spread among populations so that a natural immunity can build up.

The approach was quickly abandoned by the UK, however, as it quickly became apparent how deadly and destructive Covid could be, with thousands of infections resulting in hospitalizations and deaths threatening to overwhelm the healthcare system.

Achieving herd immunity to Covid is viewed as much more difficult for a number of other reasons, including uneven vaccine introductions, vaccination hesitation, and mutation of the virus, with new variants threatening (but not yet undermining) the effectiveness of the Covid vaccine.

Read more: Will herd immunity ever be possible with the spread of Covid mutations?

In addition, experts do not yet know how long immunity to Covid lasts, although there is clinical evidence that immunity to the virus (whether that immunity is acquired naturally through infection or vaccination) wears off over time.

Studies show that the Covid vaccines used in Europe and the US are still highly effective in preventing serious infections, hospitalizations and deaths. Although there are indications of so-called “breakthrough” covid cases in people who have been completely vaccinated, these cases are very rare and tend to be milder.

Danny Altman, a professor of immunology at Imperial College London, told CNBC that he also agrees with Pollard and that the mathematical model of herd immunity cannot simply be applied to an “unprecedented” virus like Covid that is created with divergent, globally circulating variants.

“The whole herd immunity thing was one of those pieces of medical textbook language that was adopted early by policy advisers, then by the press, then by the public, and consistently skewed and oversimplified,” he said Thursday.

According to Altmann, it is important that “the more people in the world are effectively vaccinated, the fewer virus copies we will have on the planet, i.e. the less spread and fewer lungs in which the virus will mutate and the next wave of variants.”

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