Pollard said: "I think we are in a situation here with this current [delta] variant, where herd immunity is not a possibility because it still infects vaccinated individuals. [Anyone] who's still unvaccinated, at some point, will meet the virus … and we don't have anything that will stop that transmission."
The epidemiologist from the University of Oxford pointed out a stark difference between the B16172 delta variant and the measles virus. "If 95 percent of the people were vaccinated against measles, the virus cannot transmit in the population," Pollard told the All-Party Parliamentary Group on Aug. 10.
Pollard furthermore warned that new variants that can be more transmissible among the vaccinated may emerge. He said: "I suspect that what the virus will throw up next is a variant [that] is perhaps even better at transmitting among the vaccinated populations. [That's] even more of a reason not to be making a vaccine program around herd immunity."
Cardiff University School of Medicine's Dr. Andrew Freedman later expressed agreement with Pollard's remarks on herd immunity. He concurred with the Oxford epidemiologist's assessment that herd immunity was unlikely. He told CNBC on Aug. 12: "The delta variant is highly transmissible, meaning that the proportion of people needing to be fully vaccinated for herd immunity is probably not achievable."
Freedman acknowledged the effectiveness of the COVID-19 vaccines against severe disease, hospitalization and death. However, he noted that they are "less effective in preventing infection, mild disease and [viral] transmission" arising from the B16172 delta variant.
Herd immunity involves populations being protected from certain illnesses by means of antibodies produced by majority of people through inoculation and after a bout of disease. If enough people produce antibodies to fight the disease, only a few will fall sick. The pathogen responsible for the sickness will then have less opportunity to spread and infect other people.
Herd immunity also helps protect those who cannot be vaccinated through the population's overall immunity levels. Many countries rely on mass inoculation instead of natural means to achieve herd immunity. But clinical studies show that vaccine-induced immunity wanes over time. (Related: Policymakers ignoring natural immunity to covid in favor of "vaccine" immunity.)
A July 30 paper published in Scientific Reports claimed that people who receive the COVID-19 vaccine are responsible for the rise of vaccine-resistant SARS-CoV-2 variants. The researchers used statistical modeling to determine how Wuhan coronavirus strains mutate and bypass vaccine-induced immunity. They found that three primary risk factors – a high probability of the resistant strain's initial emergence, a high number of infected individuals and low vaccination rates – favored variants that resisted vaccines.
Study co-author Simon Rella of the Institute of Science and Technology Austria (ISTA) elaborated on his colleagues' findings. He told media outlets on Aug. 6: "When most people are vaccinated, the vaccine-resistant strain has an advantage over the original strain. This means the vaccine-resistant strain spreads through the population faster at a time when most people are vaccinated."
Fyodor Kondrashov, another study co-author, said their paper's finding followed the concept of selective pressure – the force that drives the evolution of organisms. The ISTA researcher explained: "Generally, the more people are infected, the [higher] the chances for vaccine resistance to emerge. By having a situation where you vaccinate everybody, a vaccine-resistance mutant [strain] actually gains a selective advantage."
"The highest risk of resistant strain establishment occurs when a large fraction of the population has already been vaccinated, but the transmission is not controlled," the study authors wrote. They also warned that once a large fraction of the population is inoculated, "policymakers and individuals will be driven to return to pre-pandemic guidelines and conducive to a high rate of virus transmission." (Related: Vaccinated people causing vaccine-resistant coronavirus strains to emerge: Study.)
Pandemic.news has more articles about herd immunity against COVID-19.