Herd immunity not possible after all ?

Throughout the pandemic, I have supported the views of Professor Sunetra Gupta, who has consistently advocated a policy of focussed protection for the vulnerable whilst letting the younger fitter population to get infected with covid-19, thus acquiring herd immunity for the whole population. However, in recent days, other eminent scientists and epidemiologists are saying that herd immunity is not possible because of the delta variant. How can this be ?

A crowd of people eats at tables on a busy London street
Outdoor dining in London. 
Belinda Jiao/SOPA Images/LightRocket/Getty Images

“The Delta variant has changed the equation for achieving herd immunity, the developer of the Oxford/AstraZeneca vaccine has said. Speaking at a UK parliamentary meeting on Tuesday, Sir Andrew Pollard, a professor of pediatric infection and immunity at the University of Oxford, said that achieving herd immunity is “not a possibility” now that the Delta variant is circulating. “We know very clearly with coronavirus that this current variant, the Delta variant, will still infect people who have been vaccinated, and that does mean that anyone who’s still unvaccinated, at some point, will meet the virus,” Pollard said. He said it was unlikely that herd immunity will ever be reached, saying the next variant of the novel coronavirus will be “perhaps even better at transmitting in vaccinated populations.”

Fully vaccinated people can still get the delta variant, albeit as a milder case. I heard today that my brother and his wife recently tested positive to covid-19. Some experts had hoped that herd immunity could be reached with COVID-19, as was the case with measles, which is also highly infectious. Many countries have achieved herd immunity with measles by vaccinating 95% of the population against it, such as the US, where endemic transmission ended in 2000. That is because once a person is vaccinated against measles, they cannot transmit the virus. With COVID-19, vaccines still fulfil their primary role: protecting against severe disease. According to the US Centers for Disease Control and Prevention, vaccinated people who catch the Delta variant are 25 times less likely to have a severe case or die. The overwhelming majority who do catch it will have mild or no symptoms. But growing evidence suggests that, with the Delta variant, fully vaccinated people can still transmit the virus.

Israel is a good example of this: COVID-19 cases dropped in the country after it vaccinated about 80% of adults — prompting some to hope that it had reached herd immunity — but the Delta variant has since brought another surge of cases. click full source. So there we have it. The evidence sounds compelling but I will await the views of Professor Gupta. It is not clear to me how a level of herd immunity will not be achieved by most of the population contracting the delta variant whether they are vaccinated or not.

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