Reaching herd immunity is "not a possibility" with the current Delta variant, the head of the Oxford Vaccine Group has said. Giving evidence to MPs on Tuesday, Prof Sir Andrew Pollard said the fact that vaccines did not stop the spread of Covid meant reaching the threshold for overall immunity in the population was "mythical." "The problem with this virus is [it is] not measles. If 95% of people were vaccinated against measles, the virus cannot transmit in the population," he told the all-party parliamentary group (APPG) on coronavirus. "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 ... and we don't have anything that will [completely] stop that transmission."
Although the existing vaccines are very effective at preventing serious Covid illness and death, they do not stop a fully vaccinated person from being infected by the virus that causes Covid-19. The concept of herd or population immunity relies on a large majority of a population gaining immunity -- either through vaccination or previous infection -- which, in turn, provides indirect protection from an infectious disease for the unvaccinated and those who have never been previously infected. Data from a recent React study conducted by Imperial College London suggests that fully vaccinated people aged 18 to 64 have about a 49% lower risk of being infected compared with unvaccinated people. The findings also indicated that fully vaccinated people were about half as likely to test positive after coming into contact with someone who had Covid (3.84%, down from 7.23%).
