Cracks in vaccines means prospect of herd immunity is a pipe dream
It was not long ago that we dared hope vaccines would prevent not just serious illness from Covid-19 but the bulk of onward transmission. No more, alas.
All over the world people who have received two jabs of the vaccine are being infected with the virus, albeit mildly for the most part.
The first hint of an issue came from Israel in July, when its health ministry released data suggesting the Pfizer jab’s effectiveness at preventing symptomatic infection had slipped from 94 to 64 per cent with the arrival of the delta variant.
In the UK, the latest findings from a survey led by Imperial College London found fully vaccinated individuals had only a 50 to 60 per cent reduced risk of infection once asymptomatic carriers were taken into account. “The delta variant is known to be highly infectious and, as a result, we can see from data that breakthrough infections are happening in fully vaccinated people,” said Prof Steven Riley of Imperial.
A US study, published on Tuesday, suggests that, of the two vaccines using M-RNA technology, the Moderna may outperform Pfizer-biontech by quite a margin as far as breakthrough infections are concerned.
In a study of more than 50,000 patients in the Mayo Clinic Health System, it was found the effectiveness of Moderna’s vaccine against infection had dropped to 76 per cent in July – when the delta variant was predominant. Over the same period, the effectiveness of the Pfizer shot had fallen to just 42 per cent.
Typically, the UK’S dominant Astrazeneca jab comes in third place in comparisons of effectiveness.
On the positive side, all UK authorised vaccines still provide excellent protection against severe disease and death.
However, without a vaccine that completely blocks infection things change. First, the prospect of herd immunity goes out the window. “This virus is not measles,” Prof Sir Andrew Pollard, director of the Oxford Vaccine Group, warned.
“We know very clearly with the coronavirus that 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.”
Prof Francois Balloux, director of the UCL Genetics Institute said: “It is not so much, anymore, a duty to others to get vaccinated but a protection for oneself.
“There won’t be any herd immunity wall to hide behind.”
Festivals and other mass events are already switching their entry requirements to require a negative test – even where visitors have been double vaccinated.
International travel schemes such as the EU Covid certificate could also be tightened, with testing once again becoming a requirement.
But we should never say never when it comes to Covid. Scientists are already testing vaccines delivered directly into the sinuses to give better protection against breakthrough infections.