As the Delta strain continues to spread so widely, experts are questioning whether the long-term goal of achieving herd immunity to the coronavirus through vaccination is still viable.
Herd immunity is achieved when a certain percentage of the world’s population is vaccinated against a pathogen or recovers from an infection. But questions arise about whether it can be achieved in the case of the Corona epidemic, with the emergence of new strains of the virus?
“If the question is, will vaccination alone allow us to control the epidemic?” The answer is “no,” epidemiologist Mircea Sofonia told AFP.
She added that herd immunity depends on two main factors: the infection of the virus and the effectiveness of vaccines.
Research has shown that the delta strain of the coronavirus is about 60 percent more transmissible than the alpha strain, and about twice the prevalence of the original strain of the virus, which emerged in late 2019.
The researchers emphasized that the more effective the virus became in infecting people, the higher the herd immunity threshold.
“In theory, it’s a very simple calculation,” said epidemiologist Antoine Flaholt. He added that for the original virus, which had a reproduction rate of between zero and three, which means that each infected person infects up to three others, it was possible to achieve herd immunity with about 66 percent of people immunized.
“But if the reproduction rate is eight, as is the case with Delta, that makes the herd immunity with 90% immunization.”
According to data published by US authorities this week, the effectiveness of the Pfizer and Moderna vaccines in preventing infection has decreased from 91 to 66 percent since the Delta strain became dominant.
Studies have shown that the effectiveness of the vaccine against Delta decreases over time, prompting many countries in the world to announce giving people a third booster dose of the vaccine.
Sofonia stated that in the absence of other health measures such as wearing masks or social distancing, it would need to immunize 100 percent of people in order to ensure the end of transmission, which is impossible.
“But even if the mythical dream of achieving herd immunity no longer exists, getting vaccinated remains very important,” said Andrew Pollard, director of the Oxford British Vaccine Group.
As with vaccines against other currently endemic diseases such as measles and influenza, corona vaccines provide excellent protection against severe symptoms of the virus.
“What scientists are recommending is to protect as many people as possible through vaccination,” Flaholt said. “In the end, of course, all epidemics end,” he continued.
Sofonia emphasized that it is still possible for Covid to turn into an endemic disease over time.
Scientists envision that until the near future people will continue to use masks and social distancing in certain areas in order to reduce transmission of the disease.
“During the AIDS pandemic, when scientists said we need to wear condoms, a lot of people said, ‘Okay, we’ll do that for a while. And eventually they keep using it. It’s possible that we can continue to use masks indoors and on transportation,” Flaholt said. For some time”.