The spread of the delta variant has caused the number of people infected with COVID-19 in Britain to jump to almost six times as many within a month, but there has not been a reported increase in the number of serious cases or deaths from the new strain, compared to previous strains, due, it is believed, to the efficacy of the vaccine.
The delta strain of the coronavirus, first reported in October in India, has now become the dominant strain worldwide, and has spread to more than 80 countries. Although the virus is much more contagious than previous strains, it has not resulted in higher morbidity in Britain.
The term “vaccine efficacy” includes a number of important parameters, each of which is critical, both in terms of the individual as the broader epidemiological picture of management of the virus.
The spread of the virus includes two basic steps. The first is contraction of the virus following exposure. The second is the disease caused by the virus and its multiplication in the body, in this case, COVID-19.
The data on the spread of the virus in Britain recently illustrate the difference between these two steps with regard to the efficacy of the vaccine. In recent weeks, the delta variant has become particularly dominant in Britain. On May 22, the daily number of newly infected people was 1,739. A month later, on June 22, in the midst of Britain’s vaccination campaign, that number spiked to 10,149. However, the number of people hospitalized with COVID-19 rose by much less.
It takes about a month to reflect the period of time between exposure to the virus and developing the disease to an extent requiring hospitalization.
The possible explanation for the difference between these two figures could be the gap between the ability of the vaccine to prevent and pass on the infection, and its efficacy in stopping the multiplication of the virus, causing a more severe effect on the body, especially the cells in the respiratory and immune systems.
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According to Prof. Ran Balicer, chief innovation officer at Clalit Health Services and head of the committee of experts advising the Health Ministry on COVID-19, Britain, which has one of the highest vaccination rates in the world, has been unable to stop the spread of the delta variant “both because it is more infectious, and because the vaccine is less effective than it was first thought it would be in stopping light cases of the virus, and stands at 88 percent."
"There is a rise in hospitalizations with this variant, but it is more moderate because it infects more young people than older adults, and because many of the adults that become infected are vaccinated and protected from serious illness,” Balicer explained.
The protection the vaccination affords from the delta variant of COVID-19 is no less than against the original strain, and at this point there is no quality data attesting that the delta variant is more violent than previous strains, Balicer said. Based on the data from Britain, it is believed that vaccination with the Pfizer vaccine reduces the risk of hospitalization by 25 percent, Balicer said.
While not enough time has passed to determine the impact of the disease caused by the delta variant, so far Britain has not seen increased morbidity as a result of it. This, Balicer said, raises hope that vaccination prevents older adults from contracting many of the fatal complications from the coronavirus that are typical of their age group.
“In Israel we are in a better position to stop the spread [of the virus] than in Britain because the percentage of vaccinated older adults is much higher in Israel – more than 85 percent, compared to 60 percent, and the Pfizer vaccine is more effective than other vaccines given there.”