The Israeli data stands in contrast to a study in England carried out from April to May that found that, after two doses, the Pfizer-BioNTech vaccine was 88% effective against symptomatic disease caused by the delta variant.
Comparing the results is tricky, however, given variances in the nature of the vaccination programs in both countries (Israel gave all its adult population the Pfizer vaccine, for example, while in the U.K. there are several vaccines in use, with the Pfizer-BioNTech shot predominantly given to younger people) as well as differences in the study dates, age groups and Covid testing regimes involved.
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Similarly to the Israeli data, the English data also concluded that after two doses the Pfizer-BioNTech Covid vaccine is highly effective against hospitalization from the delta variant (the English data found the vaccine to be 96% effective, the Israeli data found it to be 88% effective against hospitalization, on average). In addition, English data found that the Oxford-AstraZeneca vaccine was 92% effective in preventing hospitalization after two doses.
Professor Lawrence Young, a virologist at the University of Warwick’s Medical School in the U.K., told CNBC that cases of Covid in fully vaccinated people are a reminder that “no vaccine is 100% effective.” “There will always be a proportion of individuals who will still remain susceptible to infection and illness,” he said Monday.
“There are also two other factors that impact vaccine effectiveness: (1) waning immunity — we still don’t know how long vaccine-induced protective immunity lasts. This is very likely to be a factor in those elderly and more vulnerable individuals who were vaccinated early in the vaccine rollout program,” he noted.
The second factor, he added, related to “breakthrough infections in vaccinated individuals due to the more infectious delta variant” which added weight to the case for booster vaccination programs, he said. As yet, the jury is still out on booster programs with a decision yet to be made in the U.S. and U.K.
It’s difficult to know the full extent of “breakthrough” Covid cases because cases in vaccinated people tend to be mild or asymptomatic and could go easily go unnoticed, but figures collected by NBC News has found that at least 125,000 fully vaccinated Americans have tested positive for Covid and 1,400 of those have died. Still, the 125,682 “breakthrough” cases in 38 states found by NBC News represented less than 0.08% of the 164.2 million-plus people (and counting) who have been fully vaccinated since the start of the year, or about one in every 1,300.
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That is, the number of cases and deaths among the vaccinated is very small compared to the number among the unvaccinated. Health officials, particularly in the States, are urging unvaccinated people to come forward for Covid immunization.
Steven Riley, a professor of infectious disease dynamics at Imperial, said that so-called “breakthrough infections” in fully vaccinated people needed to be studied further, particularly as parts of the world contend with the spread of the delta variant. “The delta variant is known to be highly infectious, and as a result we can see from our data and others’ that breakthrough infections are happening in fully vaccinated people. We need to better understand how infectious fully vaccinated people who become infected are, as this will help to better predict the situation in the coming months, and our findings are contributing to a more comprehensive picture of this.”