Israeli news site Ynet has reported that based on the number of cases of COVID-19 breakthrough infection reported by the Israeli Health Ministry, the efficacy of the Pfizer/BioNTech vaccine against mild cases caused by the Delta variant appears to have decreased. Fortunately, the vaccine appears to still be highly effective against the most serious cases.
The reported numbers suggested that between May 2 and June 5, the efficacy against the disease was around 94 percent. Since June 6, the efficacy appears to have decreased to 64 percent. When it comes to hospitalizations, the efficacy seems to drop only marginally from 98.2 percent to 93 percent.
While the drop in efficacy is concerning, it is important to state that there could be several factors at play here, and we should wait for more data to begin to build a complete picture. One possibility, also seen in other countries, it’s that the infections happened before a strong immune response might have developed. Fully vaccinated people are counted from the moment they get the second jab of the two-dose vaccines, but strong immunity doesn’t really kick in until at least two weeks later.
The Israeli government is considering reintroducing social distancing measures. These were lifted mid-June, but things like masks in closed spaces came back on June 25. They are also considering a booster vaccination campaign, although the percentage of vaccinated people, while high, remains below the threshold for herd immunity.
Breakthrough infections are to be expected simply because vaccines are not 100 percent effective. The danger lies in infections being allowed to propagate through a population uncurbed. A new variant of the disease could emerge, against which the vaccines are ineffective. Fortunately, this has not happened yet.