Rising coronavirus cases in Israel, where most residents are inoculated with the Pfizer/BioNTech vaccine, offer “a preliminary signal” the vaccine may be less effective in preventing mild illness from the Delta variant, a top expert said Monday.
But Ran Balicer, chairman of Israel’s national expert panel on COVID-19, stressed it was “too early to precisely assess vaccine effectiveness against the variant” first identified in India in April that is surging across the globe.
That is partly due to the overall low number of cases among fully vaccinated Israelis, and because exposure to the virus and the likelihood of being tested are not evenly distributed across the population, further complicating efforts to reach conclusions about the data.
Balicer, also the chief innovation officer at Clalit, Israel’s largest health maintenance organisation (HMO), told AFP that the Delta variant’s emergence as the “dominant strain” in the country has led to a “massive shift in the transmission dynamic”.
Israel’s vaccine rollout that began in December was one of the world’s fastest, making the Jewish state a closely-watched case study on whether mass inoculation offers a path out of the pandemic.
Vaccinations had brought transmission down to about five local new cases per day, but that figure has risen to around 300 in recent days, with the Delta variant raging.
About half of the daily cases are among children, and half are among mostly vaccinated adults.
“To some extent that could be expected since 85 percent of Israeli adults are vaccinated,” Balicer said.
“But the rates in which we see these breakthrough cases make some believe they extend beyond that expected point and suggest some decrease in vaccine effectiveness against mild illness—but not severe illness—is likely.”
The number of severe cases among vaccinated Israelis has risen in recent days from roughly one every two days up to five cases per day, Balicer said.
He said it was also too early to draw conclusions about the vaccine’s effectiveness against serious illness caused by the Delta variant.
Israeli Prime Minister Naftali Bennett warned Sunday, ahead of a weekly cabinet meeting, that “with the Delta variant running amok,” Israel may have to reintroduce certain restrictions that were lifted last month to curb transmission.
Balicer said it was unlikely Israel could contain rising cases without further restrictions being reimposed, but voiced hope they would be mild and that Israel’s “vaccine wall” of inoculated citizens will help reduce further spread.
“It is encouraging that we still maintain zero deaths for the last twelve days,” he further said.
Vaccines are proving to be highly effective in controlling hospitalisation and deaths associated with SARS-CoV-2 infection but the emergence of viral variants with novel antigenic profiles threatens to diminish their efficacy. Assessment of the ability of sera from vaccine recipients to neutralise SARS-CoV-2 variants will inform the success of strategies for minimising COVID19 cases and the design of effective antigenic formulations.
Here, we examine the sensitivity of variants of concern (VOCs) representative of the B.1.617.1 and B.1.617.2 (first associated with infections in India) and B.1.351 (first associated with infection in South Africa) lineages of SARS-CoV-2 to neutralisation by sera from individuals vaccinated with the BNT162b2 (Pfizer/BioNTech) and ChAdOx1 (Oxford/AstraZeneca) vaccines.
Across all vaccinated individuals, the spike glycoproteins from B.1.617.1 and B.1.617.2 conferred reductions in neutralisation of 4.31 and 5.11-fold respectively. The reduction seen with the B.1.617.2 lineage approached that conferred by the glycoprotein from B.1.351 (South African) variant (6.29-fold reduction) that is known to be associated with reduced vaccine efficacy.
Neutralising antibody titres elicited by vaccination with two doses of BNT162b2 were significantly higher than those elicited by vaccination with two doses of ChAdOx1.
Fold decreases in the magnitude of neutralisation titre following two doses of BNT162b2, conferred reductions in titre of 7.77, 11.30 and 9.56-fold respectively to B.1.617.1, B.1.617.2 and B.1.351 pseudoviruses, the reduction in neutralisation of the delta variant B.1.617.2 surpassing that of B.1.351.
Fold changes in those vaccinated with two doses of ChAdOx1 were 0.69, 4.01 and 1.48 respectively. The accumulation of mutations in these VOCs, and others, demonstrate the quantifiable risk of antigenic drift and subsequent reduction in vaccine efficacy.
Accordingly, booster vaccines based on updated variants are likely to be required over time to prevent productive infection. This study also suggests that two dose regimes of vaccine are required for maximal BNT162b2 and ChAdOx1-induced immunity.
reference link : https://www.medrxiv.org/content/10.1101/2021.06.23.21259327v1