Israel Reports Lower Vaccine Efficacy Against Delta Variant

Photo: Reuters

New data from Israel suggests a lower efficacy for the Pfizer vaccine against infections caused by the delta variant.

Earlier this week, Israel’s health ministry reported a significant drop in the efficacy of the Pfizer vaccine. They reported a decline in vaccine efficacy against mild COVID-19 caused by the delta variant. However, as per the results, the vaccine continues to protect against severe disease.

Israel began its vaccine rollout in December of last year. 57% of the country’s population is now fully vaccinated thanks to the effective vaccine drive. Therefore, making the population a target for case studies assessing vaccine effectiveness in controlling cases and deaths. However, over the past few weeks, the number of cases has significantly increased.

According to Ran Balicer, chairman of Israel’s national expert panel on COVID-19, the number of severe COVID-19 cases have risen from one every 2 days to 5 cases per day. Moreover, the advancing delta variant has resulted in 300 new coronavirus cases per day. Half of these cases occurred among vaccinated adults.

The Israeli news site Ynet reported that prior to June 6, efficacy of the Pfizer vaccine against COVID-19 was an average of 94.3%. After June 6, as the country lifted its COVID-19 restrictions and the delta variant began to spread, the efficacy dropped to 64%. However, the effectiveness of preventing hospitalizations only saw a slight shift from 98.2 to 93%. They reported a similar decrease against severe COVID-19. Thus, providing evidence of the vaccine’s continuing benefit.

‘Too Early to Assess Effectiveness’

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

Ran Balicer, chairman of Israel’s national expert panel on COVID-19

Although the rising numbers are concerning, Israel’s health experts believe it is too early to assess the extent of the Delta variant’s effect on vaccine efficacy. Citing Israel’s small number of cases among vaccinated individuals is a huge limiting factor. Moreover, researchers suggest that the rise in cases could have happened before the vaccinated individual developed an immune response. A person is fully vaccinated around 2 weeks after their second dose. Because that’s how long it takes for the development of antibodies.

Pfizer is yet to comment on the data coming in from Israel. However, the company did cite a study that had demonstrated its vaccine’s efficacy against lab-made versions of the Delta variant.  

The Israeli government has now reintroduced its coronavirus restrictions such as wearing masks indoors in public spaces. They are also looking into a booster dose for the vaccinated adult population. Previously, Pfizer CEO Albert Bourla had predicted the need of a booster dose within 12 months of the initial doses.


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