Delta variant key to breakthrough infections in vaccinated Israelis


Israeli officials are reporting a 30% decrease in the effectiveness of the Pfizer/BioNTech vaccine to prevent SARS-CoV-2 infection and mild to moderate cases of COVID-19. At the same time, protection against hospitalization and severe illness remains robust.

The country’s Ministry of Health data cited high levels of circulating Delta variant and a relaxation of public health measures in early June for the drop in the vaccine’s prevention of “breakthrough” cases from 94% to 64% in recent weeks.

However, it is important to consider the findings in context, experts cautioned.

“My overall take on this that the vaccine is highly protective against the endpoints that matter – hospitalization and severe disease,” Anna Durbin, MD, told this news organization.

“I was very pleasantly surprised with the very high efficacy against hospitalization and severe disease – even against the Delta variant,” added Dr. Durbin, professor of medicine at Johns Hopkins University, Baltimore.

Ali Mokdad, PhD, of the Institute for Health Metrics at the University of Washington, Seattle, agreed that the high degree of protection against severe outcomes should be the focus.

“That’s the whole idea. You want to defend against COVID-19. So even if someone is infected, they don’t end up in the hospital or in the morgue,” he said in an interview.

Compared with an earlier report, the efficacy of the Pfizer vaccine against hospitalization fell slightly from 98% to 93%.

“For me, the fact that there is increased infection from the Delta variant after the vaccines such as Pfizer is of course a concern. But the positive news is that there is 93% prevention against severe disease or mortality,” added Dr. Mokdad, who is also professor of global health at University of Washington.

In addition, the absolute numbers remain relatively small. The Ministry of Health data show that, of the 63 Israelis hospitalized with COVID-19 nationwide on July 3, 34 were in critical condition.

Unrealistic expectations?

People may have unrealistic expectations regarding breakthrough infections, Dr. Durbin said. “It seems that people are almost expecting ‘sterilizing immunity’ from these vaccines,” she said, explaining that would mean complete protection from infection.

Expectations may be high “because these vaccines have been so effective,” added Dr. Durbin, who is also affiliated with the Johns Hopkins Center for Global Health.

The higher the number of vaccinated residents, the more breakthrough cases will be reported, epidemiologist Katelyn Jetelina, PhD, MPH, assistant professor of epidemiology, human genetics, and environmental sciences at the University of Texas Science Center at Houston, wrote in her “Your Local Epidemiologist” blog.

This could apply to Israel, with an estimated 60% of adults in Israel fully vaccinated and 65% receiving at least one dose as of July 5, Our World in Data figures show.

How the updated figures were reported could be confusing, Dr. Jetelina said. Israel’s Health Minister Chezy Levy noted that “55% of the newly infected had been vaccinated” in a radio interview announcing the results.

“This language is important because it’s very different than ‘half of vaccinated people were infected,’ ” Dr. Jetelina noted.

Israel had a 7-day rolling average of 324 new confirmed COVID-19 cases as of July 5. Assuming 55% of these cases were among vaccinated people, that would mean 178 people experienced breakthrough infections.

In contrast, almost 6 million people in Israel are fully vaccinated. If 55% of them experienced breakthrough infections, the number would be much higher – more than 3 million.

Dr. Jetelina added that more details about the new Israel figures would be helpful, including the severity of COVID-19 among the vaccinated cases and breakdown of infections between adults and children.

Next steps

Israeli health officials are weighing the necessity of a third or booster dose of the vaccine. Whether they will reinstate public health measures to prevent spread of COVID-19 also remains unknown.

Going forward, Israel intends to study whether factors such as age, comorbidities, or time since immunization affect risk for breakthrough infections among people vaccinated against COVID-19.

“We want to prevent people from getting hospitalized, seriously ill, and of course, dying. It’s encouraging these vaccines will be able to have a high impact on those outcomes,” Dr. Durbin said. “We just need to get people vaccinated.”

A call for better global surveillance

A global surveillance system is a potential solution to track and respond to the growing threat of the Delta variant and other variants of concern, Scott P. Layne, MD, and Jeffery K. Taubenberger, MD, PhD, wrote in a July 7, 2021, editorial in Science Translational Medicine.

One goal, Dr. Layne said in an interview, is to highlight “the compelling need for a new global COVID-19 program of surveillance and offer a blueprint for building it.” A second aim is to promote global cooperation among key advisers and leaders in the G7, G20, and Asia-Pacific Economic Cooperation nations.

“It’s an uphill struggle with superpower discords, global warming, cybersecurity, and pandemics all competing for finite attention,” Dr. Layne said. “However, what other options do we have for taming the so-called forever virus?”

Dr. Mokdad and Dr. Jetelina had no relevant disclosures. Dr. Durban disclosed she was the site primary investigator for the phase 3 AstraZeneca vaccine trial and an investigator on the Pfizer COVID-19 vaccine trial.

A version of this article first appeared on Medscape.com.

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