Delta Variant Key to Breakthrough Infections in Vaccinated Israelis

Damian McNamara

July 07, 2021

Updated July 8, 7:15 pm // This story has been updated to show that Pfizer will seek an FDA EUA for a booster to its COVID vaccine prompted by new data from Israel.

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

Pfizer announced Thursday that it will seek US Food and Drug Administration (FDA) authorization for a booster shot of its COVID-19 vaccine as the company acknowledges its two-dose vaccine has shown waning effectiveness against the Delta variant.

In a statement, the company said it will seek an emergency use authorization in August and will release more data first, CNN reported.

"As seen in real world data released from the Israel Ministry of Health, vaccine efficacy in preventing both infection and symptomatic disease has declined six months post-vaccination, although efficacy in preventing serious illnesses remains high," the statement said, according to multiple news outlets.

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

The country's Ministry of Health data shows high levels of circulating Delta variant and a relaxation of public health measures in early June led to a drop in the vaccine's prevention of "breakthrough" cases from 94% to 64% in recent weeks.

"While protection against severe disease remained high across the full six months, a decline in efficacy against symptomatic disease over time and the continued emergence of variants are expected," Pfizer's statement said. "Based on the totality of the data they have to date, Pfizer and BioNTech believe that a third dose may be beneficial within 6 to 12 months following the second dose to maintain highest levels of protection."

Still, it is important to consider the findings in context, experts say.

"My overall take on this is that the vaccine is highly protective against the endpoints that matter — hospitalization and severe disease," Anna Durbin, MD, told Medscape Medical News.

"I was very pleasantly surprised with the very high efficacy against hospitalization and severe disease — even against the Delta variant," added Durbin, professor of medicine, at Johns Hopkins Bloomberg School of Public Health in Baltimore.

Ali Mokdad, PhD, of the Institute for Health Metrics at the University of Washington in 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 told Medscape Medical News.

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

Dr Ali Mokdad

"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 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, 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 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, 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,' " 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.

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," 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 editorial in Science Translational Medicine.

Dr Scott Layne

One goal, Layne told Medscape Medical News, 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, added Layne

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

Mokdad and Jetelina have disclosed no relevant financial relationships. Durban disclosed she was the site PI for the Phase 3 AstraZeneca vaccine trial and an investigator on the Pfizer COVID-19 vaccine trial.

Damian McNamara is a staff journalist based in Miami. He covers a wide range of medical specialties, including infectious diseases, gastroenterology and neurology. Follow Damian on Twitter: @MedReporter.

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