July 8, 2021 -- Pfizer announced Thursday that it will seek 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 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.

"The vaccine is highly protective against the endpoints that matter – hospitalization and severe disease," Anna Durbin, MD, says.

"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 strong 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 says.

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, assistant professor of epidemiology, human genetics, and environmental sciences at University of Texas Science Center at Houston wrote in her Your Local Epidemiologistblog.

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 if factors such as age, pre-existing conditions or time since immunization increases the risk of breakthrough cases.

"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."