RELATED: If You Did This After Your First Shot, You’re at Risk for the Delta Variant. On July 8, Pfizer cited data from a study out of Israel and said its vaccine’s efficacy “in preventing both infection and symptomatic disease has declined six months post-vaccination.” The Israel study, published three days prior, had concluded that the Pfizer vaccine was 64 percent effective at preventing infection from the Delta variant, down from 94 percent, The Wall Street Journal reported. The vaccine still proved to be highly effective at preventing severe illness at 94 percent, down from 97 percent, per Israel’s Health Ministry. But while Pfizer believes this data is reason enough to move forward with a third dose of its vaccine within six to 12 months of vaccination, the FDA and CDC are not yet convinced. In their joint statement, also released July 8, the agencies clearly stated, “Americans who have been fully vaccinated do not need a booster shot at this time.” They reiterated that the existing COVID vaccines are highly effective at preventing severe disease and death, even in the face of the Delta variant. If the FDA and CDC don’t agree with Pfizer’s urgency, however, when do they believe COVID boosters will be necessary? There is no clear answer from the agencies yet, although the joint statement did stress that they are “engaged in a science-based, rigorous process to consider whether or when a booster might be necessary.” Meanwhile, experts have offered their insight into what needs to happen before you get a third shot. RELATED: For more up-to-date information, sign up for our daily newsletter. The question of boosters came up in the CDC’s Advisory Committee on Immunization Practices (ACIP) meeting in June, CNN reported. ACIP member Sarah Long, MD, said there are two things the committee would need to see before they believed it was time for people to get another shot. “What we are looking for is both a very careful look at breakthrough cases and also whether there is currently an uptick in the elderly—that would be pretty clear because they are currently so well controlled,” Long said. ACIP member Sharon Frey, MD, shared a similar sentiment at the June meeting. “I think the only thing we can do at this moment is, if we start to see an uptick in reinfections in people, or new infections in people who have been vaccinated, that’s our clue that we need to move quickly,” she said, per CNN.ae0fcc31ae342fd3a1346ebb1f342fcb The timeline is still uncertain, but these vaccine experts agree that if there’s a rise in breakthrough cases, that’s when you will need a COVID booster shot. William Schaffner, MD, professor at Vanderbilt University School of Medicine and medical director of the National Foundation for Infectious Diseases, told CNN that we don’t currently need boosters, but he also pointed to vulnerable populations, like the 2 to 4 percent of the U.S. population that is immunocompromised. This group might need another shot sooner given their diminished response to the initial vaccine. Until there is enough of a rise in breakthrough cases to make U.S. agencies feel compelled to approve a COVID booster, you might feel anxious about your current vaccination status. Most experts, however, say there’s no cause for alarm. “Pfizer says we may need a booster. Call me skeptical,” Ashish K. Jha, MD, dean of the Brown University School of Public Health, tweeted on July 8. While there has been some data that antibody levels decrease over time, “immunity is far more complex. And there is plenty of data that 2-shot regimen working well.” RELATED: Vaccinated People Who Get COVID Have These 3 Things in Common, Study Shows.