After finally getting vaccinated, you may have felt like your days of worrying about catching COVID were behind you. Unfortunately, the Delta variant has complicated things. As the more contagious strain of the virus—now dominant in the U.S.—continues to spread far and wide, vaccinated people are worried about the potential for breakthrough COVID infections. And while the vast majority of these cases are thankfully mild, one recent study found that those who got the Pfizer vaccine may be even less protected from breakthrough Delta variant infections than expected.
A preprint study conducted by nfrence and the Mayo Clinic found that Pfizer's effectiveness dropped substantially when up against the Delta variant. The Aug. 8 study concluded that the vaccine was only 42 percent effective against the virus in July when Delta was the dominant variant. This is a significant drop in protection for a vaccine whose efficacy was 95 percent in clinical trials. "If that's not a wakeup call, I don't know what is," a senior Biden official told Axios.
The study set out to compare the effectiveness of the two mRNA vaccines, Pfizer and Moderna. The data was compiled via the Mayo Clinic Health System through the months of January to July. Initially, the study found that the Moderna vaccine was 86 percent effective against infection while Pfizer was 76 percent effective against infection. And the vaccines were more protective against hospitalization and severe disease. Moderna's vaccine was 92 percent effective against hospitalization, and Pfizer's was 85 percent effective.
But both vaccines saw a significant drop in effectiveness when the Delta variant became more prevalent in July. During that month, Moderna was 76 percent effective against infection, while Pfizer was only 42 percent effective. "Based on the data that we have so far, it is a combination of [two] factors," study lead author Venky Soundararajan, PhD, told Axios. "The Moderna vaccine is likely—very likely—more effective than the Pfizer vaccine in areas where Delta is the dominant strain, and the Pfizer vaccine appears to have a lower durability of effectiveness."
While this data is concerning, Axios notes that there has yet to be data that shows either vaccine's protection against severe disease or death is significantly diminished in the face of the Delta variant. Experts caution the public not to panic about these findings before more research is done. "This is the kind of surprising finding that needs confirmation before we should accept its validity," Cornell virologist John Moore, PhD, told Axios.
Pfizer said in a statement to Axios that the company expects "to be able to develop and produce a tailor-made vaccine against that variant in approximately 100 days after a decision to do so, subject to regulatory approval." On July 28, Pfizer shared data that found that a booster shot of its vaccine could afford protection beyond what the standard two doses create.
The data suggested that people aged 18 to 55 who get a third dose see their antibody levels against the Delta variant rise more than five-fold from what they were after the second dose. Meanwhile, people aged 65 to 85 experienced an 11-fold increase in antibodies. Researchers wrote that there's "estimated potential for up to 100-fold increase in Delta neutralization post-dose three compared to pre-dose three."
During the Forbes Health in Action Summit on June 8, Moderna CEO Stéphane Bancel acknowledged that the current two-dose regimen might not be enough to protect people long-term, especially as new variants emerge. Bancel predicted that Moderna booster shots would begin sometime in the fall or winter.
"I think for next fall, we as a community should rather be two months too early boosting than two months too late. And there is no way to precisely know when people should be boosted," Bancel said. "Given we are all evolving with very uncertain data with a brand-new virus, I think being cautious and boosting early is going to be wise for that pandemic phase in the boosting phase of 2022 or late 2021."