The effectiveness of the two most widely used COVID-19 vaccines in the United States dropped significantly in July, a new study found.
The efficacy of shots from Moderna and Pfizer were highly effective in preventing transmission of the CCP (Chinese Communist Party) virus, which causes COVID-19, between January and June, researchers with the Mayo Clinic and Massachusetts-based nference discovered.
But the efficacy of Moderna’s jab dropped to 76 percent in July, with Pfizer’s plummeting to 42 percent, researchers said.
The scientists studied health records from the Mayo Clinic to determine the effectiveness in an observational study that was recently published online (pdf) but has not yet been peer reviewed.
At the same time the drop in effectiveness was seen, the Delta variant of the CCP virus became much more prevalent in Minnesota, researchers noted, comprising over 70 percent of the cases in the state.
The researchers also found that alongside the drop in transmission protection, the vaccines remained highly effective against hospitalization.
“Our observational study suggests that while both mRNA COVID-19 vaccines strongly protect against infection and severe disease, there are differences in their real-world effectiveness relative to each other and relative to prior months of the pandemic. Larger studies with more diverse populations are warranted to guide critical pending public and global health decisions, such as the optimal timing for booster doses and which vaccines should be administered to individuals who have not yet received one dose,” they wrote.
Pfizer and Moderna did not respond to requests for comment. Their vaccines are the most widely administered in the United States. Only one other is authorized for emergency use in the country.
The companies recently reported waning effectiveness for the vaccines against transmission, with Moderna’s dropping to 93 percent efficacy after six months and Pfizer’s declining to 84 percent effectiveness.
But other recent studies suggest the possibility of a much lower efficacy, particularly for Pfizer’s jab.
The effectiveness was higher in other research, including a paper published in the New England Journal of Medicine that found Pfizer’s shot was 88 percent effective against the Delta variant.
The recent studies taken together point to an estimate of 50- to 60 percent effectiveness in mRNA vaccines against symptomatic infection, according to Eric Topol, director and founder of the Scripps Research Translational Institute.
“There needs to be truth-telling about the reduced protection of mRNA vaccines vs symptomatic Delta infections,” he wrote on Twitter. “Why is this important? Because we need to protect the protected, the fully vaccinated. Sure we want to get more people vaccinated, but truth engenders trust. And truth helps guide people to be safe, use masks, distance, ventilation and all the other tools we have and know helps.”
The waning effectiveness prompted Dr. Rochelle Walensky, the director of the Centers for Disease Control and Prevention (CDC), to declare last week that vaccines no longer prevent transmission at all.
“Our vaccines are working exceptionally well. They continue to work well for Delta with regard to severe illness and death, they prevent it. But what they can’t do any more is prevent transmission,” she said on CNN.
The agency didn’t respond to a query regarding what Walensky meant, since its official website says vaccines remain effective in preventing transmission, though not 100 percent effective, and with lower efficacy against the Delta variant.
U.S. officials are also considering advising certain populations to get a booster shot.
The Food and Drug Administration is reportedly set as soon as Thursday to authorize extra COVID-19 vaccine doses, ahead of an Aug. 13 CDC advisory panel meeting that will discuss whether the boosters are required.
The panel weighed last month whether to recommend boosters, but ultimately decided against making a recommendation at that time.