The beginning of the vaccine rollout was a true turning point in the fight against COVID-19, especially thanks to how effective Moderna, Pfizer, and Johnson & Johnson shots were found to be against the virus. As the months have passed, however, mounting data is showing that the effectiveness of each may not hold up to the same levels over time. But in yet another pandemic twist, new research is providing experts with even more insight into why the Moderna vaccine may keep you protected from COVID-19 longer than other available shots, Axios reports.
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Experts note that while both are built using the same mRNA technology, there are two major differences between the Moderna and Pfizer vaccines in the way they are administered. The first is that the Moderna vaccine uses a much larger dosage, administering 100 micrograms (mg) of vaccine in each of the two shots compared to the 30 mg used in each shot of Pfizer. The second major difference is the longer interval between the two doses in each regimen, with Pfizer spacing them 21 days apart compared to the 28-day gap for Moderna.
One study published by the Centers for Disease Control and Prevention (CDC) on Sept. 10 highlights the stark differences. After examining more than 32,000 medical encounters from 187 hospitals and 221 emergency departments and urgent care clinics across nine states from June to Aug. 2021, researchers found that Moderna stood above the rest when it came to effectiveness—even in the face of the Delta variant. Moderna had a vaccine efficacy of 95 percent when protecting against hospitalization, while Pfizer’s vaccine was 80 percent effective and Johnson & Johnson’s was 60 percent. In terms of preventing emergency department and urgent care visits, Moderna was 92 percent effective, while Pfizer and Johnson & Johnson were 77 and 65 percent effective, respectively.
Other research has highlighted how the two mRNA vaccines generate different levels of immune response as well. A study published Aug. 30 in the Journal of the American Medical Association compared antibody response following vaccination with both Pfizer and Moderna among 2,500 health care workers from Belgium, and found that Moderna’s vaccine produces twice as many antibodies as Pfizer’s. And another study published in the journal Science on Sept. 14 compared immune responses in patients who had recovered from COVID with those who had received a 25 mg low dose of vaccine during Moderna’s clinical trial, finding that immune memory remained strong six months later even in patients aged 70 or older, even without the full 100 mg shots.
Now that enough time has passed for data on the topic to materialize, experts are beginning to note discrepancies between the two. “There have been sort of signals from enough separate sources that start to paint a picture that may reflect a real biological phenomenon—a real difference,” Natalie Dean, PhD, a professor at Emory University who specializes in vaccine study design, told Axios. “I’m starting to believe that there’s something underlying it.”
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Some experts point out that the release schedule of vaccines could also be affecting the real-world data found in the studies in question, thanks to Moderna gaining approval weeks after Pfizer. “Because of the way the rollouts happened, the oldest and most vulnerable and sickest people, like nursing home residents, got Pfizer,” John Moore, PhD, a virologist at Cornell University, told Axios.
But because of the clear discrepancy, some experts argue that the differences between the two mRNA shots should help dictate policy on boosters and who needs them most. In a series of tweets on Sept. 13, Eric Topol, MD, a cardiologist and executive vice president of Scripps Research, wrote that there was “unequivocal” evidence that there was a drop in the Pfizer vaccine’s effectiveness against hospitalizations and symptomatic infections in people 60 and older five months out from their initial doses. He argued that enough of a stark data divide exists that the vulnerable should not be left waiting for federal approval of the shots while the need for people under 60 getting a Moderna booster remained “unresolved.”
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Overall, Dean argued that time may tell whether or not vaccines will ultimately end up being similar in terms of waning efficiency. “It’s not clear that any lesson we see from Pfizer will directly translate to Moderna,” she told Axios. “I think if you asked this question a few months ago when there really [weren’t] any signals of a difference, people would very much lump them together in their mind.”
Still, others emphasized that it may not be worthwhile to engage in a head-to-head comparison between the shots when both still stand on their own merits. According to Paul Offit, MD, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia, both Pfizer and Moderna shots ultimately “do what a vaccine needs to do, which is protect against severe illness.”
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