2021-09-22 14:36:43 Moderna vs. Pfizer: Both Knockouts, but One Seems to Have the Edge

Moderna vs. Pfizer: Both Knockouts, but One Seems to Have the Edge

After the coronavirus vaccines were approved, federal health officials repeatedly stated, “These shots are all equally effective.”

That turned out not to be the case.

In the United States, approximately 221 million doses of the Pfizer-BioNTech vaccine have been distributed, compared to approximately 150 million doses of Moderna’s vaccine. In a half-dozen recent studies, Moderna’s vaccine appeared to be more protective in the long run than the Pfizer-BioNTech vaccine.

The Centers for Disease Control and Prevention reported on Friday that the efficacy of the Pfizer-BioNTech vaccine against hospitalization dropped from 91 percent to 77 percent after a four-month period following the second shot. During the same time period, there was no decline in the Moderna vaccine.

If the efficacy gap widens further, it may have ramifications for the booster shot debate. This week, federal agencies are assessing the need for a third dose of the Pfizer-BioNTech vaccine for some high-risk groups, including older adults.

Scientists who were initially skeptical of the reported differences between the Moderna and Pfizer-BioNTech vaccines have gradually come to believe that the difference is minor but significant.

“Our baseline assumption is that the mRNA vaccines are working similarly, but then you start to see a separation,” Natalie Dean, a biostatistician at Emory University in Atlanta, explained. “It’s not a big difference, but it’s consistent.”

However, the difference is minor, and the real-world implications are unknown, because both vaccines are still highly effective at preventing severe illness and hospitalization, she and others cautioned.

“Yes, there is most likely a significant difference, most likely reflecting what is in the two vials,” said John Moore, a virologist at Weill Cornell Medicine in New York. “How much of a difference does this really make in the real world?”

“It is not appropriate for people who took Pfizer to be upset because they received a subpar vaccine.”

Even in the initial clinical trials of the three vaccines eventually approved in the US — made by Pfizer-BioNTech, Moderna, and Johnson & Johnson — it was clear that the J.&J. vaccine was less effective than the other two. Since then, research has confirmed that trend, though J.&J. announced this week that a second dose of its vaccine increases its efficacy to levels comparable to the others.

The Pfizer-BioNTech and Moderna vaccines use the same mRNA platform, and their efficacy against symptomatic infection was remarkably similar in early clinical trials: 95% for Pfizer-BioNTech and 94% for Moderna. This was one of the reasons they were described as “more or less equivalent.”

The nuances emerged over time. Because the vaccines were never directly compared in a carefully designed study, the data indicating that effects differ are mostly based on observations.

The results of those studies can be skewed by a variety of factors, including the location, the age of the vaccinated population, when they were immunized, and the timing between doses. According to Dr. Dean

For example, the Pfizer-BioNTech vaccine was rolled out to priority groups — older adults and health care workers — weeks before Moderna’s. Immunity deteriorates more quickly in older adults, so a decline observed in a group dominated by older adults may give the false impression that the Pfizer-BioNTech vaccine’s protection deteriorates quickly.

Given these caveats, Pfizer senior vice president Dr. Bill Gruber said, “I’m not convinced that there truly is a difference.” “I don’t believe there is enough data to make that claim.”

However, the observational studies have now produced results from a variety of locations, including Qatar, the Mayo Clinic in Minnesota, and several other states in the United States, as well as in health care workers, hospitalized veterans, and the general population.

In those studies, Moderna’s efficacy against severe illness ranged from 92 to 100 percent. Pfizer-BioNTech lagged by 10 to 15 percentage points.

In terms of anti-infection efficacy, the two vaccines have diverged more sharply. Both vaccines’ effectiveness waned over time, especially after the arrival of the Delta variant, but the Pfizer-BioNTech vaccine’s values fell lower. In two recent studies, the Moderna vaccine outperformed the standard vaccine by more than 30 percentage points.

According to a few studies, the levels of antibodies produced by the Pfizer-BioNTech vaccine were one-third to one-half that of the Moderna vaccine. Dr. Moore, however, believes that the decrease is insignificant: there is a more than 100-fold difference in antibody levels between healthy people.

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Moderna vs. Pfizer: Both Knockouts, but One Seems to Have the Edge