CLEVELAND — Researchers from Case Western Reserve University School of Medicine have found some advantages for those who received the Moderna vaccine, compared to the Pfizer-BioNTech vaccine, when it comes to the Delta variant.

That study was published Thursday in the Journal of the American Medical Association, titled "Comparison of mRNA-1273 and BNT162b2 Vaccines on Breakthrough SARS-CoV-2 Infections, Hospitalizations, and Death During the Delta-Predominant Period."

Researchers analyzed electronic health records from more than 637,000 fully vaccinated patients (identified as people who had received two vaccine shots) from 63 healthcare organizations across the United States.

The data came from July through November 2021, a period during which Delta variant dominated, and the study excluded people with previous COVID-19 infections, as well as those who had already received a booster shot.

The results

“We looked at people who were fully vaccinated, according to the CDC definition, which was two shots at the appropriate interval. No booster,” said Dr. Pamela Davis, the Arline and Curtis Garvin Professor in The Center for Community Health Integration at Case Western Reserve University and one of the study’s co-authors.

“We were pleased to see that the vaccine was so effective in the first place, but we were also pleased to see that we can detect differences,” Davis said.

Davis said at first, the data appeared to show people who were sicker were those who had received the Moderna vaccine, rather than the Pfizer one. However, after adjusting for factors such as age, sex, race, and other illnesses that were known risk factors for COVID-19 infection, that was no longer the case.

Rong Xu, Ph.D., professor of Biomedical Informatics at Case Western Reserve University School of Medicine, was the study’s main author. She noted that “among infected people, Moderna vaccine recipients, they are also less likely to be hospitalized, compared to people who received the Pfizer vaccine.”

The data showed that Moderna vaccine recipients had fewer breakthrough infections and hospitalizations than did Pfizer recipients.

Overall, the researchers emphasized that despite the difference in breakthrough infections and hospitalizations, the two vaccines showed no “statistically significant” difference in mortality rates, probably because in these vaccinated patients, death was a rare occurrence.

'Both vaccines are very, very good'

Dr. Amy Edwards, a pediatric infectious disease specialist at University Hospitals, agreed with the researchers, saying it’s not surprising Moderna was a little more effective since it contains a higher amount of mRNA per dose. She noted she has talked to people previously vaccinated with Pfizer who opted for a Moderna booster to get that higher dose.

“For anybody under the age of 18, they don't have a choice. Pfizer is the only vaccine available,” Edwards said. “We'd have to wait for more data for those younger people. But I think overall, the data is not shocking to anybody.”

Edwards noted that she, like the researchers, would conclude from this study that “both vaccines are very, very good.”

For the majority of the population, “young, healthy people who are at low risk anyways, I think this just shows that it probably doesn't matter which vaccine that you get. Certainly, if you're higher-risk, would you maybe want that extra smidge of protection that Moderna gave?” Edwards said.

'Not in the Delta phrase anymore'

Edwards and the researchers all cautioned that these results, which focused on Delta, don’t tell us about Omicron.

“There is a higher risk of being in the hospital from Delta if you have had the Pfizer vaccine, but we're not in the Delta phase anymore,” Davis said.

Still, Davis said this gives both the public and physicians more information to consider.

“Although there have been a lot of rumors and anecdotal information, I think it's important to go to real data in real people,” Davis said.

She added that “the availability of databases that are updated in real-time has been very valuable in drawing conclusions about this pandemic, and I think that the electronic health records and many other things that go online very quickly, the data from the CDC about the prevalence in the community, is just a very helpful adjunct to understanding this pandemic.”

The researchers hope to do a follow-up study to see if the vaccines showed any differences in omicron patients.

Edwards said she believes it would be interesting to repeat this study in the light of Omicron, which descended from a different variant than Delta, and understand why there are so many more breakthrough cases of Omicron.

But she acknowledged that would likely be difficult.

“So many more people have boosters now than used to, and so the study would start to get a lot more complicated because you'd have to account for when they got their booster dose and which vaccine they got boosted,” Edwards said. “Because a lot of people just got boosted with whatever, they weren't necessarily matching up to their primary shots, and so it could get a lot more complicated.”

Olivia Fecteau is a reporter at News 5 Cleveland. Follow her on Facebook and Twitter.

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