Pfizer, Moderna Vaccines Still Offer Good Protection Against Severe COVID: Study

FRIDAY, Sept. 17, 2021 (HealthDay News) -- With a special advisory panel to the U.S. Food and Drug Administration meeting Friday to decide on the need for COVID vaccine booster shots, new data shows Pfizer-BioNTech and Moderna vaccines maintaining strong levels of protection against severe illness.

The data tracked the cases of nearly 3,700 American adults cared for at 21 hospitals across the nation from March 11 to Aug. 15, 2021 -- a time span that dovetails with the emergence and dominance of the highly contagious Delta variant.

Nearly half (about 46%) were admitted with COVID-like illness and later tested positive for the new coronavirus; the rest did not have COVID.

Comparing the patients' vaccination histories, a team led by Dr. Wesley Self of Vanderbilt University Medical Center in Nashville, Tenn., wrote that "vaccine effectiveness against COVID-19 hospitalizations was higher for the Moderna vaccine" at 93%. Effectiveness of the Pfizer vaccine came in slightly lower at 88%.

Both of the two-dose mRNA-based regimens beat the effectiveness of the one-dose Johnson & Johnson vaccine, which maintained 71% effectiveness in warding off a case of COVID-19 so severe that it would require hospitalization.

There was some sobering news for folks who got the Pfizer shot: "Protection for the Pfizer-BioNTech vaccine declined 4 months after vaccination," Self's group noted, although it still remained high.

No such decline in effectiveness was seen for people who got the Moderna shots.

Another arm of the study looked at levels of antibodies to the new coronavirus in 100 healthy volunteers. Samples were taken two to six weeks after they had gotten fully vaccinated with any of the three vaccines.

The result: Antibody levels "were significantly lower in persons vaccinated with the Janssen [J&J] vaccine than the Moderna or Pfizer-BioNTech vaccines," the researchers reported.

The Moderna vaccine also produced higher "antibody levels than did the Pfizer-BioNTech vaccine," the researchers said.

They suspect that could be because of higher levels of protective mRNA in the Moderna vaccine than in the Pfizer shot, or because people who got the Moderna shot typically received their second dose slightly later than people who received the Pfizer regimen (four weeks versus three weeks, respectively).

However, according to the research team, the takeaway is clear: "All FDA-approved or [emergency]-authorized COVID-19 vaccines provide substantial protection against COVID-19 hospitalization."

Self's team stressed that the study had some limitations.

First, assessment of the J&J vaccine is hampered because relatively fewer Americans received that shot compared to the many tens of millions who received the two-dose vaccines.

And although the study occurred during the time that the Delta variant became dominant in the United States, researchers did not examine each vaccine's effectiveness against it specifically.

The findings were published Sept. 17 in Morbidity and Mortality Weekly Report, a journal of the U.S. Centers for Disease Control and Prevention.

The new data will surely be part of deliberations by an FDA advisory committee convened Friday to decide whether third "booster" shots are necessary for the average American. (Third shots have already been approved for people with compromised immune systems).

While today's new data suggest that vaccine-induced immunity remains high against severe COVID, data from Israel suggests boosters could be helpful. Israel began offering boosters to its citizens this summer.

In the Israeli study, published Sept. 15 in the New England Journal of Medicine, more than 1 million people aged 60 and older got a third dose. The data show they were much less likely to become infected soon after with the contagious Delta variant, according to the Associated Press, achieving what Pfizer called "roughly 95% effectiveness." It is not known how long that protection will last.

However, FDA reviewers have suggested they would primarily focus not on the Israeli data but on how vaccines have worked among Americans, which they said "may most accurately represent vaccine effectiveness in the U.S. population."

Pfizer, meanwhile, has indicated that its vaccine is protecting against severe disease in the United States, but immunity against milder infections wanes around six to eight months after the second dose.

Pfizer gave third doses to 306 individuals and found their antibodies were three times higher than after earlier doses, the AP reported. The company said the antibodies appeared strong enough to be effective for the Delta variant.

The need for booster shots has become a contentious issue in recent weeks, after President Joe Biden announced a booster campaign that was slated to begin Sept. 20. Soon after that announcement two top FDA vaccine regulators joined with international scientists to release a report contending that boosters are not needed for healthy individuals, because the vaccines continue to offer strong protection from severe disease.

Although the FDA is not bound to follow the advice of its advisory committees, it typically does so.

More information

Find out more about the effectiveness of COVID-19 vaccines at the U.S. Centers for Disease Control and Prevention.

SOURCES: U.S. Centers for Disease Control and Prevention, Morbidity and Mortality Weekly Report, Sept. 17, 2021; Associated Press, Sept. 16, 2021