People who were not fully vaccinated this spring and summer were more than 10 times more likely to be hospitalized, and 11 times more likely to die of covid-19, than those who were fully vaccinated, according to one of three major studies published Friday by the Centers for Disease Control and Prevention that highlight the continued efficacy of all three vaccines amid the spread of the highly contagious delta variant.
A second study showed that the Moderna coronavirus vaccine was more effective in preventing hospitalizations than its counterparts from Pfizer-BioNTech and Johnson & Johnson. That assessment was based on the largest U.S. study to date of the real-world effectiveness of all three vaccines, involving about 32,000 patients seen in hospitals, emergency departments and urgent-care clinics across nine states from June through early August.
While the three vaccines were collectively 86 percent effective in preventing hospitalization, protection was significantly higher among Moderna vaccine recipients (95 percent) than among those who got Pfizer-BioNTech (80 percent) or Johnson & Johnson (60 percent). That finding echoes a smaller study by the Mayo Clinic Health System in August, not yet peer-reviewed, which showed the Moderna vaccine to be more effective than Pfizer-BioNTech at preventing infections during the delta wave.
Noting the effectiveness of all vaccines against severe illness and death, public health officials have continued to urge people to get whatever vaccine is available, rather than to shop around and delay inoculation.
“The bottom line is this: We have the scientific tools we need to turn the corner on this pandemic,” CDC Director Rochelle Walensky said at a White House coronavirus briefing Friday. “Vaccination works and will protect us from the severe complications of covid-19.”
The trio of reports comes just after President Biden announced sweeping coronavirus vaccine mandates Thursday to curb the surging delta variant, a move expected to increase the pressure on the tens of millions of Americans who have resisted vaccinations. The virus has killed more than 650,000 people in the United States, with about 1,500 average daily deaths for the past eight days — a toll not seen since early March, according to data analyzed by The Washington Post.
The CDC studies offer some clarity at a confusing moment in the pandemic amid concerns about waning immunity and the vaccines’ protection against a more contagious variant. The data is broadly consistent with findings from other studies: The vaccines continue to provide strong protection for most people against hospitalization and death, even during the delta surge, but are less effective in protecting the oldest adults, especially those with underlying medical conditions.
The highly transmissible delta variant now accounts for more than than 99 percent of new coronavirus infections, the CDC estimates. Fear of fading protection against severe disease is why the administration hopes to roll out boosters as soon as health authorities give the green light. Pfizer is in line to be the first brand approved as a booster by the Food and Drug Administration, since the company has submitted data on the safety and effectiveness of boosting its own two-shot regimen with a third shot of the same vaccine. Approval of the other vaccines is expected to follow in coming months.
In the CDC report that analyzed vaccine effectiveness by brand, researchers looked at how well the shots protected against severe disease. They measured effectiveness against hospitalization and, separately, against trips to the emergency department or urgent care. Overall effectiveness in preventing
emergency department or urgent-care trips was 82 percent. Effectiveness was highest among Moderna recipients (92 percent), followed by Pfizer (77 percent) and Johnson & Johnson (65 percent).
The CDC report doesn’t explain why Moderna might offer a greater benefit. One possibility is that Moderna’s dose of mRNA is three times that of Pfizer-BioNTech’s. The interval between shots is also longer: four weeks for Moderna instead of three weeks for Pfizer-BioNTech. Some research has shown that longer intervals between shots — including much longer periods, beyond four weeks — could be advantageous to building immunity.