New data presented to a Centers for Disease Control and Prevention committee provided more evidence that the Covid-19 vaccines provided robust protection against severe disease through July, after the Delta variant of the coronavirus had spread widely through the United States.
Scientists also confirmed that the Pfizer-BioNTech and Moderna shots confer a small risk of heart problems in younger men, but that the benefits still outweighed the risks.
At the committee’s meeting on Monday, Dr. Sara Oliver, a C.D.C. scientist, presented unpublished data from Covid-Net, a hospital surveillance system. All three vaccines used in the United States remained highly effective at preventing hospitalizations from April through July, when Delta became dominant, the data suggested.
For adults under the age of 75, the shots were at least 94 percent effective at preventing hospitalizations, a rate that has remained steady for months, Dr. Oliver said. Protection against hospitalization did decline in July for adults 75 or older, but still remained above 80 percent.
“Covid vaccines continue to maintain high protection against severe disease, hospitalization and death,” Dr. Oliver said.
Protection against infection or mild disease does appear to have declined somewhat in recent months, however. “These reasons for lower effectiveness likely include both waning over time and the Delta variant,” she said.
The data comes in the midst of an ongoing debate about the necessity and timing of booster doses. On Aug. 18, health officials recommended that adults who received either the Pfizer or Moderna vaccines get a third shot eight months after their second dose. If the F.D.A. clears the booster shots, they will be available beginning Sept. 20, top federal health officials have said.
The recommendation was based on data suggesting that the vaccines may become less effective at protecting against infection and mild disease over time. But the shots still work well against severe disease and death, and many scientists have criticized the plan for booster shots, saying that it’s not yet clear that they’re needed.
The C.D.C. advisory committee will review additional data on the safety, effectiveness and potential need for booster doses at a meeting in September.
However, getting shots to unvaccinated people should continue to be the top priority, Dr. Oliver said: “Planning for delivery of booster doses to vaccinated individuals should not deter outreach for delivery of primary series to unvaccinated individuals.”
Understand Vaccine and Mask Mandates in the U.S.
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- Vaccine rules. On Aug. 23, the Food and Drug Administration granted full approval to Pfizer-BioNTech’s coronavirus vaccine for people 16 and up, paving the way for an increase in mandates in both the public and private sectors. Private companies have been increasingly mandating vaccines for employees. Such mandates are legally allowed and have been upheld in court challenges.
- Mask rules. The Centers for Disease Control and Prevention in July recommended that all Americans, regardless of vaccination status, wear masks in indoor public places within areas experiencing outbreaks, a reversal of the guidance it offered in May. See where the C.D.C. guidance would apply, and where states have instituted their own mask policies. The battle over masks has become contentious in some states, with some local leaders defying state bans.
- College and universities. More than 400 colleges and universities are requiring students to be vaccinated against Covid-19. Almost all are in states that voted for President Biden.
- Schools. Both California and New York City have introduced vaccine mandates for education staff. A survey released in August found that many American parents of school-age children are opposed to mandated vaccines for students, but were more supportive of mask mandates for students, teachers and staff members who do not have their shots.
- Hospitals and medical centers. Many hospitals and major health systems are requiring employees to get a Covid-19 vaccine, citing rising caseloads fueled by the Delta variant and stubbornly low vaccination rates in their communities, even within their work force.
- New York City. Proof of vaccination is required of workers and customers for indoor dining, gyms, performances and other indoor situations, although enforcement does not begin until Sept. 13. Teachers and other education workers in the city’s vast school system will need to have at least one vaccine dose by Sept. 27, without the option of weekly testing. City hospital workers must also get a vaccine or be subjected to weekly testing. Similar rules are in place for New York State employees.
- At the federal level. The Pentagon announced that it would seek to make coronavirus vaccinations mandatory for the country’s 1.3 million active-duty troops “no later” than the middle of September. President Biden announced that all civilian federal employees would have to be vaccinated against the coronavirus or submit to regular testing, social distancing, mask requirements and restrictions on most travel.
The committee unanimously voted to recommend the Pfizer-BioNTech vaccine, which was approved by the Food and Drug Administration last week, for Americans 16 or older.
Scientists also presented to the committee new data on the risks of two heart conditions following vaccination: myocarditis, an inflammation of the heart muscle, and pericarditis, an inflammation of the membrane that surrounds the heart.
The side effects tend to be mild, temporary, and uncommon, the data confirmed. For every million doses of the second shot given to 12- to 39-year-olds, there were 14 to 20 extra cases of the heart problems, according to the new data, which was presented Monday at a meeting of an independent advisory committee to the C.D.C.
“The data suggest an association of myocarditis with mRNA vaccination in adolescents and young adults,” Dr. Grace Lee, a pediatrician at Stanford and chair of the committee, said at the meeting on Monday. “Further data are being compiled to understand potential risk factors, optimal management strategies and long-term outcomes.”
But the benefits of the vaccines are substantial, even for those in the highest risk groups. According to an analysis presented by a C.D.C. scientist on Monday, every million doses of the Pfizer vaccine administered to 16- and 17-year-old boys would be expected to cause 73 cases of the heart problems, while preventing more than 56,000 Covid-19 cases and 500 related hospitalizations.
A study published in the New England Journal of Medicine last week reported that the risk of myocarditis was substantially higher after infection with the virus than after vaccination.