(CNN)The protection provided by Covid-19 vaccines appears to wane over time, especially for people 65 and older, a US Centers for Disease Control and Prevention expert said Wednesday.
Ruth Link-Gelles, who helps lead the CDC’s Vaccine Effectiveness Team, reviewed a series of studies looking at the overall effectiveness of vaccines in various groups between February and August and found similar patterns for Pfizer’s and Moderna’s vaccines, both made using mRNA.
The findings tended to support the argument that people’s protection starts to wane after a few months, and that boosters might help restore their immunity.
Effectiveness started to wane a few months after people were fully vaccinated — defined as two weeks after their second dose of either vaccine.
“For individuals 65 plus, we saw significant declines in VE (vaccine effectiveness) against infection during Delta for the mRNA products,” Link-Gelles told the a meeting of CDC vaccine advisers.
The CDC’s Advisory Committee on Immunization Practices met Wednesday to discuss the potential need for booster doses of vaccines.
Later Wednesday, the US Food and Drug Administration issued an emergency use authorization to Pfizer for boosters in people 65 and older, those with underlying conditions putting them at high risk of severe disease, and for people whose jobs put them at high risk of exposure.
ACIP will reconvene Thursday to discuss the FDA’s EUA and will issue its own recommendations about how it should be applied to the US population. The CDC director must then sign off on these recommendations. They currently will only apply to Pfizer’s vaccine.
One study called SUPERNOVA looked at veterans between February and August of this year. In that study, the Pfizer vaccine provided 92% protection against hospitalization for those ages 18 to 64, and 77% for those over 65, Link-Gelles said. The Moderna vaccine provided 97% protection against hospitalization for those 18-64, and 87% for those 65 and older. Effectiveness did not seem to be affected by the arrival of the Delta variant, the study found.
A study called IVY looked at hospitalized adults in 18 states between March and August. Efficacy of Pfizer’s vaccine waned from 91% 14 to 120 days after full vaccination, to 77% three months or more after full vaccination. Moderna’s vaccine effectiveness did not really wane, staying at 92% or 93% in that study.
In a study of 4,000 health care personnel, first responders, and other frontline workers in eight places who were tested every week regardless of symptoms, vaccine protection against any infection declined from 91% pre-Delta to 66% during Delta.
Pfizer told ACIP it hopes and expects that antibody protection from a third dose of its Covid-19 vaccine will last longer than after the initial two doses, but more research will be needed to determine whether more doses would be needed later on.
The conversation for now is focused on a third dose — a booster — of the company’s two-dose Covid-19 vaccine, and experience with past vaccines suggests a third dose may provide longer, stronger protection, Pfizer Senior Vice President Dr. William Gruber told the committee. In that case, the primary series of the vaccine may work better as three doses, Gruber noted. But, he acknowledged, some experts believe protection is likely to drop again after a third booster dose.
“I think this is going to be driven largely by what we find in retrospect as we gather more information about protection, and we just need to stay tuned,” Gruber said.
Gruber also said the company will continue to explore whether a longer interval between vaccine doses would work better; currently, the recommendation is 21 days between a first and second dose. He noted researchers in Europe and elsewhere have studied longer intervals, but the company’s focus has been maximizing protection as quickly as possible during the pandemic.
“We’ll continue to explore whether or not it makes some sense to look at a longer interval,” Gruber said.
Pfizer is not studying using its vaccine as a booster for the Moderna or Johnson & Johnson vaccines, Gruber said, but it welcomes studies by others. Members of the committee asked whether that was something worth discussing.
The FDA’s Dr. Doran Fink said there is no data on the safety or efficacy of mixing and matching vaccines – boosting with a dose of a brand of vaccine that is different from that used for the original immunization.
Moderna has asked the FDA to approve booster shots for its vaccine, but the FDA so far has only considered Pfizer’s bid. Johnson & Johnson released partial data this week that it said showed a booster dose greatly raised immunity, but the company has not yet applied with the FDA to consider a booster vaccine dose.
ACIP members said they worried people may mistake the talk of boosters as a signal that Covid-19 vaccines don’t work well. They agreed that would be a mistaken impression, and one that public health specialists would need to fight against.
But people also need to understand that coronavirus vaccines could never completely defeat this virus.
“Coronaviruses often become endemic, and it is highly unlikely that we will prevent all mild or symptomatic respiratory infection,” ACIP member Dr. Helen Keipp Talbot of Vanderbilt University told the meeting.
“One of the things that we need to begin to understand is that we will likely prevent hospitalizations and deaths, and hopefully symptomatic lower respiratory infections, but it is unlikely that we will prevent everything,”
The panel also heard about studies of the safety of Covid-19 vaccines in pregnant women.
“It has been incredibly reassuring to date,” Dr. Grace Lee, a professor of pediatrics at Stanford University School of Medicine and chair of ACIP, told the meeting.
So far, there’s no evidence that getting vaccinated during pregnancy raises the risk of miscarriage or birth defects, several experts told the meeting. Yet just 30% of pregnant women in the US have been vaccinated against coronavirus — even as Covid-19 is killing more pregnant women than ever before, the advisers heard.
And pregnant people have a higher risk than most of severe disease if they catch coronavirus, Dr. Dana Meaney Delman, the CDC’s lead on maternal immunization, told the meeting.
“We now see increased numbers of pregnant people admitted to the ICU in July and August,” Meaney Delman told the meeting. The trend has continued into September, she said. “The deaths reported in August is the highest number of deaths reported in any month since the start of the pandemic,” Meaney Delman added. About 97% of the pregnant people treated in the hospital for Covid-19 have been unvaccinated, she said.
Get CNN Health’s weekly newsletter
“I want to speak directly to the public,” Meaney Delman added. “We know that pregnant people with Covid-19 can become very sick. Some will die, and many will experience pregnancy and neonatal complications,” she said.
“We know that because of Covid some children will grow up without their mothers. We know that Covid-19 vaccines are safe and effective. If you are pregnant, postpartum, breastfeeding, trying to get pregnant now or might become pregnant in the future, please get vaccinated.”