(CNN) — With a coronavirus that seems to be getting more infectious with each new strain and immunity waning over the months, the Biden administration has forecast that up to 100 million more people could get COVID-19 in the fall and winter. That estimate makes it crucial that as many people as possible get their Covid-19 booster dose, experts warn. And if you’re eligible, it’s a great time to get the second booster.
Fewer than half of eligible Americans – just a third of the entire US population – received their first booster, according to the US Centers for Disease Control and Prevention (CDC). . And only about 10 million people have taken the second extra dose, which has been approved for those 50 and older, as well as those over 12 who are moderately to severely immunosuppressed.
The CDC encourages people to stay “up to date” on their COVID-19 vaccines, including getting boosters at the right time. However, the agency still defines someone as “fully vaccinated” as having received at least the initial two-dose schedule.
Now this week, a senior Biden administration official sent a more direct message: All adults need a third vaccine.
Vaccination is the best way to protect against covid-19, and the defense is more effective with at least three vaccines, the official insisted.
Getting more Americans to get their COVID-19 booster dose could make a big difference to the number of cases, according to Dr. Peter Marks, director of the US Food and Drug Administration’s Center for Biological Evaluation and Research. USA (FDA, for its acronym in English). Marks told the American Medical Association on Monday that he is “a little worried” about the direction of the Covid-19 pandemic.
“It’s very important that we try to get half, or a little more than half, of Americans who have only gotten two doses to get that third dose,” Marks said. “That can make a difference going forward, and it can especially make a difference now that we’re entering another wave of Covid-19,” he continued.
Now, the current surge in covid-19 cases is nowhere near what the US saw with the initial wave of the omicron variant. But the country was averaging 71,577 new infections a day as of Monday, according to Johns Hopkins University.
Case rates are highest in the northeastern region of the US, where there is greater uptake of COVID-19 vaccine boosters. Nearly half the population of Vermont is fully vaccinated and has received their booster dose, along with more than 40% of the population of Maine, Rhode Island, Connecticut and Massachusetts, according to CDC data.
But cases have also started to rise in the south, where less than a quarter of the population is fully vaccinated and on booster doses. In North Carolina, Alabama, and Mississippi, fewer than 1 in 5 people have received a booster dose.
Who can get a booster shot (and who can’t)
Anyone over the age of 12 in the US can get a booster dose. But only the Pfizer/BioNTech COVID-19 vaccine is available as a booster for teens ages 12-17.
Adults who initially received an mRNA-type vaccine can get their booster dose five months after completing the initial schedule. People who have been vaccinated with Johnson & Johnson can get a booster dose two months after the first shot.
CDC data shows that the booster dose has higher uptake in older age groups in the US, consistent with broader vaccination trends. However, almost 2 in 5 people over the age of 65, and more than 3 in 5 adults in general, do not have any booster doses.
Research has shown that people who receive three doses of an mRNA-type COVID-19 vaccine have a relatively low rate of emergency room visits and COVID-19-related hospitalizations. This compared to those who only received two doses, according to the studies. Even with the more infectious omicron variant, a boost seems to protect against more severe disease.
Scientists are still trying to determine if younger people would benefit from an additional dose of the vaccine. Pfizer and BioNTech applied for an emergency use authorization for children ages 5-11.
“Hopefully this will be resolved in the not too distant future,” Marks said.
New research on fourth doses
A fourth dose of vaccines from Moderna or Pfizer/BioNTech –– which is licensed for people 50 and older in the United States–– appears safe and provides a “substantial” boost of immunity at levels similar to or even better than a third dose, according to a study published Monday.
The researchers gave study participants, whose average age was 70.1 years, either half a dose of Moderna’s vaccine or a full dose of Pfizer’s vaccine in a random selection in January, about seven months after receiving the first reinforcement. The second booster did not appear to have any significant side effects. The biggest complaints were arm pain and fatigue.
The booster also generated an immune response on day 14 that was greater than that recorded on day 28 after the third dose of Pfizer or Moderna’s COVID-19 vaccines.
When the researchers compared mRNA vaccines, Moderna’s fourth dose appeared to be slightly better than Pfizer’s, but it’s not clear why. Both generated what the scientists considered a “significant change” in protective antibodies. The T cell response also increased after the fourth dose.
Antibodies are a first line of immune protection that can stop a virus from infecting cells. T cells then intervene and destroy the infected cells. T cells cannot protect against minor infections, but they can prevent them from progressing to serious disease.
“A fourth dose of the booster vaccines against covid-19, of the mRNA type, is well tolerated and enhances cellular and humoral immunity,” says the study. “The maximal responses after the fourth dose were similar to, and possibly better than, the maximal responses after the third dose.”
The study also showed that some people who had higher levels of antibodies before the fourth dose of the vaccine had only a “limited” boost. People with a history of COVID-19 infection had a similar limited response. The authors say this suggests there may be a ceiling or maximal response that can occur with a fourth dose of the vaccine.
The study did not specifically look at neutralization of the omicron variant.
Two earlier studies conducted in Israel showed that hospitalization and death rates from Covid-19 could be reduced with a fourth dose of the vaccine given at least four months after the third. The reduction in hospitalizations and deaths persisted over time with this fourth dose.
New generation of vaccines and boosters
Marks hopes that the next generation of COVID-19 vaccines — which he predicts will arrive in a year or two — will be even better at protecting people against the full “gamut” of coronavirus variants and provide a more robust immune response.
The FDA’s vaccine advisory committee will meet in late June to review data on vaccines, including monovalents (which would target a single variant) and bivalents (which could target the parent virus strain plus another). .
“It’s a little difficult because we don’t know how much further the virus will evolve in the next few months,” Marks said. “But we don’t have a choice, because if we want to produce the hundreds of millions of doses that need to be available for a booster campaign, we have to start in early July or even earlier to get those kinds of numbers.”
The FDA committee could also debate whether an additional fall booster should be recommended for the general population or for specific groups, Marks said.
Doctors say they have heard from some patients who want to wait for their booster dose to get better winter protection. Marks said waiting to get a booster is a bad idea, especially if those people haven’t recently had COVID-19.
“Why? Because it’s going to be four, five or six months before the next reinforcement arrives,” he said. “You’re talking about having several months there at risk.”
Even with a fall and winter surge anticipated, cases are now on the rise, and those who have only received two mRNA vaccinations are vulnerable.
“Instead of being casual about it,” Marks said, “I would invite them to try to get that third dose to boost immunity, because we have a lot of Covid-19 going around.”
— CNN’s Deidre McPhillips contributed to this report.