US COVID-19 vaccine booster drive slows, with 85 million eligible Americans still without their extra shot

With the highly infectious omicron COVID-19 variant spreading rapidly across the country and overwhelming the health care system, health officials have been pleading with Americans to get vaccinated and boosted.

"The doctors and data have made crystal clear, vaccinations and boosters provide the best protection," White House COVID-19 coordinator Jeff Zients said during a press briefing on Wednesday. "Vaccines remain our single most powerful tool."

But despite continued public urgings from the White House and the Centers for Disease Control and Prevention, the nation's vaccination initiation and COVID-19 booster rate continues to lag, which experts say is particularly worrisome, as efficacy continues to wane overtime.

"Booster shots are effective against both infection and serious disease," Dr. David Dowdy, an infectious disease epidemiologist at Johns Hopkins Bloomberg School of Public Health, told ABC News. "If people don't get boosted, we as a population are more vulnerable to the virus. To my mind, the biggest concern is that people who are vaccinated but not boosted may infect people who haven't been vaccinated."

As of Wednesday, just under half of those who are eligible to receive a booster -- about 85 million Americans -- have yet to receive their additional shot, and data shows that each day, fewer and fewer Americans are getting vaccinated. Since mid-December, the number of Americans receiving their booster every day has been cut in half -- falling from more than 1 million people boosted every day to just over half a million people. In addition, 63 million eligible Americans remain totally unvaccinated.

Experts say several factors are to blame for the nation's drop in booster shots being administered, including confusion with the CDC's messaging and an uncertainty and lack of understanding from many about the urgency and need for boosters.

Last week, CDC Director Dr. Rochelle Walensky shared three new studies, all of which clearly demonstrated that unvaccinated individuals are at greater risk of severe illness, and even death, from COVID-19, compared to those who are vaccinated. The studies found that booster shots significantly increased protection against severe disease, both during the delta wave and at the beginning of the omicron wave.

"Protection against infection and hospitalization with the omicron variant is highest for those who are up to date with their vaccination, meaning those who are boosted when they're eligible. There are still millions of people who are eligible for booster doses and have not yet received one," Walensky said during a White House COVID-19 press briefing last week.

The first study found a third shot slashed the risk of visiting the ER or urgent care by 94% during delta and 82% during omicron. A second study found that the unvaccinated were nearly 14 times more likely to be infected and 53 times more likely to die, compared to the vaccinated and boosted, and a third study reported that although omicron was more likely to cause breakthrough infections compared to delta, even among the boosted, protection against more severe illness remained high.

"There may be a bit more pain and suffering with hospitalizations in those areas of the country that have not been fully vaccinated or have not gotten boosters," Dr. Anthony Fauci told Martha Raddatz during an appearance on ABC News' "This Week" on Sunday.

Messaging on vaccinations cause confusion

Health experts suggest the nation's slowing booster campaign and the CDC's unclear messaging and guidance are the reasons many Americans haven't felt the need to get boosted.

"While the initial vaccination drive was met with clear communications, incentives and mandates, the booster campaign has had far less organization," said John Brownstein, Ph.D., an epidemiologist at Boston Children's Hospital and an ABC News contributor.

Complicating matters is the fact that the virus has already mutated several times, with new variants emerging, creating additional confusion.

"The changing science of variants and boosters has required real-time adapting of public health messaging and guidance, providing less time to prepare and convince people on the value of a third shot," Brownstein said.

Further muddling the messaging is the discussion about whether a fourth dose of a coronavirus vaccine shot will be needed to offer protection against omicron. Israel is currently administering additional boosters to residents over the age of 60, and immunocompromised individuals, among others.

When asked whether a fourth shot will be necessary, Fauci told ABC's "This Week" that it is still unclear whether an additional booster shot will be recommended, as scientists are still trying to determine how much protection is provided by the first booster.

Fauci added that it's "quite conceivable, and I hope it's true, that the third shot boost will give a much greater durability of protection."

Some Americans may not understand the urgency for boosters, experts say

Although researchers report that the science behind the benefit of boosters is clear, some experts say many Americans still do not fully understand the urgency of getting boosted.

"There are many who may not yet understand the importance of [the] third dose of vaccine," said Creech. "By giving an additional dose, particularly of an mRNA vaccine several months after those initial doses, we leverage the immune system's ability to create long-term memory. That 1-2 punch is the best way to protect quickly and protect for a longer period of time."

For other fully vaccinated Americans, a booster may seem unnecessary, for the time being, Dowdy said.

"For those who want protection against serious disease, but don't care if they get a mild infection, the first series is probably sufficient. For those who want to avoid any infection at all costs, they've come to realize that a booster shot - while helpful - is not a 'get out of jail free' card," Dowdy explained.

Despite the fact that omicron has been shown to cause less severe disease, Walensky stressed this week that as a nation, we are still facing a high overall burden of disease.

"Importantly, 'milder' does not mean 'mild.' And we cannot look past the strain on our health systems and substantial number of deaths -- nearing 2,200 a day -- as a result of the extremely transmissible omicron variant," Walensky said.

Hospital officials have repeatedly stressed that the sheer number of infections caused by the new variant could still overwhelm the health care system. Nationwide, there are just under 150,000 COVID-19-positive Americans receiving care -- a total which has just begun to fall after hitting a record high of 160,000 patients earlier this month.

When asked whether the C.D.C. might consider changing the definition of "fully vaccinated" to encourage more Americans to get the additional shot, Walensky reiterated that at this time, the agency is working to ensure people are "up to date" with their vaccinations.

"Right now, we're pivoting our language, we really want to make sure people are up to date. That means if you recently got your second dose, you're not eligible for a booster, you're up to date. If you are eligible for a booster and you haven't gotten it, you're not up to date," Walensky said.

Vaccination campaign must target both the unvaccinated and the unboosted

Experts stress the vaccination campaign must not only focus on the unboosted, but also on the 63 million eligible Americans who remain completely unvaccinated.The efforts should not be perceived as an "either/or situation, but rather a "both/and," said Creech.

"While we want to respect the personal choices that individuals wish to make, we certainly need to invest resources to address misunderstandings or misconceptions that have led them to the decision not to vaccinate," Creech said.

Strategies to increase overall vaccine confidence, as well as to raise awareness about the value of boosters, will also be applicable to vaccines as a whole, Creech said.

"It's not about whether we should be prioritizing boosters over the primary vaccine series, it's about how we message these in a way that prioritizes both," Dowdy added.

Although the omicron surge seems to be sharply declining in many areas of the country, Americans must realize the pandemic is not over yet, Fauci stressed.

"It's vital that we all remain vigilant in the face of this virus," Fauci said. "It's been a long two years. However, please now do your part to lean into this current moment. Now is the time to do what we know works: Wear a mask, get vaccinated and get boosted."