Updated: December 1, 2021 4:38 PM EST | Originally published: November 23, 2021 11:54 AM EST

On Nov. 19, Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention (CDC), supported an advisory committee’s advice and expanded the group of people who can now get COVID-19 booster doses to include all adults over age 18.

On Nov. 29, as reports of the Omicron variant started to mount around the world, the CDC strengthened that recommendation from giving people to option to get boosted to say that all adults “should” get a booster shot.

The advice comes as the first case of Omicron was reported in the U.S., in a woman in California who recently traveled from South Africa, where the first cases of the new variant were reported. The woman is isolating and recovering at home, and her close contacts have tested negative.

The CDC’s revised booster recommendation is an effort to bolster people’s protection against Omicron even as the agency’s scientists and other public health experts scramble to learn exactly how well the vaccines protect against the new variant. Those studies, says Dr. Anthony Fauci, chief medical advisor on COVID-19 to President Biden, will take another two to four weeks. In the meantime, he and other experts are advising people who are unvaccinated to get vaccinated, and for people who are vaccinated to get a booster dose, on the assumption that the vaccines will continue to provide some protection against severe disease with Omicron, even if studies end up showing it’s not as high as the 94% or 95% efficacy that the shots initially showed against the earlier version of the virus.

And for people wondering about whether they should wait to get a booster because they might need an Omicron specific dose soon, health experts say don’t wait. Although vaccine makers are developing a vaccine directed against the Omicron variant, and predict it will be ready for testing in about six weeks, the vaccine would still need to be tested for safety and efficacy and that will take another few months. So at the earliest, an Omicron vaccine won’t be available until spring.

That increases the urgency for booster shots, a bit of an about-face from the situation before Omicron emerged. Before the new variant, many people didn’t feel the same urgency to get a booster as they did to get vaccinated in the first place, with some people not quite clear about how necessary the booster is. Studies show that the original doses of all three vaccines currently approved or authorized—two doses of the Pfizer-BioNTech or Moderna shots, or one dose of the J&J-Janssen shot—continue to protect people from getting severe disease and needing to be hospitalized. Studies looking at the vaccines’ effectiveness against Omicron are ongoing, but so far reports from South Africa suggest that the cases seem to be mild. Dr. Anthony Fauci, chief medical advisor on COVID-19 to President Biden warned, however, that those reports are early and anecdotal, and that the definitive studies haven’t been completed yet.

The question of how urgently boosters are needed was considered carefully by the CDC’s panel of experts, as well as the Food and Drug Administration’s (FDA) advisory committee in making their recommendations about boosters, even before Omicron. Initially, for example, the FDA committee decided to recommend boosters for adults who live or work in settings that put them at higher risk of getting infected, but the CDC panel opted to limit boosters to those at highest risk for severe disease—people over age 65 and those with underlying health conditions. Walensky, however, broadened the booster-eligible group to include those who also work or live in settings where they might be more likely to get exposed to SARS-CoV-2, such as health care facilities, grocery stores, prisons, homeless shelters and schools. The CDC initially allowed people in this group to choose whether they wanted to get a booster or not, but has since recommended boosters as a way to protect against Omicron until more information on the variant is available.

Prior to Omicon, health experts have been back and forth over how urgent the need for boosters is. In a press briefing on Nov. 22, Walensky said “everyone over 18 years of age is eligible to get boosted. So, if you’re 18 years and older, I encourage you to go get boosted.” But that fell short of recommending that people get boosted, says Dr. Leana Wen, professor of health policy and management at George Washington University. “The issue is whether the booster is essential vs. nice-to-have. Right now the guidance is phrased as the original vaccination provides pretty good protection, and if you want to get a little extra protection, get boosted,” she says. “That is not the case. Seeing [studies] that found protection from the vaccines declines from the high 80% to 90% to 40% after five or six months —that is not nice-to-have. The booster is not like topping up the immune protection; it’s more like game-changing.”

Dr. Anthony Fauci, the Biden Administration’s chief medical advisor on COVID-19, is equally adamant about the necessity of booster doses. He tells TIME that in his recent broadcast interviews, “I came down very strongly that I thought saying ‘should’ vs. ‘may’ has done nothing but confuse people,” he says. “If you really want people to get a booster, just tell them what to do.”

Fauci points to growing data from a number of countries, including the U.S., that support the need for boosters now. That evidence consistently indicates that infections, hospitalizations and deaths are several-fold lower in those a month after receiving a booster dose, compared to those who only received the original vaccine. In fact, early data suggest that a booster dose may lead to an enhanced level of protection in terms of higher levels of virus-fighting antibodies, as well as longer-lasting protection, than the original vaccine doses.

The question of whether boosters are necessary or a luxury comes down to what the goals of vaccination are: if you want to prevent serious disease and reduce hospitalizations, the original vaccination continues to do that pretty well. But if you want to prevent breakthrough infections, boosters are critical. “Right now we are facing more than 90,000 new infections a day [on average], we are entering the winter season, and people are gathering for the holidays,” says Wen. “We know immunity to symptomatic infection wanes substantially at the six-month mark, and immunity even to severe disease wanes too. It’s mind-blowing to me that we cannot just be straightforward with people at this point, and say it is essential to get a booster. The CDC playing around with ‘should’ vs. ‘may’ wording has further confused people.”

So should you get a booster? Essentially, it couldn’t hurt. With the first case of Omicron reported in the U.S., and with 29 states currently recording new highs in daily COVID-19 cases—coupled with the winter season of colds, flu and other respiratory infections—having the added protection of a booster makes sense. That’s especially true if you’re planning on traveling over the holidays, and mixing with people who aren’t from your household in airports or on planes, trains or buses, and then mingling with family from different households as well. If you have small children who either aren’t yet vaccinated or are only partially inoculated, there’s even more reason to build up a cushion of immunity to surround those who are less protected.

Getting a booster is your choice, but it’s one that could affect family and friends around you. “Many people think the booster is a luxury, as opposed to something they need to get,” says Wen. “That messaging needs to change urgently.”

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