RELATED: If You’ve Done This, You May Not Benefit From a Booster, Experts Say. Jeanne Marrazzo, MD, the director of the division of infectious disease at the University of Alabama at Birmingham, recently told The Washington Post that boosters are especially important for those at higher risk of severe COVID—older adults and people with underlying medical conditions—as colder weather and the holiday season approaches. “Winter is coming,” she said. “We really want everybody to think about it like topping off your antibody levels, like topping off the tank before winter comes.” The official start date of winter for the U.S. is Dec. 21, but depending on where you live, the colder season might start earlier or later. Colder weather adds an additional layer of COVID risk because people are more likely to gather indoors, where the virus can spread more easily from person to person. At the same time, the end of the year in particular typically brings forth more large family gatherings for the holidays. And then there’s the threat of other potential illnesses that could inhibit your immune system, like the flu or the common cold. “The risk [of COVID] is much greater when in a crowd, or in densely packed indoors spaces where someone may carry the virus,” William Li, MD, a physician, virus expert, and medical director of the Angiogenesis Foundation, previously told Best Life. That’s why the CDC says that “even those who are fully vaccinated should wear a mask in public indoor settings in communities with substantial to high transmission.” Jeremy Levin, MD, former chairman of the Biotechnology Innovation Organization and founder of Ovid Therapeutics, also previously told Best Life that people should get their booster shot as soon as possible. “Waiting increases the probability that the immunity gained by the original vaccination will diminish,” he warned.ae0fcc31ae342fd3a1346ebb1f342fcb RELATED: For more up-to-date information, sign up for our daily newsletter. Thankfully, the three vaccines are still substantially protective against serious cases of COVID even without a booster, despite a drop in protection against infection. “The evidence shows that all three COVID-19 vaccines authorized in the United States are safe—as demonstrated by the over 400 million vaccine doses already given. And, they are all highly effective in reducing the risk of severe disease, hospitalization, and death, even in the midst of the widely circulating Delta variant,” CDC Director Rochelle Walensky, MD, said in a statement released Oct. 21, per The Washington Post. Experts maintain that it is still unvaccinated people who are most at risk right now. “For all age groups, the COVID-19-associated hospitalization rate is markedly higher in those who are unvaccinated,” Walensky said during an Oct. 21 White House COVID press briefing. “Too many eligible Americans—about 65 million of them—remain unvaccinated, leaving themselves and their children, families, loved ones, and communities vulnerable.” Large pockets of unvaccinated people do allow the virus to continue to spread and, potentially, evolve. “Worst-case scenario is that another variant emerges,” Jennifer Kates, PhD, the director of global health policy at the Kaiser Family Foundation, told Vox. “COVID has fooled us before and can again. And if people let their guard down … we could see another surge, especially since we are entering winter.” As we’ve seen with the Delta variant, new iterations of COVID have the potential to affect the protection afforded by the initial vaccine series, which is why getting your booster shot before the winter comes could be that much more important. “If another variant comes that has the potential to be highly contagious and evade our vaccines and has some additional mutations, then it makes a lot of sense that this boosting is the right strategy,” Manish Garg, MD, an emergency medicine physician and co-founder of World Academic Council or Emergency Medicine, told Yahoo! Finance. RELATED: Dr. Fauci Says You Need a Booster ASAP If You Got This Vaccine.