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As COVID-19 hospitalizations rise and the holiday season draws nearer, a familiar question lingers: when is the best time to get the latest shot?

Earlier this month, the FDA approved and the CDC recommended the updated mRNA COVID-19 vaccines that solely target the XBB.1.5 Omicron subvariant for people ages 6 months and up to prevent serious illness.

But some experts told 番茄社区 that although it is a good idea to get vaccinated as soon as you can, there's more nuance to the question.

Ann M. Sheehy, PhD, an immunologist from the College of the Holy Cross in Worcester, Massachusetts, said she wouldn't even refer to these new COVID shots as "boosters."

"It's a new vaccine, and I think people are making a concerted effort to call it the '2023-24 COVID vaccine,' because 'booster' kind of implies it's the same as what it was before," she noted. Like flu vaccines, updated COVID vaccines will match currently circulating strains every year.

David O. Freedman, MD, FIDSA, an infectious disease specialist speaking on behalf of the Infectious Diseases Society of America, pointed out that of the respiratory syncytial virus (RSV), influenza, and COVID-19 shots, "the highest priority definitely is the COVID vaccine, and people should really get that first and as soon as possible, because the strains have changed."

One exception is people who were recently infected with COVID-19, who should wait around 3 months until their natural immunity wears off to maximize their protection, he added. Of the bivalent vaccines, which came out over a year ago, he said that they just don't work anymore, and they only seemed to be effective for about 4 to 6 months.

Experts also said that waiting until right before the holidays wouldn't offer much of a benefit. According to Sheehy, new antibodies from the shot take around 3 weeks to form. "You want to include that in your calculator [of] when you want to get this ... We're coming up on October 1. If you get it at day zero, your best protection is probably somewhere in mid to late October, and then you're typically covered for at least 4 months from there."

Sheehy said that she personally plans on getting the shot at the end of next week. "It means I'll be covered for any Thanksgiving travel, anything that I do at Christmas or New Year's. And then I hope that it stretches all the way to around that March 1 deadline, when I'm probably going to be out biking and running again."

Paul Offit, MD, of the Children's Hospital of Philadelphia, emphasized that the shot does not become ineffective after 4 months, but rather has the best protection against mild illness for that duration.

However, he has a slightly different perspective on the new shots. People who are at the highest risk for serious illness should be the only ones rushing to get the new COVID vaccine, he said.

"Anybody who wants it can reasonably get it, but I think we should really focus on those who are most likely to benefit," Offit said, which includes older adults, pregnant people, and the immunocompromised, along with those who live with them, "because that's the goal of this vaccine, to prevent severe disease."

After that, timing isn't so important, he noted. "I'm not sure it makes much difference. The assumption is that this is a winter virus, even though the seasonal pattern isn't quite clear yet."

Another factor in timing is delayed vaccine availability, according to a number of recent , with customers who scheduled appointments for the shot being turned away by pharmacies, or being billed for the cost of the shot that by insurers, likely due to a shift in standard commercial ordering and payment structure for the vaccines.

While the government previously distributed free vaccines directly to vaccination sites, now "doses go to large warehouses owned by either pharmacy chains or drug wholesalers," Freedman said. "These middlemen now don't get paid for a dose until it goes into someone's arm and insurance kicks in."

Insurers must also update their systems to cover the new vaccines.

Unlike before, Freedman noted, pharmacy chains and wholesalers must deal with quantities that reflect demand, so supply doesn't sit for too long and go to waste. "If spot shortages persist, then guidance needs to be given to prioritize the vulnerable on any given day at a given injection point," he added.

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