President Joe Biden received the second dose of the Pfizer-BioNTech vaccine near his home in Delaware on Jan. 11—so it's clear the president has surpassed the two-week waiting period to build up immunity to the novel coronavirus. Despite that, Biden is still wearing masks indoors—and some have questioned why. On May 9, Jeffrey Zients, the White House's COVID-19 Response Coordinator, addressed the president's reasoning during on CNN's State of the Union. Keep reading to find out what he had to say about Biden's decision to continue wearing masks indoors. Zients says Biden is still wearing a mask inside because it aligns with CDC guidance State of the Union host Jake Tapper showed a recent video of the president saying: "When I'm inside it's still good policy to wear the mask." He then proceeded to ask Zients if it's "really necessary for a fully vaccinated person to wear a mask at a limited indoor gathering, if everyone there is vaccinated."Zients responded by recounting a recent CDC guideline change, which suggests people who are fully vaccinated can attend a small indoor gathering with friends and family without a mask. Tapper quickly followed up with the question: "So why does President Biden in a room full of journalists, if you've got everybody in that room vaccinated, why does he need to wear a mask?"The answer, according to the government official, is that Biden is "going to continue to follow the CDC guidance." He added: "It's just a matter of a few weeks ago when all states made vaccines eligible for all Americans." Zients then suggested there are many people who are still waiting to get their second shot and others who haven't been vaccinated at all.RELATED: The CDC Says to "Avoid" Going Here, Even If You're Vaccinated. The CDC updated its guidelines last month to say fully vaccinated people can gather indoors without masks. On Apr. 27, the CDC updated its guidelines on masking. And although fully vaccinated and unvaccinated people must still wear a mask in most situations as a preventative measure, people who have received the COVID jab can spend time with other vaccinated people indoors without a mask or keeping a distance of six feet. Vaccinated people can also gather indoors with one other unvaccinated household "without masks or staying 6 feet apart." The only exception to that is if someone in that household is at an "increased risk for severe illness from COVID-19."However, the CDC notes: "In indoor public spaces, the vaccination status of other people or whether they are at increased risk for severe COVID-19 is likely unknown. Therefore, fully vaccinated people should continue to wear a mask that fits snugly against the sides of your face and doesn't have gaps, cover coughs and sneezes, wash hands often, and follow any applicable workplace or school guidance."And for more COVID news delivered right to your inbox, sign up for our daily newsletter. Biden has been criticized for "missing the biggest opportunity to reduce vaccine hesitancy" by continuing to wear a mask indoors. Leana Wen, MD, a public health professor at The George Washington University and Baltimore's former health commissioner, discussed Biden's decision to wear a mask indoors in a Washington Post op-ed, published on Apr. 29. "Of course, you wouldn't know that the vaccines are so effective by looking at the CDC's overly-cautious guidelines. Already, a very damaging narrative is taking hold: If the vaccines are so effective, then why so many precautions for the fully vaccinated? What's the point of getting inoculated if not much changes?" she wrote.Wen said in wearing a mask at his Apr. 28 Congressional address, Biden "missed his biggest opportunity to reduce vaccine hesitancy." Wen said the major issue was the setting of the event, which had 200 attendees in the House chamber, which can hold 1,600 people, and everyone was vaccinated.Currently, more than 40 percent of the adult U.S. population is fully vaccinated, according to the CDC. But experts warn the remainder of the population hasn't been vaccinated not because they can't get appointments, but because they're worried or outright don't want to get the shot. Experts like a former FDA chief recently suggested the CDC start lifting indoor mask restrictions. Former FDA commissioner and physician Scott Gottlieb, MD, suggested the CDC lift indoor mask restrictions on CNBC's The News with Shepard Smith on May 6. "I think we should start lifting these restrictions as aggressively as we put them in. We need to preserve the credibility of public health officials to perhaps reimplement some of these provisions as we get into next winter, if we do start seeing outbreaks again," Gottlieb said. "Even if vaccination rates are slowing, we're still going to continue to chip away at getting more people vaccinated…but I think that these gains are locked in."Referring to Gottlieb's recommendation, Zients told Tapper: "We're going to look towards the CDC. The president from day one said we're going to rely on science and facts, and that's what we'll do." Gottlieb, however, reiterated his suggestion on CBS News' Face the Nation on Sunday morning. "We're at a point in time where we can start to lift these [COVID-19] ordinances," he explained. "People have to judge their own individual risk based on their own circumstances."RELATED: The CDC Says Don't Do This Until 4 Weeks After Getting Vaccinated.