Pandemic-weary Americans have employed a particular dependent clause so often that it has become a cliche: "When things are back to normal ..." 

Kids back to school. Parents back at work. Bars. Gyms. Concerts. Travel. Dinner parties.

It is a phrase as optimistic as it is anticipatory. But it hides a burning question: When will things be normal again?

Anthony Fauci, the nation's top infectious-disease official, gets this question several times per week, and he is aware of how closely Americans are following his every prediction amid the coronavirus pandemic.

"No, you know, I can't say that, Dana," Fauci told CNN's Dana Bash when she asked him on Sunday whether his timeline for a return to normality had been pushed back by a year or more. "Because then it will be a sound bite that's not true. I'm saying: We don't know."

If consensus among experts on this subject exists, it is that nobody really knows when normal will return. Fauci also said masks - for many Americans, one of the most visible signs of abnormality - may still be necessary in 2022.

"I think it is possible that is the case," he said when asked whether Americans will still be wearing masks next year. The level of new infections must go "way down," he added, before he could say people will not need face coverings.

"I want it to keep going down to a baseline that's so low there is virtually no threat," Fauci said. "If you combine getting most of the people in the country vaccinated with getting the level of virus in the community very, very low, then I believe you're going to be able to say, you know, for the most part, we don't necessarily have to wear masks."

The closest Fauci got to discussing a specific timeline came when he agreed with President Joe Biden's forecast on Friday that "we'll be approaching normalcy by the end of this year, and God willing this Christmas will be different than last."

"As we get into the fall and winter, by the end of the year, I agree with the president completely that we will be approaching a degree of normality," Fauci said Sunday. "It may or may not be precisely the way it was in November of 2019, but it will be much, much better than what we're doing right now."

In general, there are too many unknowns to say definitively when the coronavirus pandemic will end. This is why Biden followed his hopeful projection with a disclaimer: "But I can't make that commitment to you. There are other strains of the virus. We don't know what could happen in terms of [vaccine] production rates. Things could change."

The Biden administration has struggled with this temporal fuzziness early on, especially when it comes to children returning to school - which the president stated was a priority for his first 100 days in office.

"It really depends on what you mean by 'normality,'" Fauci said in the CNN interview. "If normality means exactly the way things were before we had this happen to us, I can't predict that."

The end of the year is longer than many people had believed they'd need to wait for "approaching a degree of normality" - months later than the end of July, when Biden says the country will have enough vaccines for nearly all Americans.

But vaccines alone have not been an immediate panacea, as experts have warned. There are four reasons.

First, production and distribution can be unpredictable and susceptible to delay. The winter storms that have devastated much of the United States, and especially Texas, held up the injection of millions of vaccine doses. In the past week, 1.37 million people were vaccinated each day, a 15% decrease from the week before, according to Washington Post tracking.

Second, polling has shown that even with widespread vaccine availability, people may still be hesitant to receive one. In a Washington Post-ABC News poll last month, 33% of respondents said they "probably" or "definitely" will not get a coronavirus vaccine.

Third, younger children probably will not be vaccinated until "the beginning of the first quarter of 2022," Fauci said in another TV interview Sunday. For some, normal will not come until everyone in the family - children included - is protected.

"I have a 7-year-old and they're not even testing that age group yet," Tara Smith, an epidemiologist at Kent State University, said on Twitter last month. "At least for us, we can't have a 'new normal' without knowing he's also protected."

Fourth, research is still ongoing about how big an impact the coronavirus vaccines will have on asymptomatic transmission. The vaccines are effective at protecting people from developing COVID-19 symptoms, but experts suggest that people continue following precautions such as mask-wearing and social distancing until they have more data about the virus's silent spread.

Angela Rasmussen, a virologist at Georgetown University's Center for Global Health Science and Security, wrote a long Twitter thread in January about climbing out of the "very deep well" that the pandemic has plunged the country into. Both vaccines and measures such as mask-wearing are key to scaling the ladder up, out of the well and into the light, she wrote.

"We must be cautious, especially when not many people have been vaccinated," Rasmussen said. "It doesn't mean we'll be wearing masks and distancing indefinitely or that we release the ladder in despair. It means we grip the ladder tighter, fix our gaze on the light, and keep climbing."