The U.S. is pushing to have 70% of adults get at least one dose of the COVID-19 vaccine, but an expert said that number is important to reach at the state level too — and those states who are falling well below may be vulnerable to another outbreak."There are 12 states that are already at 70%. I worry about the ones that are way below that, and they are sitting ducks for the next outbreak of COVID-19 — which shouldn't have to happen now," National Institutes of Health Director Dr. Francis Collins told CNN.Sixty-three percent of adults have received at least one COVID-19 vaccine dose, according to data published Thursday by the U.S. Centers for Disease Control and Prevention. But President Joe Biden has set a goal of having that number at 70% by July 4.That goal has met a significant obstacle — a dwindling number of people who want to get vaccinated.The seven-day average of newly administered doses has fallen below 1 million per day for the first time since January, according to data from the CDC.The director of the CDC said that there is no magic target for herd immunity, but that she thinks getting to 70% would go a long way toward protecting the community."We have pockets of this country that have lower rates of vaccination," Dr. Rochelle Walensky said. "I worry that this virus is an opportunist and that where we have low rates of vaccination are where we may see it again. And so really the issue now is to make sure we get to those communities as well."Alaska, Arkansas, Georgia, Idaho, Louisiana, Mississippi, Oklahoma, Tennessee and Wyoming are among the states with the lowest vaccination rates.And for those who feel they don't need the protection of the vaccine, Collins said to think of getting doses as a "donation" to those in communities who — for reasons like chemotherapy and organ transplants — aren't necessarily protected against COVID-19 by vaccinations.Cash prizes and nightlife vaccinations to get through the 'slog-phase'The big challenge for officials is reaching people who are not eager to get the vaccine."We're making a lot of progress, but frankly, we're entering kind of the slog-phase of the vaccination campaign, where the people who are most eager to have it and most able to get it, have gotten it," former CDC director Dr. Tom Frieden told CNN."Now we need to continue to make it easier to get and to address people's concerns," he said, adding that the vaccine is "astonishingly effective and very, very safe."In an effort to increase convenience for younger residents, New York City officials will park mobile vaccine buses outside popular nightlife destinations, Mayor Bill de Blasio said Thursday.In addition to access and education improvement, more companies and officials are offering incentives to sign up for inoculation.Kroger Health announced Thursday that it is launching a $5 million #CommunityImmunity giveaway to motivate more people to get the vaccine.Between June 3 and July 10, Kroger Health will give $1 million to a winner each week for five weeks as well as 50 "groceries for a year" prizes, a release from the company said.Washington Gov. Jay Inslee announced the "Shots of a Lifetime" giveaway series to incentivize vaccinations in the state.Awards will include cash prizes totaling $2 million, tuition and expense assistance for higher education, sports tickets and gear, gift cards, airline tickets as well as game systems and smart speakers, he said."We're making this investment today because we know every life in the state of Washington has value," said Inslee. "I'm excited to announce these strong incentives that will bring the potential to save thousands of lives." Will young students return to school with masks?Meanwhile, Walensky expressed a particular concern about vaccinating young people, citing a rise in the number of young people hospitalized this spring which should "force us to redouble our efforts.""I want to highlight a specific population that we were hoping will join the tens of millions who have already been vaccinated — and that is adolescents," Walensky said on Thursday. In May, the U.S. Food and Drug Administration expanded its authorization of the Pfizer COVID-19 vaccine to include the younger ages of 12 to 15.Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, said on CNN's New Day on Thursday that he is "cautiously optimistic" that children younger than 12 could get a COVID-19 vaccine by Thanksgiving."We are now doing studies that are ongoing as we're speaking, studies that are looking at what we call age de-escalation, children from 12 to 9 and then 9 to 6 and then 6 to 2 and then 6 months to 2 years," Fauci told CNN.While Thanksgiving may be a quick timeline in the development of vaccines, it poses a particular problem for students who may be in school months before they can be vaccinated.That could mean children younger than 12 returning to school in the fall wearing masks, though Walensky said the policy is being revisited.When asked if there might be a change to mask guidance in time for school in the fall, Walensky said, "I think we will. We are looking at the evidence now and we will be coming out with that guidance, soon to come."