(CNN) It's easy to get caught up in all the good news about the Covid-19 pandemic.
Vaccine advisers to the US Centers for Disease Control and Prevention unanimously voted Sunday to recommend the distribution of a third vaccine for Americans 18 and older: the one-dose Johnson & Johnson vaccine.
And for the first time since early November, fewer than 50,000 patients are hospitalized with Covid-19.
Along with that, there's been a decrease in new cases and deaths since the abysmal January surge.
Despite that progress, Dr. Anthony Fauci warns some Americans are easing up on safety measures too soon -- threatening the same post-dip surges we suffered in 2020.
"Just look historically at the ... early spring of 2020 or the summer of 2020, when we started to pull back prematurely. We saw the rebound," said Fauci, director of the National Institute of Allergy and Infectious Diseases.
That false sense of security and rebound led to another wave of shutdowns last year.
But this year, Americans face a new challenge: the increased spread of troubling variant strains -- including some that appear to be homegrown.
That's why health experts say Americans who want to get life back to normal must keep physical distancing -- and get vaccinated as soon as they're able to.
With the new Johnson & Johnson approval, CDC Director Dr. Rochelle Walensky officially signed off on the recommendation Sunday.
Distribution of the Johnson & Johnson vaccine will begin Sunday night, according to senior administration officials who also cautioned that the amount of vaccine made available will be uneven throughout the month of March.
"Starting tonight, 3.9 million doses of J&J will be distributed across all channels, states, tribes, territories and pharmacies and community health centers," an official said in a briefing call Sunday night. "Those J&J doses will be delivered as early as this Tuesday morning."
The official also said that Johnson & Johnson communicated with the White House "that the weekly supply will be limited for the next couple of weeks after the initial distribution."
"The initial distribution is nearly four million doses of J&J. That's the entirety of J&J's current inventory," The official said. "We do not expect any additional deliveries next week and we expect deliveries to be uneven during the weeks of March."
The vaccine was given emergency use authorization by the US Food and Drug Administration on Saturday. An FDA analysis found the vaccine safe and effective.
It's the third coronavirus vaccine to win emergency use authorization, after Pfizer/BioNTech's and Moderna's vaccines.
A White House official said all three vaccines will be distributed evenly across all channels, but stressed that that does not mean that every vaccination site will have every vaccine.
The Johnson & Johnson vaccine can be kept at normal refrigerator temperatures for three months and -- unlike the two other vaccines -- requires only one dose, something that committee members said would make it easy to distribute and administer.
The CDC's Advisory Committee on Immunization Practices did not make any specific recommendations for which groups should have priority for the vaccine, made by Johnson & Johnson's Janssen vaccine arm.
The vaccine could help "save costs and lives" and benefit health equity, Dr. Sara Oliver, an officer with the CDC Intelligence Service, told the Advisory Committee on Immunization Practices on Sunday.
"During a pandemic, the data show that the best utilization of resources is to employ all available vaccines with acceptable vaccine efficacy. This will save cost and lives," Oliver said.
She added the vaccine would help with health equity. A single-dose vaccine has an advantage, particularly in settings where a second dose would be challenging.
For example, it could be used to help protect the homeless, people in the justice system, and those with limited access to health care, such as people who are homebound or live in rural areas, Oliver said.
"To have a third vaccine that meets the expectations of an (emergency use authorization) for safety and effectiveness at preventing severe disease and death from COVID-19 brings us one step closer to protecting the American public, staying ahead of concerning viral variants, and finding our way out of the pandemic," National Institutes of Health Director Dr. Francis Collins said.
The fact that the Johnson & Johnson vaccine requires only a single dose makes it a game-changer, said Dr. Esther Choo, a professor of emergency medicine at Oregon Health & Science University.
"It's been such a challenge to get even a single dose to many people," she said. "Signing up for a second one, keeping track of that, getting transportation, it's just a huge barrier for many Americans and then of course in harder-to-reach places, including rural America, it's just been a huge logistical challenge."
Now that the Johnson & Johnson vaccine has proven to be safe and effective in adults, the company will begin studies with children, said Dr. Macaya Douoguih, head of clinical development and medical affairs with J&J's vaccine arm, Janssen.
"We will conduct several immunogenicity and safety studies in children from 17 years of age down to neonates," Douoguih told a CDC advisory committee Sunday.
"The study in adolescents, we hope, will open next week. We are also anticipating a study in pregnant women in the second and third trimesters toward the end of March, early April," Douoguih said.
Johnson & Johnson also plans to begin study in immunocompromised individuals in the third quarter of this year, Douoguih said.
The FDA's emergency use authorization for the Johnson & Johnson vaccine is currently for use in adults 18 and older.
The Pfizer/BioNTech vaccine has been authorized for people 16 and older, and the Moderna Covid-19 vaccine has been authorized for people 18 and older.
Both Moderna and Pfizer have started enrolling children in Covid-19 vaccine trials.
The Johnson & Johnson vaccine will also help boost the number of shots available to Americans as health officials race to prevent another possible Covid-19 surge fueled by variant strains.
So far, more than 48.4 million Americans have received at least their first dose of a Covid-19 vaccine, CDC data shows.
More than 23.6 million people have gotten both doses of a vaccine. That's about 7.1% of the US population.
"The J&J vaccine, which is easier to transport and store ... is going to dramatically increase our vaccine availability," said Dr. Jonathan Reiner, a professor of medicine at George Washington University.
About 3.9 million doses will be available for ordering right away, said Lori Tremmel Freeman, CEO of the National Association of County and City Health Officials. That could add about 25% more Covid-19 vaccination capacity for states.
Utah Gov. Spencer Cox told CNN he expects the state will receive "several thousand doses" over the next few days.
"We expect shots in arms this coming week," Cox said. "We know they have about 4 million doses on hand right now ready to go out. They'll start shipping those out, we believe, on Monday. We should have those shots, we think, on Wednesday. And shots in arms on Thursday and Friday. That's a big deal for our state and for Americans everywhere."
While news of another Covid-19 vaccine is worth celebrating, the US is still a long way off from herd immunity. That's when enough people are protected against a virus that it cannot spread through the population.
More than 48,800 people are still battling Covid-19 in hospitals, according to the COVID Tracking Project. That's down from a record-high 132,447 patients on January 6.
But more than 63,800 Americans have died from Covid-19 just this month, according to Johns Hopkins.
"This third safe, effective COVID-19 vaccine comes at a potentially pivotal time," Walensky said in a statement Sunday.
"CDC's latest data suggest that recent declines in COVID-19 cases may be stalling and potentially leveling off at still very high numbers. That is why it is so critical that we remain vigilant and consistently take all of the mitigation steps we know work to stop the spread of COVID-19 while we work our way toward mass vaccination," she said.