Washington -- Coronavirus infections could be driven to low levels and the pandemic at least temporarily throttled in the United States by July if the vast majority of people get vaccinated and continue with precautions against viral transmission, according to a report released Wednesday by the Centers for Disease Control and Prevention.

The report comes as administration officials and leaders in many states are sounding more confident that the country can return to a degree of normalcy relatively soon. President Joe Biden on Tuesday announced a new vaccination goal, saying he wants 70% of adults to have had at least one dose by July 4.

CDC Director Rochelle Walensky said Wednesday that the modeling results give Americans a road map out of the pandemic - so long as they continue to get vaccinated and maintain mitigation strategies until a "critical mass of people" get the shots.

"The results remind us that we have the path out of this, and models, once projecting really grim news, now offer reasons to be quite hopeful for what the summer may bring," she said.

The CDC report is not a prediction or forecast. It is a set of four scenarios based on modeling of the pandemic, using different assumptions about vaccination rates, vaccine efficacy and precautions against transmission.

Each scenario shows an epidemic curve in which the national increase in cases that began in early March hits a peak and plummets in late spring, leading to a significantly improved viral landscape this summer. In the less optimistic scenarios, hospitalization numbers will vary significantly from state to state.

Under the most optimistic scenario, deaths linked to covid-19, the disease caused by the novel coronavirus, could drop into the low 100s per week in August and into the "tens" per week in September, according to Justin Lessler, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health and one of the paper's senior authors. More than 4,000 people a week are dying of the disease, and about 578,000 people in the United States have died of covid-19 since the start of the pandemic.

That model includes an assumption that 90% of those eligible for vaccine would get a shot, which Lessler acknowledged "may be on the optimistic side given rates of vaccine refusal in some areas."

Infectious-disease experts caution that the number of new infections remains high. Variants of the virus could emerge with mutations that allow the pathogen to evade vaccines. Immunization hesitancy among large chunks of the population is another concern. High rates of vaccination seen in early April have come down in the past several weeks.

And the long-term picture remains cloudy because of all the unknowns about this virus, which continues to circulate freely around the planet and is driving catastrophic outbreaks in Brazil, Colombia, India and other countries. Some epidemiologists say that even if the coronavirus is suppressed to low levels this summer in the United States, it will rebound in the fall.

There are limitations to the modeling. Although the researchers factored in the highly transmissible coronavirus variant B.1.1.7 now dominant in the United States, it did not contemplate what would happen if an even more problematic variant - for example, one that could evade vaccine-induced immunity - were to spread.

The models used data through March 27. The report did not capture the high rate of vaccinations in April, when more than 90 million doses went into arms, according to Washington Post vaccine tracking data. Instead, the report considered 60 million to be a high vaccination rate in April. The high rate of vaccinations so far has made the most optimistic scenario more likely, Lessler noted.

Attempts to model the trajectory of the pandemic have had a rocky history going back to the spring of 2020. Some models predicted steep declines in infections that did not materialize. The virus has repeatedly surprised infectious-disease experts and has shown a pattern of resurgence when people let down their guards.

Officials said people and communities need to maintain some efforts, such as wearing masks, to limit viral transmission. But the new report suggests that vaccination is the key to improvement.

"Vaccines matter most. That's the one that's really going to drive the numbers down the most," said Katriona Shea, a professor of biology at Penn State and one of the senior authors of the report.

"It's absolutely possible to get a full rebound," she said. "But if we can get enough vaccine uptake and high enough compliance with [precautions], it is possible to bring it down."

How low the numbers get depends on vaccinations and "non-pharmaceutical interventions," which include wearing masks and social distancing. The report makes clear the American public will play the key role in determining the speed with which the threat of contagion is eased and whether the coronavirus will have the opportunity to surge anew.

Infection numbers have been dropping nationally since mid-April, and hospitalizations and deaths are also coming down, although more slowly. With more than half of U.S. adults having received at least one dose of vaccine, and with millions more having recovered from an infection, immunity to the coronavirus is increasingly widespread and impeding spread of the virus.

Working against that: the relaxation of public precautions and the rapid increase in social interactions as people emerge from relative isolation and resume, to some degree, their pre-pandemic lives. This is happening even as the virus is causing close to 50,000 new infections a day.

The new models show "a potentially bumpy path between now and the early to midsummer," Lessler said. But he added that all six of the modeling teams that contributed to the CDC report envision a summer in which case numbers are low and outbreaks under control.

William Hanage, an epidemiologist at Harvard University's T.H. Chan School of Public Health, said the report shows that increases in illness are possible in coming months and could produce "hospitalizations worth taking seriously," even if deaths are limited by high vaccination rates among the elderly.

"In some ways this is just more of what we knew: more vaccines good, less vaccines bad," he said. Adding other measures to stanch viral spread remains critical, he said.

The pandemic will not be over even if the numbers drop to low levels this summer. A significant number of people have said they will not receive the vaccine. The number of "susceptibles" will remain in the tens of millions. The coronavirus will still find ways to circulate.

Walensky said Tuesday during a "fireside chat" webinar that she expects the current infection numbers to continue their decline. She also warned against complacency, noting that there are many unknowns, including the mutated virus variants circulating across the globe.

"If we're not humble at this point, we have a problem," she said.