By Madeline Holcombe, CNN

(CNN) -- With fears growing the US may be facing a fourth surge of Covid-19 cases, health experts are pleading with Americans to keep taking precautions until they are fully vaccinated.

"Please wait until you're fully vaccinated before you're traveling, before you're engaging in high-risk activities," said CNN Medical Analyst Dr. Leana Wen. "No doubt when you become vaccinated, the activities that were once higher risk are now going to be lower risk and so just wait until then."

Wen said she worries the US is on the "precipice" of a fourth surge as data is showing that infections are now skewed toward a younger generation.

Her sentiments were echoed by Dr. Anthony Fauci, who told NBC Nightly News that while he is feeling some Covid-19 fatigue himself, it is important the US continue taking precautions while vaccinating Americans.

"We need to hold out just a bit longer and give vaccines a chance to really get the upper hand in this," Fauci said. "I'll guarantee as we get into the late spring and the early summer, you're going to see a return to gradual degree of normality that everyone is hoping for, but we don't want to do it prematurely."

High on the list of factors worrying experts is the spread of coronavirus variants in the US.

Michigan on Thursday said it identified its first case of a variant that was originally found in Brazil, adding to reports of variants spreading across the US. That spread, along with relaxation of social distancing and mask mandates in many states, contributed to an influential model increasing its prediction of the number of people who will die of the virus by July 1.

Last week, the University of Washington's Institute for Health Metrics and Evaluation (IHME) forecast that 600,000 people would die by the start of July, and this week that number is up to 609,000.

"Relatively small changes in behavior can have a profound impact on deaths in the near term," the IHME said.

More than 30.5 million people in the US have been infected with coronavirus and 553,120 people have died, according to data from Johns Hopkins University.

CDC: Travel is low risk if vaccinated

You have yet another reason to get vaccinated.

In new guidance Friday, the US Centers for Disease Control and Prevention said people who are fully vaccinated against Covid-19 can travel at low risk to themselves.

So long as coronavirus precautions are taken -- including wearing masks -- fully vaccinated people can travel within the United States without first getting tested or quarantining afterward.

Fully vaccinated people traveling internationally do not need a Covid-19 test beforehand unless required by the destination, the CDC said. And they do not need to self-quarantine upon return to the US.

Travelers should have a negative Covid-19 test before boarding a flight back to the US, the CDC noted, and a follow-up test three to five days after their return.

According to the CDC, an individual is considered fully vaccinated two weeks after receiving the last required dose of a Covid-19 vaccine -- whether that be the second dose of vaccines by Pfizer/BioNTech and Moderna, or the single dose required by Johnson & Johnson.

Anyone not fully vaccinated should continue to avoid travel, the CDC advised. If they must travel, they should get tested one to three days before and again three to five days after. They should also self-quarantine at home for seven days, or 10 if they did not get tested post-travel.

Additionally, all Americans should wear a mask and practice public health measures when traveling, regardless of their vaccination status.

Vaccinations now can prevent future Covid-19 variants, surgeon general says

According to US Surgeon General Dr. Vivek Murthy, while Covid-19 vaccines appear to provide protection against the identified variants of the coronavirus, vaccination is also important to prevent viral mutation in the future.

"The good news is that the vaccines that we have to date have proven to be both safe and effective, including against the variants," Murthy told MSNBC on Friday. "Our concern is that in the future, some of those variants may be much more resistant to protection from a vaccine."

He described the current situation in the US as a race between vaccines and variants. The potential development of coronavirus variants is a motivating factor to further increase vaccination rates, Murthy said.

"The more quickly we get people vaccinated, the more we'll be able to lower the overall amount of infection in our community," he said.

"When that infection is high, there are more chances for the virus to replicate, to mutate and lead to these variants."

What Easter will look like for those who are vaccinated

For fully vaccinated Americans, the Easter holiday can more resemble that sense of normal.

People who have been fully vaccinated are safe to celebrate Sunday indoors with other fully vaccinated people without wearing masks, according to the CDC.

For those who aren't fully vaccinated, the CDC advised they stick to their own household for egg hunts or enjoy these traditions outdoors while 6 feet apart, according to a series of tweets.

The CDC says it's still learning how vaccines protect against the coronavirus and advises that fully vaccinated people going out in public still wear masks and take precautions until the agency knows more.

Officials and experts are hoping to get Americans vaccinated quickly.

Nearly 154 million doses of Covid-19 vaccine have been administered across the country, according to data from the CDC. Thirty percent of the US population -- about 99.6 million people -- has received at least one dose of vaccine, and nearly 17% -- about 56 million people -- have been fully vaccinated.

Pfizer vaccine protects for at least 6 months, but could last years

The protection offered by the Pfizer/BioNTech's coronavirus vaccine remains high for at least six months, the companies said Thursday -- but that's "the floor, definitely not the ceiling," according to Wen.

"Most likely the protection that the vaccine will provide will be years even," she said. "But we just don't know that."

Wen added there was a possibility people may need a booster shot. "But I think that's a small price to pay now that we have these safe and very effective vaccines that are out there."

The protection from those vaccines will soon be available to many more people as states expand their eligibility.

Thursday was the first day all Connecticut residents 16-years-old and older were eligible to be vaccinated, Gov. Ned Lamont said during a press conference.

Residents made more than 100,000 vaccine appointments, Lamont said, and the state will likely have the supply to outstrip demand by late April.

All Maryland residents 16 and older were able to pre-register for an appointment at a mass vaccination site Thursday, Gov. Larry Hogan said.

"The first federal mobile vaccination units in the nation, arrived at the Maryland Emergency Management Agency headquarters in Reisterstown," the governor said Thursday. "In the coming days, these 32-foot trailers will be fanning out across the state."

Maine moved up the date that all adults are eligible from April 19 to April 7, Gov. Janet Mills announced Thursday.

"While this is a great step forward, Maine people should keep in mind that it will still take time to get an appointment and get a vaccine. We will continue to work with vaccine providers across Maine to get shots into arms as quickly as we can," the governor added.