The World Health Organization cited new economic research during a press conference Monday, which warns that vaccine nationalism could cost high-income countries $4.5 trillion. Universal vaccination may make it feel as though life is getting back to normal in wealthy countries, but global trade will suffer if poorer nations still have active COVID-19 transmissions, according to research from the International Chamber of Commerce.

"They will not only feel the hit but bear half the cost," said John W.H. Denton AO, secretary general of the ICC. "If you actually want to fix your own economy you're going to have to get involved in fixing the global economy and part of that is that vaccines flow globally and equitably."

Countries need to focus on the tools we already have to drive down COVID-19 transmissions, according to Dr. Bruce Aylward, adviser to WHO Director General Dr. Tedros Adhanom Ghebreyesus.

"If any country bets everything on the vaccine we're going to lose," Aylward said.

-ABC News' Christine Theodorou contributed to this report.

Dr. David Kessler, a former head of the Food and Drug Administration who is now overseeing the U.S. effort to accelerate the development, manufacture and distribution of COVID-19 vaccines, pushed back the timeline in which most Americans can expect to get vaccinated during an interview on SiriusXM’s "Doctor Radio Reports."

"We're not going to have everyone vaccinated in April, in May, right? Just not gonna happen," Kessler told the radio show's host, Dr. Marc Siegel. "We got to get over 65, essential workers. I think this is going to take us into the fall. We got to get there before next winter, and one of the things I care about very honestly, is we can't do this again.”

The U.S. outbreak may end sooner if Johnson & Johnson's vaccine is more than 80% effective, according to Kessler. But even if that vaccine is highly effective, he added, it will still take months to get priority groups, like older adults and essential workers, vaccinated.

"The bottom line is I wish I could tell you there's plenty of vaccine and we can fill all these endless amounts of appointments. We can't. It's going to take us months to have enough supply," Kessler said.

-ABC News' Stephanie Ebbs contributed to this report.

Massachusetts lifted its stay-at-home order Monday, which had asked residents not to go out between the hours of 10 p.m. and 5 a.m. and required businesses to close at 9:30 p.m.

"Vaccines are reaching residents, positive case rates and hospitalizations have stabilized; those trends are moving in the right direction," Gov. Charlie Baker said during a Jan. 21 press conference announcing the loosened restrictions. "As a result, we believe it's OK and it's time to start a gradual easing of some of the restrictions we put in place in the fall," Baker said.

Restaurants and other businesses will still be capped at 25% occupancy until at least Feb. 8, according to Baker. Gatherings are still limited to 10 people indoors and 25 people outdoors.

-ABC News' Brian Hartman contributed to this report.

The California Department of Public Health lifted a stay-at-home order for all regions statewide on Monday.

Four-week intensive care unit capacity projections for the three regions that had still been under the order -- San Joaquin Valley, Bay Area and Southern California -- are now above 15%, the threshold that allows regions to exit the order. The Sacramento region exited the order on Jan. 12 and the Northern California region never entered the order, according to a press release from the California Department of Public Health.

The move allows all counties statewide to return to the rules and framework of California's "Blueprint for a Safer Economy" and color-coded tiers that indicate which activities and businesses are open based on local COVID-19 infection rates and test positivity. The majority of the counties are in the strictest -- or purple -- tier. Individual counties may choose to impose stricter rules, according to the press release.

"Californians heard the urgent message to stay home as much as possible and accepted that challenge to slow the surge and save lives," Dr. Tomas Aragon, director of the California Department of Public Health, said in a statement. "Together, we changed our activities knowing our short-term sacrifices would lead to longer-term gains. COVID-19 is still here and still deadly, so our work is not over, but it’s important to recognize our collective actions saved lives and we are turning a critical corner."

California, home to nearly 40 million people, has the highest tally of diagnosed COVID-19 cases of any U.S. state, with more than 3.1 million, according to a real-time count kept by Johns Hopkins University.