"Whenever a Veteran or VA employee sets foot in a VA facility, they deserve to know that we have done everything in our power to protect them from Covid-19," said VA Secretary Denis McDonough.
"With this mandate, we can once again make — and keep — that fundamental promise."
The VA is the first federal agency to impose a mandate, a step President Joe Biden's administration had been reluctant to take until now.
The statement added that four unvaccinated VA employees had died in recent weeks.
Personnel such as physicians, dentists, podiatrists, optometrists, registered nurses and others now have eight weeks to be fully vaccinated.
Earlier this month, VA officials said more than 70 percent of the agency's 300,000 employees were fully vaccinated. The new order applies to 115,000 people, according to the Military Times.
California's order will apply to almost 240,000 state workers and hundreds of thousands more private-sector health workers, with full compliance required by August 21, according to a news release by Governor Gavin Newsom's office.
New York's order will go into effect from September 13 and apply to more than 300,000 city personnel, including police, fire fighters and teachers, Mayor Bill de Blasio said Monday.
San Franciso Mayor London Breed meanwhile said anyone hired by the city or county would need a vaccine before they can begin their job, extending the scope of a mandate on existing city workers announced last week.
The United States is in the midst of a surge driven by Delta, the most contagious variant identified to date, which now accounts for more than 89 percent of US cases, according to estimates.
Some 52,000 people are being infected everyday, according to the Covid Act Now tracker, though with 80 percent of seniors fully vaccinated, hospitalizations and deaths are not at the level of previous waves.
Hotspots include the states of Arkansas, Florida -- which accounts for almost a quarter of all new cases -- Louisiana and Missouri.
They have all lagged behind the national vaccination rate, but White House coronavirus coordinator Jeff Zients told reporters last week that these states were recently registering higher immunization rates in light of the summer surge.
Just over 49 percent of the total US population has been fully vaccinated, well below the 85 to 90 percent experts now estimate is required for population immunity.
"We're at about 67% (with prior infections counted) So we need a lot more vaccinations," tweeted Ashish Jha, Dean of Brown University School of Public Health on Sunday.
Controversy is meanwhile building over mandates.
On Monday, 57 medical groups representing millions of doctors, nurses, pharmacists and other health workers called for mandatory vaccinations for all health staff.
A recent WebMD report of 2,500 hospitals showed that about one in four health care workers have not been vaccinated, primarily nursing aides, emergency medical technicians, and nurses.
While Democratic-led jurisdictions are passing vaccine requirements, several Republican-led states have instead passed laws banning such measures, particularly in schools.
There are signs however that Republican lawmakers and officials are joining the chorus of support for vaccinations.
"These vaccines are saving lives," Florida Governor Ron DeSantis said at a news conference last week.
On Thursday number two House Republican Steve Scalise joined the chamber's GOP Doctors Caucus, a group of 18 lawmakers who are licensed medical experts, to tell Americans to "get the vaccine."
