Despite the recommendation from U.S. health authorities to halt the use of the Johnson & Johnson/Janssen Pharmaceuticals vaccine, the national inoculation campaign will not be disrupted all that much thanks to earlier moves to secure a massive supply of two other vaccines, the White House said on Tuesday.

Earlier in the day, the Centers for Disease Control and Prevention and the Food and Drug Administration said that because of six U.S. cases of a rare and severe type of blood clotting in people who have gotten the J&J vaccine, the agencies are recommending that it stop being used for the time being. The company's shares were down nearly 3% in morning trading.

J&J is also delaying the rollout of its vaccine in Europe, where AstraZeneca's vaccine has been correlated with similar side effects.

The U.S. vaccine rollout has been humming along: According to the CDC's vaccination tracker, some 36.4% of Americans have received at least one shot of a COVID-19 vaccine, while 22.3% are fully inoculated. That translates to about 190 million doses having been administered to Americans.

But according to the White House, only 5% of those have been the J&J vaccine, which started being rolled out in the U.S. in early March, well after the Pfizer and Moderna shots did. What's more, the White House's COVID-19 response coordinator Jeff Zients said in a statement that the country had ample supply of Pfizer and Moderna—enough for the J&J pause not to have "a significant impact on our vaccination plan."

Zients added that because President Joe Biden had secured enough Pfizer and Moderna vaccines to inoculate 300 million Americans, the U.S. government's stock "is more than enough supply to continue the current pace of vaccinations of 3 million shots per day." Biden has set a goal of hitting 200 million shots by his 100th day in office, which is April 30, a target the country will easily surpass.

At the same time, J&J's vaccine requires one shot rather than the two being given for Pfizer and Moderna, which has spurred hope that its use would help to speed up the vaccination program.

While the CDC and FDA move is a recommendation, not a directive, some jurisdictions are already halting J&J vaccines. New York City Mayor Bill de Blasio, who himself got a J&J jab, said the city will immediately stop offering it until further notice, as have West Virginia authorities, among others. Anyone scheduled for a J&J shot at a New York State–run mass vaccination site today will get a Pfizer one instead, a city councilman said.

That will leave states and other partners such as cities and drugstores administering the vaccine scrambling to accommodate anyone set for a J&J vaccine to get one by Pfizer or Moderna, which also will require scheduling a second visit three or four weeks later.

In contrast to Pfizer’s and Moderna’s vaccines, the J&J vaccine does not use mRNA technology, which teaches cells to make a protein that spurs an immune response. Instead, it uses a viral vector method in which a different virus is introduced as coronavirus’s genetic material into the cells so that a person's immune system learns to recognize and fight the coronavirus.

More than 6.8 million people have received the J&J vaccine in the United States, but six have experienced the clot, the agencies said, adding that "these events appear to be extremely rare." The CDC and FDA said anyone who got the J&J vaccine and experienced symptoms including severe headache, abdominal pain, leg pain, or shortness of breath within the first three weeks should contact their health care provider.

The CDC will convene a special meeting on Wednesday to review the cases to determine how significant they are.