A woman receives a Pfizer vaccination booster shot at Eugene A. Obregon Park in Los Angeles.A woman receives a Pfizer vaccination booster shot at Eugene A. Obregon Park in Los Angeles.

If Congress doesn't approve funding for the next generation of Covid vaccines, the U.S. will have to limit them to people at the highest risk of getting seriously sick from the virus, according to a senior Biden administration official.

The official warned that the U.S. faces a surge of Covid infections this fall as immunity from the current vaccines fades. The official said that the U.S. needs more money to prevent infections from turning into hospitalizations and deaths.

Pfizer and Moderna are working on vaccines that target the omicron variant's genes. The current shots are still targeting the original strain of the virus. The vaccines have become less effective at preventing mild illness as the virus has evolved over the past two years.

The FDA is expected to make a decision on whether the U.S. should switch to the new shots for the fall vaccine campaign by early summer, with an advisory committee set to hold a meeting on June 28 to discuss the issue.

The U.S. does not have enough money to purchase the new shots for everyone in the fall, according to an official. Senate Majority Leader Chuck Schumer, D-N.Y., and Sen Romney, R-Utah, struck a deal in early April, but have yet to pass $10 billion in additional Covid funding. The Senate deal is less than the White House wanted.

We will be able to get some vaccines of the new generation, but it will be limited and only for the highest risk individuals. The elderly and people with weak immune systems are the most at risk.

The official said that Congress needs to pass funding in the next few weeks so that contract negotiations between the federal government and the vaccines makers are in an advanced stage by July. The Senate will block the money unless the White House restores Title 42, which allowed the U.S. to turn away asylum seekers during the Pandemic.

Even if the money comes through, it is not certain if the vaccine makers will be able to produce enough shots for the fall. Stephane Bancel, CEO of Moderna, told CNBC last week that it was a tight time to have tens of millions of doses ready for the fall if they didn't order supplies and start production before July.

Bancel told CNBC's Meg Tirrell that he doesn't think any manufacturer will be ready in August to fill the channel with product. The last contract for Covid vaccines with the U.S. government ended in April.

Pfizer CEO Albert Bourla told CNBC last week that the pharmaceutical giant would be ready to start manufacturing doses of its next generation vaccine as soon as it received guidance from the FDA.

An administration official said that the U.S. needs more money for testing to make sure there is enough capacity for the fall. The official said that the U.S. would be dependent on test manufacturers in other nations.

If Congress abdicates its responsibilities and does not show up with funding for the American people, it will be a tough fall and winter.