Nurse Mary Ezzat delivers a Pfizer COVID-19 booster syringe to Jessica M. at the UCI Medical Center in Orange, Calif., Thursday, August 19, 2021.

Jeff Gritchen | MediaNews Group | Orange County Register via Getty Images

Nearly 1 million Covid-19 vaccine booster shots have been given in the U.S. since health officials approved additional shots of Pfizer or Moderna vaccines to people with compromised immune systems on Aug. 12, according to the Centers for Disease Control and Compiled Prevention Data.

Around 955,000 fully vaccinated people received an extra dose of a Covid vaccine, CDC data shows. That number includes those who previously received two doses of Pfizer or Moderna vaccines or one dose of Johnson and Johnson, the agency said.

It is unclear whether all of these people were considered to be immunocompromised.

In approving booster vaccinations in people with weak immune systems – who include cancer, HIV patients, and organ transplant patients – CDC officials cited several small studies that showed that after two doses of Pfizer or Moderna vaccines they did not produce adequate immune responses. Food and Drug Administration and CDC officials didn’t approve booster doses of J & J’s vaccine earlier this month, saying they would wait for more dates.

Some Americans found ways to get additional doses of the Covid vaccines themselves even before formal approval. Some even went so far as to get the additional footage from different companies – a practice known as “mixing and matching”.

The CDC and FDA are considering whether to give booster shots to the general population.

President Joe Biden said the US plans to distribute Covid booster vaccinations on a large scale in the week of September 20 pending approval from FDA and CDC scientists.

The CDC Advisory Committee on Vaccination Practices debated the need for boosters Monday, saying the data showing widespread use is limited.

Dr. Helen Keipp Talbot, a voting member of the CDC advisory group, told the committee that many hospitals in the south are already giving third doses to health workers and patients.

New Jersey officials said Monday that more than 36,000 additional doses were given to immunocompromised health care workers and frontline seniors. State health commissioner Judy Persichilli said the state is trying to identify more people who will qualify for a third dose.

“We estimate 3% of the population nationwide is immunocompromised, so we are asking long-term care medical directors in particular to do a thorough analysis of these medical records and identify people who should be queued to get the third dose properly get now, “said Persichilli.

– CNBC’s Bob Towey and Nate Rattner contributed to this report.