Pfizer Inc. has increased production of COVID-19 vaccines and will supply the U.S. sooner than anticipated, according to chief executive Albert Bourla on Twitter.

Bourla said the company would supply 10% more doses to the U.S. by the end of May. He said the company would deliver all 300 million doses promised for the end of July two weeks ahead of schedule.

"In the fight against COVID, we're in this together," Bourla tweeted.

The announcement came as several states suspended the use of Johnson & Johnson's single-dose COVID vaccine. The U.S. Food and Drug Administration advised them to do so Tuesday after six women in the U.S. developed a rare blood-clotting disorder that resulted in one woman's death and another in critical condition.

The Centers for Disease Control and Prevention will hold a meeting Wednesday to discuss the cases.

Some states, including New York, have reported they would use Pfizer's vaccine in place of the Johnson & Johnson shot for previously scheduled appointments.

Johnson & Johnson said in a statement that the health and safety of people who use its products was its top priority.

"This was already on our radar," Dr. Katelyn Jetelina, assistant professor of epidemiology with UTHeath School of Public Health, said

Dr. Jetelina said that when Johnson & Johnson was given emergency use by the Food and Drug Administration, they were aware of warning signs during clinical trials. However, she said that this was insufficient information to prevent the vaccine from being massively produced. In the U.S., nearly 7 million doses of the vaccine have been administered.

Despite the absence of Johnson & Johnson's vaccine, White House officials said they are on target to provide enough supplies to vaccinate the majority of American adults by the summer.

"We believe there's enough vaccine in the system - Moderna and Pfizer - for all Americans who want to get vaccinated by May 31 to do so," Jeff Zients, the White House's COVID response coordinator, said.