U.S. President Joe Biden is meeting with the chief executives of United Airlines and Kaiser Permanente Wednesday to find ways to boost COVID-19 vaccination rates in the country, the White House said.

In addition to United Airlines' Scott Kirby, the meeting includes Kaiser Permanente Chief Executive Gregory Adams, Howard University President Wayne Frederick and a South Carolina business owner who adopted a vaccinate-or-get-tested requirement for her workers, an administration official said.

Across the country, COVID-19 cases and hospitalizations are soaring in areas with low vaccination rates, mainly conservative states in the U.S. south.

United Airlines previously announced a requirement that all its U.S.-based employees must be fully vaccinated against COVID-19. Its major U.S. rivals, American Airlines, Delta Air Lines and Southwest Airlines, are encouraging employee vaccinations but not imposing them.

Biden has endorsed companies and local governments pressing more people to get vaccinated. The Biden administration is also looking into what authority businesses have to mandate vaccines, Labor Secretary Marty Walsh told Reuters last week.

"I will have their backs and the backs of other private and public sector leaders if they take such steps," the Democratic president said last week.

Speaking to MSNBC earlier, Kirby said employee response had been overwhelmingly positive, though some had opposed.

Mandating vaccines for passengers, however, would be more difficult and require U.S. government involvement, he said.

U.S. airlines have enjoyed a broad rebound in travel demand this summer, but Southwest warned on Wednesday that rising COVID-19 cases were hitting demand, a sign of the impact of the delta variant on the U.S. economy.