It's happening again: COVID-19 cases are back on the rise. There are 3 main reasons why.

COVID-19 infections continue to rise, driven by new and more infectious omicron subvariants, waning immunity from both vaccines and previous infections and fewer people masking up, health officials said at a White House briefing Wednesday.

About a third of Americans now live in an area with medium or high COVID-19 rates, with reported cases up 26% from last week, said Dr. Rochelle Walensky, director of the Centers for Disease Control an Prevention.

On average, about 3,000 Americans are being hospitalized per day and 275 are dying. Walensky urged people in communities with higher infection and hospitalization rates to protect themselves by masking in indoor public places and to get a booster shot if vaccinated and to get vaccinated if they're not.

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Areas of increased infection and hospitalization include the Northeast and the eastern corridor, as well as parts of the upper Midwest.

"We've always said, put your mask aside when infection rates are low and pick it up again when infection rates are higher," she said.

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A rising tide of omicron subvariants is in part behind the rise, said Dr. Anthony Fauci, chief medical adviser to President Joe Biden.

There are now at least four omicron subvariants circulating in the United States. BA.2 is dominant, making up 50.9% of cases but BA.2.12.1 is almost equal to it with 47.5%. The newer strains are even more infectious than previous strains, adding to the increase in cases.

He urged people who test positive for COVID-19 to reach out to their health care providers "as soon as possible" to see if a treatment is appropriate for them, as treatments work better if begun quickly.

Omicron doesn't protect against other variants

The administration's continuing push for boosters and vaccination comes as a paper published Wednesday in the journal "Nature" showed a case of omicron in unvaccinated people provides very little immunity against other variants of the virus that causes COVID-19.

"Because omicron is so infective, we were really hoping that it would help bring us closer to 'herd immunity,'" said Dr. Melanie Ott, a virologist at the Gladstone Institutes in San Francisco and lead author on the paper.

Instead, the findings showed people infected with omicron only get protection against infections from omicron subvariants, not infections from other strains of the virus. So far, there have been five main variants, alpha, beta, gamma, delta and omicron.

That's bad news for anyone who expects a recent case of COVID-19 will protect them against future cases of the rapidly mutating virus. But the good news, said Ott, is if they get vaccinated they have a shot at "super immunity."

People who've had omicron and also been vaccinated had the ability to neutralize all tested variants, not just omicron subvariants, the research showed.

"If you had omicron, why miss out on the benefit of getting that great enhanced immunity from infection plus vaccination?" she said.

Funding for vaccines & treatments

A new generation of COVID-19 vaccines are expected this fall or winter, said Dr. Ashish Jha, the White House's new coronavirus response coordinator. He and others are talking with Congress to ensure funding is available so everyone who wants them can have them.

"We do not have the resources to do that right now," he said.

Jha is on leave from his position as dean of the Brown University School of Public Health and began his new White House position in March. He said he was spending "a lot of time up on the Hill" to convince Congress to authorize more emergency aid money for COVID-19, an effort which has thus far failed as Congress wrestles with more funding for Ukraine.

The same goes for promising new treatments several companies are now working on, he said.

"No one in the United States is in negotiations with these companies for these treatments because we don't have the resources. The companies know that, and therefore we can't ensure that Americans get access to the next generation of therapies," he said.

The COVID-19 briefing was the first the White House has held in six weeks and also the first led by Jha.

This article originally appeared on USA TODAY: Why are COVID-19 cases rising and will an omicron infection protect me?