WASHINGTON, D.C. (AP) — The COVID-19 pandemic could get worse in the U.S. in the weeks ahead, officials said Wednesday, and more people could be advised to again wear masks indoors.

Increasing numbers of COVID-19 infections and hospitalizations are putting more of the country under guidelines issued by the U.S. Centers for Disease Control and Prevention that call for masking and other infection precautions.

For an increasing number of areas “we urge local leaders to encourage use of prevention strategies like masks in public indoor settings and increasing access to testing and treatment,” Dr. Rochelle Walensky, the CDC director, said at a White House briefing with reporters.

However, officials were cautious about making concrete predictions, saying how much worse the pandemic gets will depend on several factors, including to what degree previous infections will protect against new variants.

Last week, White House COVID-19 coordinator Dr. Ashish Jha warned in an interview with The Associated Press the U.S. will be increasingly vulnerable to the coronavirus this fall and winter if Congress doesn’t swiftly approve new funding for more vaccines and treatments..

The pandemic is now 2 1/2 years old. And the U.S. has seen — depending how you count them — five waves of COVID-19 during that time, with the later surges driven by mutated versions of the coronavirus. A fifth wave occurred mainly in December and January, caused by the omicron variant.

The omicron variant spread much more easily than earlier versions.

Some experts are worried the country now is seeing signs of a sixth wave, driven by an omicron subvariant. On Wednesday, Walensky noted a steady increase in COVID-19 cases in the past five weeks, including a 26% increase nationally in the last week.

Hospitalizations also are rising, up 19% in the past week, though they remain much lower than during the omicron wave, she said.

In late February, as that wave was ebbing, the CDC released a new set of measures for communities where COVID-19 was easing its grip, with less of a focus on positive test results and more on what’s happening at hospitals.

Walensky said more than 32% of the country currently live in an area with medium or high COVID-19 community levels, including more than 9% in the highest level, where CDC recommends that masks and other mitigation efforts be used.

In the last week, an additional 8% of Americans were living in a county in medium or high COVID-19 community levels.

Officials said they are concerned that waning immunity and relaxed mitigation measures across the country may contribute to a continued rise in infections and illnesses across the country. They encouraged people — particularly older adults — to get boosters.