By Brenda Goodman, CNN

(CNN) — Flu continues to visit misery across the US, with all but four states showing high or very high levels of activity as a new virus strain called subclade K continues to spread.

By another measure – visits to the doctor for fever plus a cough or sore throat, which are common flu symptoms – the US is at its highest level of respiratory illness since at least the 1997-98 flu season, according to data published Monday by the US Centers for Disease Control and Prevention.

“This is definitely a banner year,” said Dr. Caitlin Rivers, an epidemiologist and senior scholar at Johns Hopkins Center for Health Security. “It’s the worst we’ve had in at least 20 years. We’re seeing a majority of the country is experiencing very high levels of activity, and we’re still in the thick of it.”

It’s striking to see such an intense season coming off last year’s bad flu season, she noted, as bad years don’t typically occur back to back.

Rivers said she’s not seeing data suggesting that the flu is peaking yet but notes that the CDC’s Center for Forecasting and Outbreak Analytics is seeing signs that the season may be reaching its apex in terms of intensity. We may be at or near peak week, Rivers said.

Nearly all US states were at high or very high levels of flu activity in the latest data. Montana and Vermont reported low levels of activity, while South Dakota and West Virginia reported moderate levels. Nevada didn’t report flu data this week but showed high levels of flu activity in last week’s report.

In terms of severity – how many people have been hospitalized by the flu – this season is not a standout yet. The cumulative hospitalization rate is the third highest by this point in the season since 2010-11, but that could change as more people are infected.

The CDC estimates that at least 11 million people have had the flu this season, 120,000 have been hospitalized with it and 5,000 people have died.

The agency also received another report of a child’s death, bringing the total number of children who’ve died of influenza this season to nine.

Flu vaccinations have been dropping in children, from a high of 53% over the 2019-20 flu season to 42% at the same point this season.

The new flu data came the same day the US Department of Health and Human services announced a plan to modify the childhood vaccine schedule. The changes would recommend that kids get flu vaccines after a consultation with a health care provider, a provision called shared clinical decision-making, which could make the shots harder for people to access.

“To back off on a flu recommendation in the midst of a pretty severe flu year seems to me to be pretty tone-deaf, and that’s coming off an influenza year where we had the most childhood deaths from influenza in many years,” said Dr. Sean O’Leary, chair of the American Academy of Pediatrics’ Committee on Infectious Diseases.

Shots are also down in adults, from nearly 61 million in 2019-20 to roughly 48 million this year, CDC data shows.

Rivers said she didn’t think the lagging vaccination rates were playing a role in the high volume of cases this year.

“The vaccine is not really expected to protect against infection and therefore transmission. It’s really just about preventing severe illness,” she said.

Instead, she says, the new flu strain – subclade K, which represents most viruses analyzed by labs – seems to be the reason for the intensity.

She said that strain just different enough from the flu viruses people have been exposed to in the past to get around our immune defenses.

Subclade K began to spread after strains were chosen for this year’s flu shots, which means the vaccines probably offer only partial protection against it.

CNN’s Jen Christensen contributed to this report.

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