(CNN) — Flu has been shown the door in the United States. Illness activity peaked and began to decline during the eighth week of the year, the US Centers for Disease Control and Prevention’s weekly surveillance report indicated Friday. Just 5% of people who visited their doctors did so while complaining of flu-like illness, down from 6.4% the previous week.
Caused by viruses, flu is a contagious respiratory illness with mild to severe symptoms that can sometimes lead to death.
“We have definitely peaked,” CDC spokeswoman Kristen Nordlund said, quickly adding, “that doesn’t mean we aren’t going to see more flu activity.”
And as long as flu continues to circulate in your community, the CDC recommends that you get a flu shot, she said.
Hawaii, Idaho, Iowa, North Dakota, Tennessee and Washington experienced low activity of flu-like illness, while Florida, Maine and Montana saw minimal activity for the week ending February 24.
Puerto Rico, California, Connecticut, Delaware, Nevada, Ohio, Oregon, Utah, West Virginia and Wisconsin all experienced moderate activity.
“You really see the West Coast and the border with Canada and a couple of places in the East are starting to see a drop in activity,” Nordlund said.
Despite the positives, the flu season is not nearly finished.
But it’s not over yet
“Where we are at now is still the peak we saw last season,” Nordlund said. Last year was a relatively mild season for influenza.
“There’s still high activity and many more weeks of flu season to go,” she said.
In fact, high flu-like illness activity continued in New York City, the District of Columbia and the remaining 32 states.
The CDC reported 17 additional flu-related deaths in children, raising the total to 114 pediatric deaths for the 2017-18 season, which began October 1. There were 101 pediatric flu deaths last season.
The season also included 23,324 confirmed flu-associated hospitalizations as of February 24. The cumulative rate of flu-related hospitalizations rose to about 82 people out of every 100,000, up from nearly 75 out of every 100,000 last week, the CDC estimated in its weekly surveillance report.
Additional information gathered on some of these hospitalized patients showed that more than half of the adults — about 67% — had at least one existing medical condition, such as heart disease, metabolic disorder, obesity and chronic lung disease, the CDC reported. Among hospitalized children, less than half — 44% — had an underlying medical condition, most commonly asthma, a neurologic disorder or obesity.
The CDC also found that circulating flu strains this season are a mix of H3N2, H1N1 and B viruses. Though H3N2 strains persisted and dominated during the eighth week of 2018, the overall proportion of influenza A viruses is declining, and the proportion of influenza B viruses is increasing. H3N2 commonly leads to more severe illness and more hospitalizations, according to the CDC.
The CDC confirmed 10,286 new infections for the week ending February 24, bringing the season total to 217,592.
Among adults, the proportion of pneumonia- and flu-related deaths declined half a percentage point to 9% of all deaths reported during the week ending February 10, the CDC reported, noting that these data are always two weeks delayed. This rate is higher than the 7.4% pneumonia- or flu-related deaths that had been anticipated for the week.
Potential vaccine changes
“It’s been a really, really mixed season,” said Richard Webby, a flu scientist who is part of the World Health Organization’s advisory board and a member of St. Jude Children’s Research Hospital’s Department of Infectious Diseases.
Looking globally, he said, “in the Southern Hemisphere, Australia had one of their biggest seasons for a number of years, which was dominated by the same H3N2 virus that we had in North America.” Yet New Zealand had a very mild season, and Europe saw a mixed bag of H1N1 and influenza B viruses in circulation. Rates of illness fluctuated by nation.
“We expect a mixed season. It’s not typically the same all around, but I think this season seems a little bit more mixed,” he said.
“It’s mostly this season there really was a problem with the virus that was circulating — H3N2 — and a less-than-ideal vaccine as well,” Webby said. In the US, an interim season report found that the vaccine was just 36% effective in preventing the flu.
Recalling reports of triage tents being set up outside emergency rooms in some American hospitals, Webby said, “when we hit these bad seasons, it highlights all the shortfalls that are there” in health systems.
Webby spoke on his return from a WHO meeting last week in Geneva, where representatives of the six collaborating centers from around the globe met to discuss the composition of the flu vaccine for use in the 2018-19 Northern Hemisphere season.
The background to the discussion this year was “understanding that the vaccine hasn’t really performed the way we would like in the last couple of seasons,” he said. “We’re still faced with this challenge, this technical challenge of getting a H3N2 to match the circulating strains.”
Most of the discussion related to the H3N2 component of the flu vaccine and one of the influenza B components, Webby said. In particular, H3N2 viruses all change when they get into chicken eggs that are used to manufacture the vaccine, so a good H3N2 match to the circulating viruses can morph into a not-so-good match. The WHO committee discussed which H3N2 strains might be less likely to change.
Next year’s Northern Hemisphere flu shot will contain a different strain of H3N2. “That particular strain, the Singapore strain, does seem to do a better job of covering circulating viruses than the one we have this year,” Webby said. “That’s assuming nothing changes between now and next winter.”
With regard to the influenza B components of the forthcoming flu shot, a new B/Victoria variant emerged at the very end of last winter in the Southern Hemisphere, so that component of the vaccine was changed, as well.
Ultimately, the WHO meeting mostly reiterated the problems with the vaccine technologies and discussed changes in how to make vaccines for flu. “Unfortunately, they all take time,” Webby said. “Until we get those systems in place, there will be continuing struggles to get the right virus match.”
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