"We have definitely peaked", CDC spokeswoman Kristen Nordlund said, quickly adding, "that doesn't mean we aren't going to see more flu activity".
The Centers for Disease Control and Prevention said flu activity in Iowa has dropped in the past week.
"We do know that the vaccine is worth getting", Schuchat said. Most of the children who have died this winter had not received the flu vaccine.
Next year's Northern Hemisphere flu shot will contain a different strain of H3N2. "There's still time for illnesses and viruses to circulate".
So Skowronski wasn't surprised by the dismal data. This season's vaccine has only provided about 36 percent protection against flu.
"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", he said. Flu vaccine effectiveness can vary by country, and the United States flu vaccine effectiveness data has yet to be published, but the Canadian study is telling.
The latest report shows the overall proportion of influenza A viruses is declining, but the proportion of influenza B viruses is increasing. This week's CDC flu report shows that about half of people tested for influenza had an influenza B strain. And that's not easy.
The potential for error here can dramatically alter the effectiveness of the flu shot in a given season.
Scheifele said young children are vulnerable to the effects of flu because they're born without immunity to the four main strains - two influenza A strains and two influenza B strains. "Although a 30-percent chance of effectiveness is not ideal, if you told someone that a vaccine had a 30-percent chance of preventing death from a seizure, they'd jump at it". But significantly higher than the 10 percent Australians experienced this season. For one, the virus mutates as it moves through the population at a faster rate than other flu viruses - making it even harder to design a shot that matches the circulating virus. The first flu virus that someone is exposed to whether through infection of vaccination, may shape their immune system response to future infections. "What we're seeing here is a little bit more of an up and staying up".
But lately, researchers have found that there are problems with the egg-based approach that specifically relate to H3N2.
Webby spoke on his return from a World Health Organization 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.