This year’s flu season has killed more children than in any non-pandemic year on record, according to new Centers for Disease Control and Prevention (CDC) data.

A total of 172 pediatric deaths have now been reported in connection with the 2017-2018 flu season, including two that occurred as recently as mid- to late-May, according to the CDC. That number edges out the 171 deaths seen in 2012-2013, and surpasses the number of deaths recorded in all but pandemic years, which involve a global outbreak of a new influenza virus, to which most people are not immune.

“We saw just an overwhelming amount of flu in general this season. It was a very long season, with high levels of activity occurring over a prolonged period of time,” said Alicia Bird, an epidemiologist in the CDC’s influenza division. “That’s the main reason that we saw a higher number of deaths than we typically see: There’s more chances for children to be exposed to flu, basically.”

What’s more, the tally is likely to continue climbing, Bird said. “We’re at 172 now, but we do expect that number to increase because the system is one that requires some investigation for these cases,” Bird said. “We do sometimes get lagged reporting as well.”

Bird added that while the bulk of flu season has passed, it’s not entirely unusual for some disease to stick around into the summer months. One child who died from the flu in May had influenza B, a strain that tends to circulate later in the season, but Bird said all subtypes of the virus are still present in the U.S., albeit at low levels.

“There’s not a lot going on, but unfortunately it doesn’t take a lot,” Bird said. “Any time there’s flu viruses circulating we can unfortunately have this outcome.”

Prevention may be possible, however, with proper vaccination. Eighty percent of pediatric deaths occurred in children who did not get a flu shot, the CDC said, despite the fact that kids are more responsive to the vaccine than adults.

“The vaccine isn’t perfect,” Bird said. “But even with the current vaccine…getting the flu vaccine reduced the risk of death among children by half for any kids who had underlying medical conditions, and by nearly two-thirds for otherwise healthy children.” That’s far better than adult vaccine efficacy rates, which hovered around 36% this year.

With the beginning of the 2018-2019 flu season only a few months away, Bird said parents should plan to get all children older than six months vaccinated before it ramps up.

“[Even] with our less-than-perfect vaccine,” she said, “we can still bring these numbers, potentially, down.”

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Write to Jamie Ducharme at jamie.ducharme@time.com.