The 2017-2018 flu season was brutal, leading to an estimated 80,000 deaths and 900,000 hospitalizations, according to new figures released Thursday, September 27, by the Centers for Disease Control and Prevention.

Those are the highest estimated tolls the health agency has calculated for any flu season in more than a decade, the CDC noted in an email to Ars. In recent years, flu-related death estimates have ranged from a high of 56,000 (2012-2013) to as low as 12,000 (2011-2012).

Those figures are all based on mathematic modeling after the fact; exact numbers are not available, the agency notes . For one thing, states aren’t required to report adult flu deaths to the CDC. Also, many death certificates will fail to list the flu anyway.

Flu-related deaths can be the result of secondary health problems weeks after an initial infection. The virus can exacerbate chronic illnesses, too, masking the viral trigger. And sometimes patients just aren’t tested to see if they have the flu. That leaves the heavy lifting to modelers, who try to assess the full burden of the seasonal infection.

Experts had braced for such staggering figures for the 2017-2018 season. The predominant strain at the beginning of the season was an H3N2. The H3 variety viruses tend to be nastier and lead to more health complications. Moreover, early data from the Southern Hemisphere—which can offer a glimpse of what’s to come in the US—suggested that last year’s flu vaccine had an abysmal 10 percent efficacy rate.

The good news is that the vaccine in the US seemed to do better than that. The CDC estimates that it was about 40 percent effective overall during the flu season, with 25 percent efficacy against the H3N2.

The bad news is that a lot of people still didn’t get their flu shots. Early-season data estimated that only 38.5 percent of adults were vaccinated. Vaccination coverage was about 58 percent for children for the whole season, a slight decrease from the last year. About half of pregnant women didn’t get their flu shot, and a third of people who work in long-term care facilities skipped a jab, too.

The CDC wants to hammer at the disappointing vaccination coverage as it ramps up for another flu season. Even if a seasonal shot has low efficacy at completely preventing illness, it can still weaken the effects of the virus and prevent it from spreading to the most vulnerable, such as babies, children, the elderly, and those in failing health, the agency emphasizes. For instance, 180 children died of the flu in the 2017-2018 season, exceeding the most recent high of 171 in the 2012-2013 season. Of the deadly pediatric cases last flu season, 80 percent of the children were not vaccinated.

So far, the strain that looks like it will predominate in the upcoming flu season is again an H3N2, but the CDC and the Food and Drug Administration report that this year’s crop of vaccine has been tweaked to be a better match for the virus. Both agencies expect a higher vaccine efficacy and lesser health tolls this season.