Last year was the worst season for influenza mortality in decades

A couple of days ago, I wrote about “Vaccine Injury Awareness Week,” a fake “awareness” week made up by the grande dame of the antivaccine movement, Barbara Loe Fisher, founder of the National Vaccine Information Center (NVIC) and über-quack Joe Mercola. In their rant about wanting to increase “awareness” of vaccine injuries, which to them and other antivaccine activists, seems to encompass everything from autism, to sudden infant death syndrome (SIDS), to shaken baby syndrome (which to some antivaxers is a misdiagnosis for “vaccine injury”), to autoimmune diseases, to diabetes, to asthma, to…well…just about everything, they attacked the influenza vaccine as ineffective and dangerous. More importantly, they dropped a common antivaccine trope that influenza isn’t that big a deal, that it isn’t a major public health problem. They cited the usual antivaccine misinformation, misrepresenting the “assumptions” that are used to estimate influenza mortality, which in recent years has been estimated somewhere between 12,000 and 56,000 people die of influenza or influenza-related complications every year. The idea, of course, was to portray the yearly public health campaign to persuade people to get their flu vaccines as unnecessary and a product of big pharma trying to make money.

So the timing of this announcement from the Centers for Disease Control and Prevention (CDC) is rather unfortunate for the NVIC and Joe Mercola. Reported in various news outlets, including the AP, the CDC estimates that 80,000 people died of the flu or its complications last year:

An estimated 80,000 Americans died of flu and its complications last winter — the disease’s highest death toll in at least four decades.

The director of the Centers for Disease Control and Prevention, Dr. Robert Redfield, revealed the total in an interview Tuesday night with The Associated Press.

Flu experts knew it was a very bad season, but at least one found the size of the estimate surprising.

“That’s huge,” said Dr. William Schaffner, a Vanderbilt University vaccine expert. The tally was nearly twice as much as what health officials previously considered a bad year, he said.

In recent years, flu-related deaths have ranged from about 12,000 to 56,000, according to the CDC.

This figure jibes with the impression I’ve heard from a lot of my colleagues in internal medicine, who tole me last year that admissions for the flu and complications due to the flu, were much higher than usual last flu season. As the CDC notes, one reason the flu season was so severe last year was because that it was driven by a strain of flu (influenza A virus H3N2) that tends to put more people in the hospital and cause more deaths, particularly among young children and the elderly.

It also didn’t help that last year was one of the years when flu vaccine efficacy wasn’t that great—at least not against H3N2, the most dangerous strain in circulation last year. Canadian researchers earlier this year reported in Eurosurveillance that the H3N2 component of the vaccine had dismal efficacy:

Their midseason estimate, based on data from the four provinces where roughly 80 percent of Canadians live, suggested that the H3N2 component of the vaccine is 17 percent effective at preventing infection. Last year it was estimated at 37 percent in Canada and 34 percent in the U.S.

Public health authorities have come to expect protection against H3N2 — the weak link of the vaccine — to be in the low-to-mid 30 percent range at best. But this estimate is half that. And the fact that it was so much lower came as a surprise to the Centers for Disease Control and Prevention’s flu experts, who have yet to analyze their midseason flu vaccine effectiveness data.

“It was lower than what the Canadians or we experienced last year,” said Alicia Fry, head of epidemiology for the CDC’s influenza division. Given that there haven’t been major changes in the viruses, “it is a surprising result.”

Granted, the study had relatively low numbers of people and the estimates for efficacy against the various strains had wide confidence intervals, but it was a disappointing result. The CDC’s own estimate of the overall effectiveness of last year’s flu vaccine was 36% and 25% against the H3N2 strain. As I said before, last year the flu vaccine wasn’t that great, at least not against the worst strains. (Effectiveness against H1N1, for instance, was 67%.)

The CDC’s going to have to update its summary of the 2017-2018 flu season, it appears, given that there’s no estimate of influenza mortality and the total death toll. There is, however, this:

As of August 25, 2018, a total of 180 pediatric deaths had been reported to CDC during the 2017-2018 season. This number exceeds the previously highest number of flu-associated deaths in children reported during a regular flu season (171 during the 2012-2013 season). Approximately 80% of these deaths occurred in children who had not received a flu vaccination this season. For the most recent data and more information visit FluView: Influenza-Associated Pediatric Mortality.

Since flu-associated deaths in children became a nationally notifiable condition in 2004, the total number of flu-associated deaths among children during one season has ranged from 37 (during the 2011-2012 season) to 180 (during the 2017-18 season, as of August 11); this excludes the 2009 pandemic, when 358 pediatric deaths from April 15, 2009 through October 2, 2010 were reported to CDC.

Yes, children die from the flu, antivaxers. They do, no matter how much you try to deny it. So do adults, a lot of adults.

Of course, I can easily predict that antivaxers will try to downplay this estimate of 80,000 deaths from the flu last year. Just like Mercola and Fisher, they’ll try to claim that, because the estimate isn’t strictly an estimate of people who die with “influenza” listed as the cause of death on their death certificate and a laboratory-verified influenza infection. The CDC specifically answers this question:

Seasonal influenza may lead to death from other causes, such as pneumonia, congestive heart failure, or chronic obstructive pulmonary disease. It has been recognized for many years that influenza is underreported on death certificates and patients aren’t always tested for seasonal influenza infection, particularly the elderly who are at greatest risk of seasonal influenza complications and death. Some deaths – particularly among the elderly – are associated with secondary complications of seasonal influenza (including bacterial pneumonias). Influenza virus infection may not be identified in many instances because influenza virus is only detectable for a short period of time and/or many people don’t seek medical care until after the first few days of acute illness. For these and other reasons, statistical modeling strategies have been used to estimate seasonal flu-related deaths for many decades. Only counting deaths where influenza was included on a death certificate would be a gross underestimation of seasonal influenza’s true impact.

I like to go back to Mark Crislip’s discussion of influenza mortality and why it’s hard to estimate excess mortality from influenza, starting with the common estimate of 36,000 deaths a year from influenza:

36,000 is a lot of people. That’s about 120 deaths per million people in the US. In Oregon, population about 3 million, that would be about 360 people a year, which is two deaths a day for the six month flu season.

2,400,000 people die every year in the US, about 6600 a day. In Oregon, that is about 65 deaths a day. No one outside a epidemiologist is going to notice 2 extra deaths a day during flu season. I have seen a lot of people die of influenza, but I have a biased experience: I am an infectious disease doc, so I am likely to see people with influenza, especially patients with disease severe enough to kill them.

About the same number of people die from car accidents and die from handguns in the US each year as die from influenza. I have never known a person in my real, as opposed to my professional, life to die from influenza or handguns or a car accident. My personal experience suggests no one dies from these causes, but since I take care of patients at one of the Portland trauma hospitals, I know what cars and guns do to people. My professional life confirms that people do indeed die from being shot or car accidents. I would wager that most people reading this blog have not known anyone who has died from influenza, guns or car accidents.

Mark’s probably right about most people not knowing anyone who died of the flu, handgun, or a car crash, but I can’t help but note that I’ve known people who’ve died from two out of these these three causes. A friend of mine from college died in a car crash, and I knew someone who ultimately committed suicide. However, I have never personally known anyone who’s died of the flu or its complications. The point still stands, though, and the example described by Mark illustrates why statistical modeling is needed to estimate the number of deaths due to the flu. Of course, like climate science denialists who don’t trust climate models and dismiss them as so hopelessly flawed as not to be believed, antivaxers dismiss the epidemiological statistical models used to estimate influenza mortality. They don’t understand the models; so they dismiss them.

In any event, I have a word for Barbara Loe Fisher, Joe Mercola, and all the antivaxers out there trying to claim that influenza is not that big a deal, that it’s not a major public health threat, that the CDC and public health officials are intentionally exaggerating the death toll in order to sell you vaccines every year: You’re full of crap.

Get your flu vaccines, everyone. Yes, the influenza vaccine is highly imperfect, but it’s the best we have and will remain so until a universal flu vaccine is finally developed, tested, and shown to work.