Folks are officially starting to freak out about this flu season. The nightly news features more terrifying tales of fatalities each day, and it all seems to get worse every week. But while it’s true that this year is a particularly nasty one—and you should absolutely be taking precautions—we’re not yet at historic levels. Let’s take a quick tour of the flu season so far.
This is the “worst” season since the 2009 H1N1 epidemic
“Worst” is kind of a meaningless word when it comes to disease surveillance. Does it mean most deaths? Most cases? Most geographic spread? The 2017-18 season is bad by all of these metrics, but it’s second only to the 2009 H1N1 season in what the Centers for Disease Control call Influenza-Like Illness or ILI. That’s the percentage of all outpatient visits in the United States (doctors visits where you aren’t hospitalized) that involve a person with a fever over 100 degrees Fahrenheit plus a cough and/or a sore throat. ILI peaked at 7.8 percent in 2009, and as of last week, we were at 6.6 percent. It’s impossible to know just how much higher that number will climb.
So it’s a year with a somewhat unusual number of flu cases, but Dan Jernigan, Director of the Influenza Division of the CDC, noted in a press call on Friday that it’s not unprecedented. Back in 2003-04, we saw a similar peak at 7.6 percent ILI. That was another year dominated by the H3N2 strain, this year’s most common flavor of the virus, which tends to produce more severe flu seasons. That’s in part because it mutates quite a lot in the eggs we use to manufacture flu vaccines. Those mutations mean we don’t build up immunity to H3N2 as well, which probably contributes to that strain appearing to be more deadly. It’s also possible that H3N2 is just inherently more intense than some other strains.
We’re seeing a big spike in flu deaths right now, but though shooting past the “epidemic threshold” sounds scary, it’s important to remember that we usually go past that point. The difference is that some years we go farther. Right now, roughly 9.1 percent of all deaths in the U.S. are due to flu and pneumonia (which is a common complication of the flu), as compared to the baseline average of 6.9 percent the rest of the year. That breaks down to 716 direct flu deaths and 2,855 pneumonia deaths, though those numbers are just estimates based on representative samples of the U.S.
The tricky thing about tracking deaths, though, is that the data collection lags. We won’t really know how many people died from the flu last week until all the related coroner’s reports are in, which can take weeks. “Sometimes, tragically, children will die outside of the hospital and those often have to have a coroner report or medical examiner report,” notes Jernigan. We know of 37 pediatric deaths so far, but Jernigan says we should expect that number to keep climbing. This season looks a lot like 2014-15, when there were 148 child deaths in all.
Most years, states end up having their own peak seasons at slightly different times of the year, but we’ve been oddly in sync this winter. “We often see different parts of the country ‘light up’ at different times,” explains Jernigan, “but for the past three weeks, the entire country has been experiencing lots of flu, all at the same time.”
Jernigan says there are some signs that activity is decreasing in a few states like California, but it’s not clear yet whether that’s a trend. No matter what, though, we’re probably only about halfway through the season.
The worst-hit age groups are usually the very old and the very young because both have somewhat compromised immune systems. That’s still largely true, but this year is notable for hitting Baby Boomers harder than normal. Jernigan thinks that’s probably due to a combination of factors. Part of it is that adults just generally don’t get vaccinated at high rates, and another is that Boomers may not have been exposed to H3N2 strains as much when they were kids. This whole concept is still being researched, but the idea is that the flu you’re exposed to as a youngun’ helps determine how you’ll react to flu for the rest of your life. People exposed to the H1N1 that circulated widely from 1918-1947 seemed to fare better when swine flu hit in 2009, but they’re struggling with this year’s less familiar strain. But Jernigan stresses that even if that’s a factor, Baby Boomers also definitely need to be better about getting their annual flu shot.
At this point in the flu season, many think it’s too late to get a vaccine. That’s not true. It is better to get your shot before the season starts since it takes a few weeks to build up immunity, but getting one part way through is still helpful. You may not be exposed to the virus for another few weeks. And although it’s true that you can still get the flu even if you got the shot, vaccination helps your body fight back, meaning your symptoms won’t be as severe. Plus, it decreases the likelihood of you being a carrier of the flu, which decreases the chances of you passing it on to, say, an elderly person who might actually die from the disease. Get the flu shot for other people, not yourself.