3 reasons why Influenza B/Victoria is disproportionately preying on younger adults this year.
It’s about to be 2020, and a lot of people are starting out a new decade sick on the couch.
You have probably heard that this winter’s flu season is off to an early start. And you may have learned that — in unusual fashion — Influenza B is leading the attack. And now after some busy ER shifts, I can tell you that patients aged 20–39 are the ones most commonly getting sick.
Take a look at all the red states on the CDC map:
Sure, some old folks are getting sick and babies are being hospitalized. But compared to the last decade of flu seasons, young adults are disproportionally getting sick. Why?
Reason 1: Flu B/Victoria jumped the starting line this year
Bear with me for a few lines about the viral arms race…
Most seasons the bad actor is Influenza A, with strains H1N1 and H3N2 being well known and headline-worthy strains. Flu A is a big challenge for vaccine manufacturers because it mutates very quickly and makes vaccine selection a bit of a black art. Not so with Influenza B; flu B is the less clever virus and it does not change much from year to year. Usually, Flu B shows up late in the season (after a lot more folks have been immunized) which dampens its impact.
Not this season. Instead, flu B got started months before it was supposed to. Did you want a flu shot for Christmas? Have a New Year’s resolution to get a flu shot? Flu B is weeks ahead of you, which brings me to point #2.
Reason 2: Millennials are invincible and don’t get the flu shot
Well maybe not invincible exactly, but millennials tend to be healthy young people with healthy habits. Plus, they hang out with other healthy young people thus avoiding exposure. Why would they need a flu shot? (Honestly, I might not get one if I wasn’t on the frontline of healthcare)
Millennials are busy, and getting a flushot is not on the top of their todo list. They are statistically unlikely to have a primary care doctor and they might not have insurance, both of which reduce the opportunity to get vaccinated. In other words, young adults (anyone aged 13–40something) have low influenza vaccination rates.
Combine low vaccination rates with the early flu season and put all those viruses and young people together on airplanes for Thanksgiving/Christmas travel and you have a recipe for a bad flu season.
Reason 3: Shh, here’s a secret: A lot of young people are flu virgins
Meanwhile, Grandma and Grandpa have been around the block a few times.
Seniors have seen decade after decade of flu seasons, so their immune systems know the Victoria strain of Influenza B from back in the day. And Grandma or Grandpa go to the doctor a lot more, so they’ve been immunized against Victoria multiple times in the past. (disclosure: the science of immunity is pretty complex, and I’ve oversimplified it here)
“But I’m not a flu virgin, I totally had the flu two years ago and this flu is way worse!”. Totally possible, but if you didn’t have a lab-confirmed case two years ago, I don’t necessarily believe you. Maybe you had a really bad cold, maybe you had the flu, but we cannot know for sure. What I do know is that about 75% of patients that think they have the flu do not have the flu when tested. Those seventy-five percent of people who think they had the flu before are in for a miserable reality check when they get real influenza. Check this CDC graph:
Note that the y-axis is labeled influenza-like illness. Of the ER patients coming in for flu-like symptoms this week (all of whom were 100% miserable), only 22% of those patients tested had lab-confirmed influenza. (of which, 70% were flu B, 30% flu A)
Regardless, the graph shows that this season is tracking towards being the worst flu season of the decade.
What to do?
Avoid sick people. Really, prevention is the best medicine.
Stay home when you get sick. You don’t want to be that guy at the office.
And plan to stay home for at least a week. The miserable symptoms seem to be lasting 6–10 days this year.
Lastly, decide whether the flu shot is right for you. (My discussion on who should get the shot is here) It is not too late to get one. Current surveillance shows that for flu B, the vaccine matches 58% of the B/Victoria samples and 100% of the B/Yamagata samples.
Influenza A? Flu A hasn’t even started to hit its stride yet, and I promise you don’t want it either. Early data suggests that while the vaccine is only a 34% match for H3N2, it is 100% matched to this season’s emerging H1N1.