Thread by @ScienceVet2

It's flu season! Which means flu vaccine time!

TLDR/BLUF: Get your flu shot

1/

A 1-3 day period of feeling crappy (ache, low grade fever, etc) after a vaccine is not only normal, it means the vaccine is working. BUT it doesn't mean you have the flu.

2/

Vaccines are suspended in an "adjuvant" who's job is to wake up your immune system. That "waking up" feels like a brief, mild flu. What it does is let the vaccine have way less other stuff in it.

3/

"But if it makes me feel sick, why get it to prevent getting sick?"

An adjuvant reaction is 1-3 days of feeling yuck. A full on flu is 3-13 days, with higher fevers, often including vomiting, and much more aching and other symptoms.

4/

Additionally, with a flu infection, you're contagious for 1-7 days before showing any symptoms which could put family at risk. Young and old people often die (average 200k a year in the U.S.) from flu related problems. Don't kill grandma.

5/

"Wait, go back, other stuff?"

Yeah. You have to have something in the vaccine that your immune system can build antibodies to that protects you against flu. Exactly what that is can vary. For most people, they'll get a "quadrivalent intramuscular vaccine."

6/

Four strains of flu are grown in eggs, purified, killed, and a tiny number are added to the vaccine for your body to build antibodies to (the adjuvant lets you have fewer particles). For people who are allergic to eggs, there are versions grown in cell culture instead of eggs

/7

Some people (like my Dad) are allergic to dead flu! Weird, right? So until recently, he hasn't been able to get the flu vaccine even though getting the flu is dangerous for him, because he gets an anyphylactic (severe allergic) reaction to even a few dead flu virus particles.

/8

For these people there is a special recombinant vaccine that's just made with proteins from flu, not the whole virus. It's not as effective, but way better than nothing.

/9

"But what about that nose one, isn't it different?"

The nasal spray IS different. Instead of injecting you with dead flu, the nasal spray actually uses 4 strains of live flu that have been modified to be weaker and temperature sensative.

/10

So your body fights them more easily, and they can't spread beyond your nasal passages, but you get the benefit of a full immune response to an active infection.

11/

"I read something about the vaccine not being effective"

We don't have any effectivity data for this year's yet. However, even in years we're really off the mark in guessing what the active strains are going to be (like last year, 2017), it's still worth getting the vaccine

/12

Last year, the vaccine was estimated to reduce the length of a flu infection by about 40% even if you did catch it. That makes a normal week long flu less than 3 days, as well as reducing the severity of infection.

/13

"I read something about something something herd immunity doesn't work unless everyone something?"

Ah, this one. Ok, so! Yes. You don't get perfect herd immunity for a population unless you get basically everyone taking the vaccine. BUT! (And it's a big but)...

/14

That means, given there are people who can't have it, EVERYONE else has to, right? BUT that only looks at the whole population. Localized herd immunity is totally a thing! What does this mean?

/15

It means if all the members of a family get the vaccine and their baby can't, then while the whole population doesn't have herd immunity, that baby probably won't get flu because the people touching them aren't going to get it.

/16

My family has always all gotten it, because getting the flu is dangerous for Dad. Thus, Dad has very rarely gotten flu, because we're the people he's around the most.

/17

If everyone at a workplace gets the vaccine, even the guy who can't because of a compromised immune system probably won't, because he's insulated from touching people who'll have it.

/18

So. GO GET YOUR FLU VACCINE.

I repeat: GO GET YOUR FLU VACCINE. Last year was a REALLY bad year for deaths.

/19

For uber nerds like me, this year's is:

A/Michigan/45/2015 (H1N1)pdm09-like virus
A/Singapore/INFIMH-16-0019/2016 A(H3N2)-like virus (updated)
B/Colorado/06/2017-like (Victoria lineage) virus (updated)
B/Phuket/3073/2013-like (Yamagata lineage) virus

/20

Much of this information can also be found here, if you want to read it on your own from someone else: cdc.gov/flu/about/seas…

First flu death of 2018 season cdc.gov/flu/weekly/ind…

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