Déjà Flu- Get a Shot, or Not?

I’ll be honest with you: the 2014-2015 flu season doesn’t look like a fun one. Unlike Ebola, the influenza virus is really good at its job (which is, essentially, reproducing). And although it tends to get less media coverage, you should be far more worried about the flu virus than Ebola. At the time of this post, there have been 2 total cases of Ebola contracted in the US, both of whom survived; but 7 children have died already this year because of influenza (note that this number includes only children, and the season is just starting). I’ve had several patients with flu already, and if predictions are right, I’m going to see a lot more. Here’s an update on this year’s flu season, along with some information about the virus and the vaccine.

 

What is “the flu?”

“Flu” is short for “influenza,” a virus that causes fever, body aches, cough, vomiting, and a variety of other symptoms. The name often causes confusion because it is sometimes used loosely to refer to colds or the “stomach flu” (both of which are caused by unrelated viruses). Typically, symptoms caused by influenza are more severe, occur more suddenly, and last a bit longer than other viruses.

How dangerous is it?

Usually, not very dangerous. Most healthy adults or older children will will terrible and miss a few days of work or school. But for children under 2, elderly people, or people with weak immune systems or chronic health problems, it can be deadly. Every year, thousands of people die from the flu or complications from it.

How do you get the flu?

The flu virus is transmitted by respiratory droplets when people cough, sneeze, or talk. You can also pick it up by touching contaminated surfaces. The flu virus is very contagious, and you can become infected even from several feet away.

How can I keep from getting the flu?

Your best bet is avoiding being around people that have it. But you don’t always know when people have the flu (and they might not either—people are contagious about 24 hours before they develop symptoms), so that can be tricky. And if you’re like me, and work in a hospital full of germ kids, it’s just not possible. Good hand-washing is crucial, and the flu vaccine can be helpful, too.

I got a flu shot last year; do I really need another one?

Alright, here’s where it gets tricky. The simple answer is yes. If you want to know more, keep reading.

Unlike a lot of things that we immunize against, the flu changes all the time. It’s evolution on a microscopic scale. This complicates things for your immune system, which does its job by making antibodies to “antigens” on the virus particle. Two of the main antigens are hemagglutinin and neuraminidase. (This is where the “H” and “N” in the names of different flu strains come from.) The flu virus replicates by making thousands of copies of itself from its genetic blueprint, but it isn’t perfect. Sometimes the new virus is just a little different. Over time, the differences add up and can prevent your immune system from recognizing the virus. These slow changes are known as “antigenic drift.” (Think of this as wolves being bred over time to become Great Danes and Yorkies—they came from the same ancestor, but don’t look much alike.)

Another type of change in the virus is called “antigenic shift.” This is a more sudden change and requires a person or animal to be infected with two different strains of flu virus. As the two different viruses make copies of themselves, some of the pieces get mixed up. (Going back to my dog example, this is like a Rottweiler head on a Dachshund body—and it can really throw your immune system for a loop.) This is what happened with the 2009 H1N1 virus, and why that year was such a bad flu season.

These changes are the reason that you can get the flu more than once (unlike, say, chickenpox or measles). They are also the reason that a team of researchers is tasked every year with predicting what the most common strains of flu will be, so that vaccine manufacturers can make the next year’s flu vaccine. I don’t envy that job; it’s a bit like predicting the weather for a football game 6 months in advance, except that if you get it wrong, people die. The vaccine companies then take the top 3 or 4 strains that are predicted to be circulating and start cranking out vaccines (and praying they got it right).

So, did they get it right this year?

Well…not so much. One of the major strains of influenza circulating this year is a strain of H3N2 that has “drifted” from the strain included in this year’s vaccine. About 52% of the circulating H3N2 flu is different enough that your immune system might not recognize it, even after the flu vaccine. That’s not great, but the vaccine still provides protection against several other strains and may offer partial protection even against this drifted strain.

I heard the flu shot can give you the flu.

You heard wrong. There are two types of vaccines—intramuscular (the shot) and intranasal (the nasal spray or FluMist). The intramuscular vaccine contains flu virus particles that have been killed, or “inactivated.” It cannot give you the flu. The nasal spray does contain a live virus, which is “attenuated,” or made weaker. It can cause some mild symptoms like fever or congestion, but nothing like getting the flu.

Which type of vaccine should I get?

For healthy children between 2 and 8 years of age, the intranasal vaccine has been shown to provide more protection, so unless they have a medical problem that prevents them from getting a live-virus vaccine, it’s the better choice. It makes sense that the intranasal vaccine may provide more protection for other people as well, but there’s not enough evidence to say for sure. Some people prefer the shot because it doesn’t make them feel crummy for the next day or two; some prefer the nasal spray because they don’t like needles. It’s your call. Just pick one.

How effective is the flu vaccine?

That’s the big question—does the flu vaccine work? Unlike other vaccines, we actually don’t have a ton of evidence to go off of. The flu vaccine’s effectiveness also varies from year-to-year because of the reasons I discussed above. But according to reviews by the Cochrane Collaboration (probably the best medical evidence you can find), you can prevent 1 case of flu in adults by vaccinating about 40 people. The numbers are better in kids (you can prevent 1 case with 6 live nasal vaccines or about 20-30 killed-virus shots). Overall, the flu vaccine is not nearly as effective as most of our vaccines, and if it cost thousands of dollars or had high complication rates, my opinion would be different. But at about $25 each and with pretty minimal side effects, it’s almost universally accepted to be worth it.

How is the flu treated?

For people who test positive for flu, there are two medications (Tamiflu and Relenza) that specifically fight the flu virus. These medicines work better when given very early in the illness (within a few hours after symptoms start), and really don’t do much at all after 48 hours. They are also effective for preventing flu in family members or close contacts of people known to have flu. The evidence for their effectiveness isn’t great, and they have a pretty high rate of side effects; there’s a lot of debate about whether they are worth using. If the symptoms have been present for longer than 48 hours, we treat flu like any other virus: rest, fluids, Tylenol or ibuprofen, etc.


For more information than you ever cared to know about influenza, including detailed current information about circulating strains, check out the CDC’s website or flu.gov. If you have any questions about the flu virus or the vaccine, any comments about the effectiveness of Tamiflu, or any anecdotes about a cousin who got the flu from a flu shot (he didn’t), please leave them below. And as always, if you’re concerned for your child’s health (or your own), call your doctor.