Is This Year’s Flu Shot Less Effective?

This week in the office I’ve been hearing and on the internet I’ve been seeing reports that the seasonal influenza vaccine for 2017-2018 is less effective than expected.  My patients are anxiously asking me, “Is this year’s flu shot less effective?”

The short answer is yes, unfortunately.  Before the conspiracy theorists and anti-vaccine folks ramp up, though, I’d like to explain in a little more depth.

The vaccine is not INeffective, mind you, it still gives some protection against the flu.  However, this year’s dominant type-A flu strain is the H3N2 variety, and the flu vaccine is not as effective against this flu strain.  Even if the flu vaccine is a perfect match for a given year’s outbreak, this strain mutates very rapidly and can quickly change so that it evades the immune system.

Also, there seem to be two influenza B strains circulating.  If you got the quadrivalent (4-strain) vaccine, both type-B strains should be included.  If you got the trivalent (3-strain) vaccine, only one type-B strain will be covered.

One cool new development this year is that, for the first time, in one of the available vaccines the H3N2 component virus was grown in a cell culture rather than in eggs.  H3N2 doesn’t grow well in chicken eggs, and the antigens shift a little while growing in eggs.  This also makes it harder to get a good crop of virus and interferes with the effectiveness of H3N2 strain influenza vaccines.

While there isn’t any data (yet!) about whether cell-culture-produced vaccine virus is more effective than virus grown in eggs, they are watching carefully and research is ongoing to discover whether this method is better than growing virus in eggs.  One major benefit to using cell culture rather than eggs is that the virus can be grown much more quickly, and vaccine can be produced without having to decide 6 months in advance which strains to include.

There are a few additional things to keep in mind about this year’s flu season:

  • If you haven’t had your flu vaccine, you should consider getting vaccinated ASAP.  Vaccine will continue to be administered.  Even though flu is here, new cases will continue to develop for several more weeks.
  • If you have a chicken egg allergy, you should NOT automatically avoid vaccination.  Hives from chicken eggs is not a reason to avoid the vaccine.  If you have had anaphylaxis, angioedema or breathing problems with past vaccinations you can still be vaccinated but it should be done in an allergist’s office where they are prepared to handle possible severe allergic reactions.
  • Whether or not you’ve been vaccinated, you should take steps to protect yourself from influenza.  Wash your hands regularly.  Get plenty of sleep, drink plenty of water and take your vitamins.  Consider giving a fist-bump instead of shaking hands when you meet someone new.
  • If you develop a fever, body aches, headache and a cough which comes on suddenly, STAY HOME.  Do NOT go to work or visit with friends or family.  If symptoms are reasonably well controlled with OTC meds it may not be necessary to see the doctor.  Most healthy young people handle influenza without much trouble.  If you are short of breath, feel dizzy, pass out, have chest pain or symptoms last longer than 7-10 days, definitely contact your doctor.

It is estimated that we need to vaccinate 30-40 people to prevent one case of influenza in any given year.  This year the number needed to treat (NNT) is probably a little higher, but it’s still much better than other vaccines.  As I wrote not long ago, the brand new Shingrix vaccine has a NNT of 99 patients per case of shingles in 1000 person-years, and with Zostavax it was 435 patients.

Flu is here.  And while the flu vaccine is not as effective as we would like it to be, it is still worth getting.

QUESTION: Did you get your flu shot?  (I did!)  Are you happy you did?