What You Should Know About Influenza B


Influenza B doesn't get the attention Influenza A does. There's sometimes 1 strains, sometimes 2 B strains in a vaccine. There's always 2 Influenza A strains in each vaccine.

There's a reason for this. Flu B has never caused a Pandemic. Flu A has. Flu B is, in fact, never expected to cause a Pandemic because of the way it mutates.

That doesn't mean Influenza B should be overlooked. It can cause severe illness.

It might also be making a comeback. 2015 has seen a lot more Influenza B than normal - that is, in the Southern Hemisphere, in Australia.

Usually about 1 in 4 flu infections are caused by A; the rest of flu infections that are typed are caused by A.

The most important thing to do is to get the Influenza Vaccine to protect yourself. There are many types of flu vaccines. It's important not to delay looking for one type, but to be vaccinated with what is available and feasible (as long as you do not have a history of allergies or a medical condition that would preclude using this vaccine).

So if Influenza B doesn't cause pandemics because it mutates differently, then:

How does Influenza B mutate?

Influenza B undergoes slow mutations. It does not suddenly shift like Influenza A. This means it doesn't suddenly surprise our immune systems with a brand new virus that we - and others around us - can't handle.

When Influenza A surprises us - and our communities all at once, we're at risk for epidemics, even pandemics. 

Influenza A also spreads among many animals, especially farm animals and migratory birds, which have different immune systems leading to different strains and which are able to spread the virus far, through farm market trade and flight.

Mixing and matching between different species can create a lot of different combinations of viruses, which can be particularly scary sometimes.

But can Influenza B still make you sick?

Yes. It can.

Most cases of Influenza A and B cause a self-limited disease with

  • Abrupt fever
  • Chills
  • Headache
  • Cough
  • Sore throat
  • Muscle aches

The disease usually affects the upper respiratory tract, rather than being more serious and affecting the lower respiratory tract. Some do have more complications including pneumonia (lower respiratory tract disease), inflammation of muscles, heart, or even brain, which can be very serious.

Children usually have more varied symptoms. They are more likely to have serious complications, like encephalitis, which is seen more in Influenza A, though very rare in both. They may also have seizures when they have a fever, which can be scary for parents. They often have loss of appetite, stop eating, have diarrhea, and vomitting. They may have bronchitis or the croup or other lung infections.

Influenza B can give some children severe muscle cramps so that it was hard to walk.

Do we expect to see Influenza B this year?

At the end of the flu season in the Northern Hemisphere in 2014, the CDC saw Influenza B gaining ground.

The Southern Hemisphere, where the flu spreads while it's quiet in the Northern Hemisphere, saw a lot of Influenza B in 2015Parts of Australia in particular saw Influenza rates rise with B late in the Flu Season.

Does the vaccine work?

Yes. The vaccine will work if influenza B in the vaccine is matched to what the strain is that is circulating. Sometimes it doesn't match. Those who are most likely to get sick are children.

Does it matter when it doesn't match?

A study looked at 1999-2012, and saw Influenza B accounted for over 1 in 4 flu infections, but that of influenza B infections at least 2 in 5 were caused by viruses not covered by the vaccine.

This means that 1 in 10 infections (and up to 16.8% of infection in 10-14 year olds) were caused by influenza B that was vaccines were not designed to protect.

When vaccines don't protect against a given strain, there's more of a chance for this strain to spread, as otherwise the vaccine (or herd immunity) helps protects us.

Why doesn't it match?

The flu vaccine always contains 2 strains to match an influenza A. The flu vaccine may contain 1 or 2 strains to cover an influenza B. Historically, it has been more important to match A than B.

That is to say, the influenza vaccine has either 3 or 4 strains and always has 2 Flu A's and either 1 or 2 Flu B's.

This year (2015-2016) the 3 strain vaccines all contain:

  • an A/California/7/2009 (H1N1)pdm09-like virus
  • an A/Switzerland/9715293/2013 (H3N2)-like virus
  • a B/Phuket/3073/2013-like virus. (B/Yamagata lineage virus)

Note the 3 strain vaccines only have one strain of B and two of A. If there is a 4th strain, it is a B strain. This year the second B strain is B/Brisbane/60/2008-like virus ( B/Victoria lineage virus).

Which vaccines have the extra B strain?

The vaccines with the extra B strain are called quadrivalent, rather than trivalent. In 2014-2015, about half of flu vaccines had 4 strains. The most important thing is to be vaccinated. You don't want to wait for a different vaccine and then get the flu because you are not vaccinated.

These vaccines that contain 4 strains are: Fluarix Quadrivalent (GlaxoSmithKline), FluLaval Quadirvalent (distributed by GlaxoSmithKline), Fluzone Quadirvalent (Sanofi Pasteur), and Fluzone Intradermal Quadrivalent (Sanofi Pasteur). Note this includes the vaccine that can be given just in the skin, the intradermal Fluzone vaccine.

The nasal spray vaccine has all 4 strains. The spray is called FluMist Quadrivalent (by MedImmune). It contains live attenuated influenza virus. 

Other vaccines include only 3 strains, including Fluvirin (Novartis), Fluzone (Sanofi Pasteur), and Afluria (bioCSL).

Those who get a special vaccine because of egg allergies will receive 3 strains. The two vaccines sometimes given to those with allergies to eggs - Flucelvax (Novartis) and FluBlok (Protein Sciences) - are trivalent. Flubok is pretty important because it does not use eggs at all, which would make it important if there were ever a pandemic needing rapid vaccine production. Flucelvax uses mammalian cells in production of the vaccines and is not grown in chicken eggs, but the virus first used in production to first seed the mammalian cells is grown in chicken eggs.

The high dose vaccine, Fluzone High Dose (Sanofi Pasteur) has 3 strains only and does not have 4 strains. It has 4 times as much of the flu antigen in each dose, but it has only 3 strains. It is often offered to the elderly who may need more flu antigen to make a strong immune response.

Are there precautions for the regular vaccine shot?

Talk to your healthcare provider if you are allergic to egg proteins or you have had a reaction to an influenza vaccine in the past, before taking any vaccine. If you are ill now or have had Guillain-Barre syndrome within 6 weeks of a prior flu vaccine, please talk to your healthcare provider about this.

Read more here about the nasal spray.

Again, as long as you do not have any medical or allergic contraindications, it's important to be vaccinated for the flu - and not to wait to find a particular type of flu vaccine if it's not easily available.

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