Why You Need an Influenza Vaccine This Year

Even if you had it last year


There is not one flu.

There is not one vaccine.

There is not one who is risk-free.

Influenza has multiple species and strains. Vaccines come in different types (injection, nasal spray, or high dose) and brands. Each vaccine is designed annually to match that year's changing array of influenza strains. 

The CDC recommends almost everyone be vaccinated annually -  unless under 6 months old. Children over 6 months should receive 2 vaccinations 4 weeks apart the first time.

The CDC also reports from 3,000 to 49,000 people have died each year in the US from the flu. The vaccine reduces your chance of getting sick from the flu.

There is not just one Influenza

There are three influenza species that infect us: Influenza A, B, C.

Influenza A causes the most severe disease because it changes the most. Our immune systems can't always keep up with the variation.

Influenza A is in aquatic birds like ducks, but can be in pigs and chickens - and us humans. If a pig has two strains - one duck, one human - the viruses may mix creating new combinations. They mix-and-match Hemagglutinin (HA) and Neuraminidase (NA) but our immune systems cannot handle new combinations well. This happened when a new combination of HA and NA, called H1N1, spread in the Spanish Flu (1918) and Swine Flu (2009) pandemics. This mixing is called Antigenic Shift.

New strains can jump directly from birds to humans, as with bird flu H5N1 and H7N9.

New viruses are harder for our immune systems - if these viruses ever spread. Fortunately, they haven't spread much.

All 3 influenza species can also mutate by slow, persistent genetic changes, called Antigenic Drift. Influenza B and C are almost only in humans and don't mix and match with Antigenic Shift.

There is not just one strain in the influenza vaccine

Each year scientists in over 100 countries track these strains. The WHO recommends annually which strains should be included in vaccines - in February for the Northern Hemisphere influenza season starting in October, in September for the Southern Hemisphere season starting in April. It takes 6 months to produce enough influenza vaccine.

Vaccine effectiveness varies each year. Some years have closer and more effective matches. It is thought in 2014-5 that one strain the vaccine is trying to match, H3N2, has drifted and the vaccine will have less effectiveness against this strain. In 2015, a sudden spike in type B flu in Australia raised the concern that the vaccine didn't match the B type. Only about half of strains seen in 2014 matched the vaccine strain selected for the Northern Hemisphere (but much of the circulating H3N2 does actually match the Southern Hemisphere vaccine strain selected (A/Switzerland/9715293). The vaccine does match the other strains though and would then still reduce the chance of acquiring influenza.

Vaccines contain 3 or 4 strains, at least 2 A strains and 1 B strain.

In 2015-6, the US vaccines will 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, which is a B/Yamagata lineage virus

The 3 strain or trivalent vaccine won't contain any other strains.

The 4 strain or quadrivalent vaccine will also include another B virus: B/Brisbane/60/2008-like virus, which is a B/Victoria lineage virus.

Australia's vaccine had type B strains which covered the same lineages, but found a type B outbreak, increasing interest in the question of trivalent vs quadrivalent vaccines.

In 2014, the strains in the vaccine were:

  • an A/California/7/2009 (H1N1)pdm09-like virus
  • an A/Texas/50/2012 (H3N2)-like virus
  • a B/Massachusetts/2/2012-like virus

2013 vaccine reduced need for influenza medical care by 61%.

There is not one type of vaccine

There are two: (1) Inactivated Influenza Vaccine (IIV) from killed virus (2) Live Attenuated Influenza Vaccine (LAIV) from weakened live viruses. IIV is a shot by a needle into muscle. LAIV is a nose spray for people aged 2-49.

There is a high-dose vaccine for those over 65, whose immune systems may need a little extra.

Some should get the flu shot and not the flu spray, including those who are:

  • pregnant
  • immunocompromised (HIV, cancer) or visiting/caring for someone immunocompromised that week
  • allergic to eggs
  • a young child with asthma
  • under 18 on aspirin
  • on influenza medications in last 2 days

Those with severe medical problems (heart, breathing, kidney, liver, nervous system) should talk to their doctor about the vaccine.

For some, the vaccine might be contraindicated - anyone who had Guillain-Barré Syndrome (GBS, type of paralysis) and severe allergies to a flu vaccine or vaccine component (gelatin, eggs, certain antibiotics). Talk to your doctor. Some vaccines do not include egg. Anyone not feeling well can wait another day for the vaccine.

There are different brands of the influenza vaccine

Different companies produce different vaccine brands. They all have the same 3 or 4 strains. No nose spray contains the preservative thimerosal though this should not affect vaccine choice. All single-use pre-filled syringes are mercury-free, except Novartis Fluvirin, that removes Thimerosal used in production during purification leaving a trace (≤1 mcg mercury per 0.5-mL dose). Multi-use vials may contain small thimerosal amounts.

There are different people at risk.

Almost everyone should have the vaccine.

Those most in need:

Others at high risk with

  • Asthma, Chronic Lung Disease (COPD, Cystic Fibrosis)
  • Obese (BMI>=40)
  • Weakened Immune Systems (HIV, chronic steroid use, cancer)
  • Kidney, Liver, Endocrine (Diabetes), Blood Disorders (Sickle Cell) disorders
  • Heart Disease (Coronary Artery Disease, History of Heart Attack, Heart Failure, Congenital Disease)
  • Neurologic issues (Cerebral Palsy, Stroke, Muscular Dystrophy, Spinal Cord Injury, Epilepsy)
  • Metabolic/Mitochondrial Disorders

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