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The 2015 Influenza vaccine: clearing up the confusion.

by Dr Bob Kass - April 7, 2015

Two aspects regarding the 2015 vaccine have caused some concern and confusion within the community.

1)    The vaccine supply has been delayed as compared to previous years
2)    There are two different formulations instead of one. One contains the usual three strains of influenza virus (trivalent) and the other is a 4 strain (quadrivalent) vaccine.

To follow the discussion you need to understand a little about the flu vaccine and how it is made available to the government and the community.

The influenza vaccine has been a trivalent vaccine since the late 1970s, containing two strains of Influenza A and one of influenza B virus. Influenza A and B are distinctly different viruses and B, unlike A, does not circulate in animals, only in humans. Influenza B also tends to cause milder illness, is less diverse (mutates more slowly than A) and is not normally associated with epidemics. Immunity to influenza B is usually acquired in early life.

The influenza A vaccine is classified by surface proteins Haemagglutinin (HA) and Neuraminidase (NA). Every year WHO (World Health Organisation) provides advice on the components of the vaccine for the coming influenza season. This advice is usually provided in September for the southern hemisphere and February for the northern hemisphere. The advice is based on sentinel monitoring of laboratory confirmed influenza cases around the world.

The recommendations for the southern hemisphere were very similar for the 2013 and 2014 flu seasons and for the Northern Hemisphere 2014/15 winter and are outlined below;

Southern Hemisphere 2014
  • an A/California (H1N1) like-virus

  • an A/Texas (H3N2) like-cirus

  • a B/Massachusetts like-virus

Southern Hemisphere 2013
  • an A/California (H1N1) like-virus

  • an A/Victoria (H3N2) like-virus

  • a B/Wisconsin like-virus

Northern Hemisphere 2014
  • an A/California (H1N1) like-virus

  • an A/Texas (H3N2) like-virus (similar to A/Victoria)

  • a B/Massachusetts like-virus

For Australia, these recommendations were considered to be the “best fit” strains to protect against the circulating influenza viruses noted during the previous winter in the southern hemisphere and those in the inter-season northern hemisphere period. According to reports received from the many sentinel flu laboratories around the world there appeared to be little change in “other virus” activity and only minor adjustments to the manufacture of the vaccine were necessary.

Australian travellers were fortunate in 2014 to be able to source the vaccine in January rather than March or April, giving them the opportunity to prevent influenza as they headed off to the northern hemisphere (still in their high risk winter period). 

Unfortunately all was not good last year as we experienced a major outbreak of influenza during our 2014 season only to be followed by a similar pattern in the USA and East Asia (March 2015). There had been a “drift” in the structure of the major circulating Influenza A/H3N2 virus strain component and the vaccine, overall, proved to be only 18-20% protective! To put this in context, most years the protective efficacy is around 70 percent for the flu vaccine.

It was too late for a change to be made in the northern hemisphere vaccine for the 2014/15 winter but not too late for a change to the 2015 southern hemisphere vaccine. The only drawback was a delay in the release of the new vaccine. It would still require all the necessary regulatory surveillance and this would take time.

The 2015 flu vaccine (see below) became available in Australia during the 3rd week of March, just in time to be given to the many older Australians travelling by ship to the Gallipoli commemoration. We thank the efforts of our Australian vaccine producer for making this possible. The many influenza A /H3N2-related deaths in Hong Kong had us very worried and we believe the new vaccine will provide good protection for these travellers.

The later arrival of the vaccine is not a major concern to most Australians as our flu season starts around May and peaks in August/ September (see below). The vaccine works quickly with more than 90% of recipients producing good antibody levels within 2 weeks of receiving it. Peak levels are noted at about 4-6 weeks and wane to less than 50% by 6 months. 

The community was notified that the publicly funded government vaccine would be made available by April 20th in line with the arrival and clearance of all the different commercial brands. Those eligible for a free flu vaccine under the government funded program include:

  • those aged 65 years and older

  • pregnant women, any time during their pregnancy

  • Aboriginal and Torres Strait Islander people aged six month to under five years and 15 years and older

  • those with a medical condition predisposing them to severe influenza

  • those with a chronic illness 

Only some brands can be used in children under 9 years old. The free government flu programme uses all the main vaccine suppliers.

Southern Hemisphere 2015
  • an A/California (H1N1) like-virus

  • an A/Switzerland (H3N2) like-virus

  • a B/Phuket like-virus

Australian Influenza Surveillance Report No. 8, 2014

What is the new quadrivalent vaccine?

A quadrivalent flu vaccine has been available for only a couple of years (in the northern hemisphere) and this is the first year we have it in Australia. I have heard it referred to as the “Rolls Royce” flu vaccine on radio. This is not quite true. The flu vaccine can probably be seen as a Toyota Camry (pretty good but not a Lexus) and the quadrivalent is probably a Toyota Camry with a roof rack!  The new quadrivalent vaccine contains an extra Influenza B virus (two strains of A and two of B in total). For those who want the extra, the vaccine will be more expensive than the standard trivalent.

In 2014, of respiratory specimens tested from sentinel general practices for suspected influenza, 27 percent were confirmed as the influenza virus as opposed to many other kinds of respiratory viruses. Of these confirmed influenza cases, 86 percent were Influenza A and 14 percent were Influenza B viral infection. 

About Influenza

Influenza viruses spread person to person by droplet infection and small particle aerosol. Droplets generally travel only a smaller distance (< 2 metres) while aerosol may go further. 

The virus replicates in, and infects adjacent cells of, the upper respiratory tract.  Local mucosal immunity develops and there is a rise in serum antibodies.

Individuals are most contagious in the first 3 days after the onset of symptoms but probably shed the virus for about 5 days. A person also can be infectious the day before they develop symptoms. Those who are immune-suppressed or who have chronic disease shed the virus for longer. The virus can remain viable for hours in dried secretions before transfer to the respiratory tract. The incubation period (time between exposure and symptom onset) is 1 to 2 days.

About 1,500 Australians die from the complications of influenza every year. Most of these are over 65 years or under 5 years of age. Many have contributing health factors which make the illness worse. There are approximately 13,500 hospitalisations and 300,000 GP consultations every year in Australia due to influenza virus.

Assessment of Risk

There is constant global influenza presence but exposure risk for the individual depends on many factors such as time of travel, type of travel and activities relating to the trip. Infection rates are highest in children (likely non immunes) and the rates of severe illness are highest in those over 65 years (hence the free national immunization program for that group).

Attack rates are high in susceptible crowded populations. This can be as high as 40% in closed settings such as a school, retirement village or nursing home. Cruise ships are such a setting. 

The peak virus activity is in the winter months in temperate climates and during the dry season of the tropics and subtropics.

Prevention

The administration of an influenza vaccine to persons at risk is the most important measureto prevent influenza illness and its severest complications.

Travellers are always at risk due to increased exposure in airports, commuter transport and other crowded areas. They may be elderly and many have significant co-morbidities.

Have a flu jab and enjoy your travels!


Author

Dr Bob Kass

Dr Bob Kass is Medical Director of Globe Medical. He holds specialist qualifications in paediatrics and public health medicine and is one of Australia's pioneers in the discipline of Travel Medicine. 

Full professional biography