A shot in the arm

A CONTROVERSIAL issue in Europe where doctors have long failed to agree on its effectiveness, Thai medical experts insist that the flu vaccine is the best way of preventing a nasty dose of influenza. 

The most recent vaccines offered here – the so-called trivalent vaccine – protect against three different flu viruses. Now, though, protection is being offered against four viruses, thanks to the introduction last week by Samitivej Hospital of the quadrivalent vaccine.

The shot, which is said to increase effectiveness by 18 per cent over its predecessor, is currently only offered by Samitivej Sukhumvit and Srinakarin. 

The influenza virus is comprised of three types – A, B and C – and each has a variety of subtypes that can cause the flu. Of these, type A, which includes the subtypes H1N1 and bird flu H5N1, and type B (Victoria and Yamagata) are responsible for annual influenza epidemics. Type C, while it can lead to flu, is mostly harmless. 

For more than 50 years the World Health Organisation has collaborated with scientists and policy makers on a global scale to develop a unified approach to manufacturing, testing and regulatory oversight of influenza vaccine development as well as their efficient use and distribution. 

The trivalent flu vaccine protects against two influenza A viruses (H1N1 and an H3N2) as well as the B subtype researchers anticipate will be most common during the upcoming season.

Clinical Prof Sanay Chearskul of Samitivej Srinakarin, a specialist in paediatric infectious disease, explains that the selection of the subtype of B virus to be included in the vaccine is decided at the WHO’s annual meeting on influenza by the World Health Organisation. Two such meetings are held in February and September and it is at these that the research and data on flu prevalence across the world are discussed.

The trivalent vaccine has been used for decades but its protection rate is now in decline.

Dr On-Umar Banpamia of Samitivej Sukhumvit Hospital, says that part of this is due to an erroneous prediction as to which of the major B subtypes will cause more problems in any given year as well as to a prevalence of A subtype protection.

This, she adds, has resulted in the trivalent’s efficacy sinking to 50 to 60 per cent from its 2000 high of 70 to 80per cent. 

“We discovered in Thailand some years ago that 30 to 35 per cent of the flu cases we see are caused by the B type,” she adds.

Both doctors hope that the research which has gone into producing the quadrivalent will make up for this shortfall.

The cost of the vaccine, says Dr Sanay, will be about 10 per cent higher than the trivalent vaccine though what the patient pays will depend on where he and she gets the shot. The Public Health Ministry does offer free flu shots but only for those who are considered most at risk. Right now, the quadrivalent vaccine is priced at less than Bt1,000 excluding all other fees.

Dr Sanay stresses that the shot is cost effective, pointing out that patients who catch the flu and feel so ill that they are forced to consult a doctor will be spending considerably more than Bt1,000. The shot also prevents complications such as pneumonia, bronchitis and heart problems.

In general, the flu vaccine works best among healthy adults and older children. Some older people and people with certain chronic illnesses might develop less immunity than healthy children and adults after vaccination. However, even for these, the flu vaccine still may provide some protection.

The side effects are similar to those experienced with the trivalent shot – mild fever and general feeling of malaise. Some people also suffer from soreness, redness, or swelling at the injection site. These problems aren’t serious and don’t last long. 

Patients who are allergic to eggs should refrain from having the shot as flu vaccines are made using an egg-based manufacturing process. Non-egg vaccines are available in other parts of the world but have yet to find their way to Thailand.