Flu season will soon be upon us in the Southern hemisphere. So let's consider whether it is worth getting a flu vaccine. There is not a clear scientific consensus on this. The US Centers for Disease Control (CDC) enthusiastically recommends that everyone gets vaccinated, but the prestigious Cochrane Collaboration has published several reviews which are cautious of the vaccine's benefit.

How the vaccine works

The influenza virus mutates continuously. Every year, research laboratories try to develop a flu vaccine that is effective against the most prevalent strains of influenza for the current season. The vaccine injection offered at your local pharmacy typically consists of three killed flu viruses. The 2010-2011 vaccine, explains the CDC, "will protect against 2009 H1N1, and two other influenza viruses." The benefit of the vaccine depends on scientists correctly estimating the most prevalent flu strains.

It takes a couple of weeks for the vaccine to become effective after it is injected, so if you intend to get vaccinated try to do so by April if not earlier because influenza infects most people during autumn and winter.

What does the evidence show

Cochrane reviews of medical evidence use a well-established methodology and are the gold standard for deciding the benefits of particular medical interventions. I found Cochrane reviews of the flu vaccine in nine different types of people. The results are generally not compelling. This is the conclusion for flu vaccination in healthy adults:

The combined results of these trials showed that under ideal conditions (vaccine completely matching circulating viral configuration) 33 healthy adults need to be vaccinated to avoid one set of influenza symptoms. In average conditions (partially matching vaccine) 100 people need to be vaccinated to avoid one set of influenza symptoms. Vaccine use did not affect the number of people hospitalised or working days lost but caused one case of Guillian-Barré syndrome (a major neurological condition leading to paralysis) for every one million vaccinations. Fifteen of the 36 trials were funded by vaccine companies and four had no funding declaration. Our results may be an optimistic estimate because company-sponsored influenza vaccines trials tend to produce results favorable to their products and some of the evidence comes from trials carried out in ideal viral circulation and matching conditions and because the harms evidence base is limited.

In a nutshell, there is evidence of benefit, but don't get too excited.

For healthy children, the conclusion is more promising:

The review authors found that in children aged from two years, nasal spray vaccines made from weakened influenza viruses were better at preventing illness caused by the influenza virus (82% of illnesses were prevented) than injected vaccines made from the killed virus (59%). Neither type was particularly good at preventing 'flu-like illness' caused by other types of viruses (33% and 36% respectively).

But for children under two the efficacy of the killed virus vaccine was similar to placebo. The review also found that there was very little information on the safety of vaccines administered to under-twos.

For the elderly:

Due to the poor quality of the available evidence, any conclusions regarding the effects of influenza vaccines for people aged 65 years or older cannot be drawn. The public health safety profile of the vaccines appears to be acceptable.

A Cochrane Review of the flu vaccine for people with chronic obstructive pulmonary disease found benefit, but reviews for people with cancer, asthma and cystic fibrosis concluded that there was too little research to reach hard conclusions.

What about people with HIV

We usually think of flu as a minor illness, but it actually can be very serious; it kills many people every year. Unfortunately it is difficult to estimate this accurately in South Africa, because Stats SA records influenza and pneumonia deaths together and so we can't separate these two types of death from each other. In 1997, there were under 25,000 recorded influenza and pneumonia deaths. This rose to 55,000 by 2001. (Source: Stats SA P0309.3) This was mainly due to the HIV epidemic and partially due to improved death registration.

I know of two clinical trials of the flu vaccine in people with HIV. One small study was conducted in 1999 on US veterans with HIV and found benefit. A more recent double-blind randomised controlled trial was conducted in Johannesburg on over 500 people. The vaccine reduced laboratory confirmed influenza infection by 75%, but there was no significant difference in symptomatic illness between the two groups. The researchers concluded that the vaccine was safe and effective.

So what should you do?

I am not an expert on the flu vaccine and it is possible I have left out important data. The risk of a serious adverse event from the flu vaccine exists, but is very small indeed. The CDC explains that if you have ever had a severe allergic reaction to eggs or to a previous flu shot or have a history of Guillain–Barré Syndrome after receiving influenza vaccine you should not get vaccinated.

Overall, the evidence shows a small but clear lower risk of flu for most people who get vaccinated. Personally, I prefer to get vaccinated. Whether you think it's worth the money is another matter. Some public health facilities offer flu vaccines free. It is worthwhile vaccinating children over two.

But avoid this!

My local pharmacy charges R65 for the conventional scientific flu vaccine. About a year ago, another pharmacy near me was offering homeopathic flu vaccines (they've stopped now). These do not have any active ingredients and therefore cannot be of any benefit beyond the placebo effect.

Homeopathic flu vaccines for children are marketed online in South Africa. A website offers a homeopathic vaccine called Baniflu for R91, which is R26 more than the real vaccine. This is a waste of money. People conned into this nonsense will be wasting their money. Moreover they might not get their children vaccinated with the real thing because they will be under the false impression that their children have been vaccinated.