Safety of the BCG Injection

The BCG vaccine is an effective method of immunising against tuberculosis in many parts of the world. The disease itself is highly contagious and suffers a mortality rate of about 50% for people suffering from the active infection. Treatment for BCG is effective, but lapses in the required long term dosage of antibiotics have given rise to highly virulent drug resistant strains of the vaccine. Prevention is becoming increasingly important as drug resistant tuberculosis spreads, and in this article we look at the safety of what is, at the moment, the key method of immunising against BCG.

What are the side effects of the BCG injection?

BCG can actually boast being one of the most widely used vaccinations in the world, and one with possibly the most pristine safety record in terms of adverse reactions reported. The vaccine remains closely monitored across the world to ensure its continued safety, and in the UK the Yellow Card system allows for any adverse effect to be recorded and taken to account when evaluating the safety of the vaccine.

The BCG vaccine is known to be mildly painful when compared to other vaccines, and it does cause a characteristic scar where the injection has been administered. These scars are called keloids, and form as the skin repairs itself after the injection.

For safe administration the vaccine must be delivered intradermally (into the skin) and not under the skin (subcutaneously). If the latter technique is used, there is a chance of a local infection which can spread. This occurs very rarely but should be considered when vaccination is being administered.

BCG is a live, attenuated vaccine made up of a weakened strain of the bacterium causing tuberculosis. Because a live bacterium is part of the vaccination, there are some safety considerations that are worth mentioning. Firstly with all live vaccines there is a slight risk of reversion, which means that the bacterium used in the vaccine can undergo a genetic change which would make it virulent and dangerous to human beings. This has not occurred with BCG to date, however it is still a possibility.

Live vaccines offer the advantage of being able to confer immunity after as little as a single dose, and this is the case with the BCG injection. This is because the live pathogen can stimulate a widespread and lasting immune response, and while an advantage in many cases, it does pose a problem in some cases, most notably where a person falls into one of a number of at-risk categories.

For these reasons BCG can’t safely be given to immunocompromised patients in whom even the weakened tuberculosis bacterium can cause a serious and lasting infection. Sufferers of HIV for example, bear a weakened immune system that would not be able to adequately defend itself and develop an immunity against live bacterium.

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