Ask Dr Gary: Let doctor decide on shots

I was in a car accident recently and received a cut on my head which was stitched up in the emergency room. A friend said I didn't need a tetanus shot because I was a tetanus "graduate". Her doctor told her that people in their 50s would never need another tetanus shot because they'd had so many already. I did get a shot, but was it necessary? - Marie

Your question interested me, because I'd never heard of anyone being a tetanus "graduate," or of lifelong immunity against tetanus. But with a bit of digging I was able to find out more.

It boils down to that "expert opinion" on who needs tetanus booster shots varies widely.

The death rate from tetanus ranges from less than 10 per cent in Western nations to more than 60 per cent in parts of the developing world. About 200,000 cases occur worldwide in infants alone, mostly in Africa and India, where it's not uncommon for rural people to smear cow manure or ashes and burned soil on newborns' umbilical stumps.

Many more cases occur in those exposed to tetanus spores, which are common worldwide in soil and manure, and that take hold in deep wounds, puncture wounds, burns and wounds that fester.

Punctures from rusty nails are a common mechanism for tetanus, not because they carry more tetanus spores than other surfaces, but because they provide a perfect tetanus delivery method: a deep puncture with foreign material, rust, and in a part of the body with very poor bloodflow, the feet.

A cut on the scalp is usually the opposite: lots of bloodflow and not very deep.

In New Zealand, children are supposed to have five tetanus shots by age 11, and adults should get booster shots at ages 45 and 65. There is a need to be vigilant in patients with dirty wounds or wounds with devitalised tissue in them, and in wounds sustained by people who have had fewer than three tetanus shots.

These people will need an injection of tetanus immune globulin - actual antibodies from another person - rather than just a tetanus vaccine.

Bottom line: if you have a wound that is dirty, deep, or devitalised, get a doctor to figure it out.