Vaccinating babies with short needles may be causing unnecessary pain, British researchers say.

Infants may show swelling, redness and tenderness near the injection site when they receive a series of vaccinations at two, three and four months of age.

In the United Kingdom, recommendations call for wide, long needles to be used to help deliver the vaccine to the target muscle, but many doctors continue to use narrow, short needles for the injections.

A previous study showed bigger needles significantly reduced reactions at four months of age, but researchers couldn't tell what made the difference: the needle's length, width or gauge or how the needle affects delivery of the vaccine itself.

Long needles can significantly reduce vaccine reactions while achieving similar levels of immune protectionas short needles, the team concluded in Friday's online issue of British Medical Journal.

In the experiment, pediatric researchers at the University of Oxford, UK randomly immunized 696 infants with three types of needles:

  • Wide-long (23 gauge, 25 millimetre).
  • Narrow-short (25 gauge, 16 millimetre).
  • Narrow-long (25 gauge, 25 millimetre).

Parents recorded local and general reactions for three days after each dose, and antibody levels were measured after the third dose to look at the likely level of immune protection achieved.

"With increasing parental attention focused on the safety rather than the efficacy of vaccines, simple interventions that reduce local reactions, such as longer needles, should be welcomed," the researchers wrote.

"Vaccine manufacturers and national policymakers should consider needle size in recommendations for infant immunization."