Babies should be given something sugary before a jab to reduce pain, Canadian researchers say.
Experts at the University of Toronto say newborns are less likely to cry if given a few drops of a sugar solution before immunisation.
Data based on 1,000 injections suggests infants given a glucose solution are 20% less likely to cry following a jab.
The research, published in Archives of Disease in Childhood, is based on clinical data from 14 studies.
A team led by Dr Arne Ohlsson, of the University of Toronto, looked at data from clinical trials in babies up to a year old.
As well as the findings related to glucose, the researchers found that between a few drops and half a teaspoon of sucrose and glucose also led to a small reduction in the amount of time a baby spent crying.
The Canadian researchers, who worked in collaboration with colleagues in Australia and Brazil, concluded: "Healthcare professionals should consider using sucrose or glucose before and during immunisation."
Existing research points to the pain-relieving properties of sweet solutions working for babies undergoing painful procedures such as a heel prick.
Adam Finn, professor of paediatrics at the University of Bristol, said: "Anything we can do to minimise the discomfort of immunisation for children is to be welcomed, and I would like to see more research in this area.
"On the one hand parents are more likely to return if the experience is not distressing.
"But more fundamentally, children don't agree to have vaccines, so we need to be sure we are making it as painless as possible for them."