In infants, pain from vaccinations shows up in brain activity

Infants show distinct, consistent patterns of brain activity in response to painful vaccinations, reports a study in the February issue of PAIN®, the official publication of the International Association for the Study of Pain. The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health.

"We have shown that inoculation evokes, from the time of the first needle contact, a clearly defined EEG response in infants up to at least one year of age," write Dr Madeleine Verriotis and colleagues of University College London. They believe this "brain-led approach" to assessing procedure-related pain in infants may help in developing improved vaccination techniques and pain-relieving treatments.

Brain Activity in Response to Shots in Infants...

The researchers performed elecroencephalography (EEG) in 15 healthy babies receiving routine vaccinations. A noninvasive and painless procedure, EEG is done to measure electrical activity in the brain, using electrodes placed in specific locations on the scalp. Twelve infants were tested during vaccinations at age one to two months, and five at age 12 months.

Dr Verriotis and colleagues compared the EEG findings with behavioral pain responses: facial expression, crying, and movements. Such behavioral responses are the standard method for assessing pain in preverbal infants. The researchers filmed the procedures to identify the precise timing of EEG responses to vaccination pain.

Sometimes the "ouch" of a vaccination doesn't end when the needle's out. Soreness or a low fever can sometimes appear afterwards, along with some fussiness.

What to Do About Side Effects

A warm compress applied after the shot can help reduce soreness, as can moving the arm or leg in which the shot was given (you can "bicycle" a baby's leg to help bring relief, or encourage a toddler to do a few rounds of head-shoulder-knees-and-toes). A non-aspirin pain reliever such as acetaminophen (after age three months) or ibuprofen (after age six months) can help with residual achiness, as well as with any low-grade fever, so ask the doctor about that before you leave the office. Some doctors even recommend a dose of a non-aspirin pain reliever before the shot is given, to prevent these mild side effects in the first place.

The EEG recordings showed two clear waveforms, or "spikes," which appeared within milliseconds after the first contact of the needle with the infant's skin. Although the waveforms appeared in both age groups, they were significantly larger in one- to two-month-old infants than in one-year-olds.

In three infants studied at both ages, the EEG responses - particularly for the first waveform - appeared clearer and larger at age 12 months. The EEG patterns were also more reproducible in older infants. The researchers suggest that these age-related differences might reflect developmental changes in the brain during the first year of life: an increased number of neurons (nerve cells), a larger proportion of neurons being activated, or better synchronization of firing activity.