Effect of neonatal circumcision on pain responses during vaccination in boys
Study published in The Lancet, Volume 345, Number 8945: Pages 291-292, 4 February 1995. doi:10.1016/S0140-6736(95)90278-3
The study notes, "Circumcised babies have short-term alterations in behaviour, sleep patterns, frequency of feeding, crying, fussiness, and heart rate." For the longer term, the study notes,
Male circumcision . . . causes intense pain and measurable changes in behaviour that last up to 1 day. We found that circumcision status was associated with increased infant pain response to routine vaccination at 4-6 months. Circumcised boys had significantly longer crying bouts and higher pain scores. That both outcome measures, pain index, and cry duration, were influenced by circumcision lends credibility to our observations.
The full text is available on The Lancet site and at the CIRP library.