A nurse is monitoring a 6-month-old infant 20 min after administering a hepatitis B immunization. Which of the following findings is the nurse's priority?

Choice A reason: A temperature of 37.7° C (99.9° F) is slightly elevated but not a cause for immediate concern after immunization. It can be a normal response. Choice B reason: Redness at the injection site is a common and expected reaction after immunization. It does not require immediate intervention. Choice C reason: Prolonged crying can occur after immunization, but it is not a priority over a potential allergic reaction indicated by hives. Choice D reason: Hives on the child's neck indicate a potential allergic reaction to the immunization. This is a priority finding and requires immediate attention from the nurse.