Would the MMR have made my son sleepy?

He had the MMR and the pneumonia jabs yesterday. Lots of momentary crying but not so much as a raised temperature since, which is good. However today he's had 3 naps! Which is unheard of for him. Usually I get a maximum of 20 minutes nap time from him in the day, but today he's clocked up at least 4 or 5 hours, and we didn't have a particularly early start. Would it be the jabs or just a coincidence?