I don't know if this is the one that has been mentioned in connection with ME/"CFS," but, in, 1969, a mass vaccination program was undertaken in US schools using a new vaccine made from a live attenuated rubella virus (this was the first German Measles vaccine ever developed). The program was a preemptive attempt to thwart the expected, cyclic return of rubella by the winter of 1970. The main concern was that children would spread the disease to pregnant women. 20,000 birth defects had been attributed to the last US rubella outbreak in 1964.
I was 9 years old at the time and I don't think you could opt out of the vaccination program. I think this was also the first time that jet injector guns were used in a mass vaccination program in the U.S. They were certainly used at my grade school, where
everyone was lined up to get the injection.
Subsequent concerns were raised that the jet injector guns could become contaminated with biological material flung back at them from the patient's own arm as a result of the injection process. This created the possibility of cross-contamination between recipients with other agents, like Hepatitis B. The W.H.O. no longer recommends the use of jet injectors for this reason.
Whether any of this is connected to ME/"CFS," I don't know - but something else would have to be at work since I believe the vast majority of school age children in the US were vaccinated for rubella between 1969 and 1970.
http://en.wikipedia.org/wiki/Rubella
http://en.wikipedia.org/wiki/Jet_injector