In a study of MMR seropositive volunteers who received a booster shot (similar to our subject), low frequencies of virus-specific ASCs were found 1 week postvaccination; the median number of virus-specific ASCs per 106 PBMCs were just 0.38 for mumps, 0.125 for measles, and 2.25 for rubella (Latner et al. 2011). Here, MRC1 is linked to rubella.