Prior infection by respiratory syncytial virus or parainfluenza viruses augments virus-specific IgG responses induced by the measles/mumps/rubella vaccine.

We found previously that immunizing cyclophosphamide-treated mice with one Paramyxoviridae virus mixed with dimethyl dioctadecyl ammonium bromide induces T cells which apparently also recognize other Paramyxoviridae viruses. This finding and the fact that respiratory syncytial virus (RSV) and parainfluenza viruses (PIVs) infect children early in life led us to ask if prior RSV or PIV infections influence the antibody response to measles and mumps vaccine viruses. Detection of virus-specific IgG in serum specimens collected randomly or at defined times after measles/mumps/rubella (MMR) vaccination was done with solid-phase enzyme immunoassays. The antibody-binding data obtained were converted to serum antibody titers by an immunoassay curve-fitting computer program. Prior infection by RSV and PIVs correlated with an augmented IgG response not only to measles and mumps virus, but also to rubella virus. Furthermore, the augmentation was greater for responders below the median response. These data show that common early childhood viral infections can influence immunity induced by the MMR vaccine.