Among the 62 NP swabs and 52 serum samples sent to Hawaii, 37 (60%) NP swabs and 42 (81%) serum samples were forwarded to CDC for further testing, including 1) measles virus genotype A (MeVA) real-time RT-PCR to detect measles vaccine virus; 2) measles and rubella serology, including IgM and IgG; 3) IgG avidity testing for measles and rubella; and 4) measles plaque reduction neutralization (PRN) to determine baseline immunity and differentiate recent infection from vaccination. Here, CD40LG is linked to rubella.