CD40LG and infection: Although IgM levels were similar and below the positivity threshold in saliva (Fig. 4a), significantly higher IgM levels, albeit still below the positivity threshold, were observed in serum in previously infected individuals than in infection-naive individuals at 2 and 6 months after first vaccination (P = 0.0056 and P = 0.0039, respectively) (Fig. 4b).