A second systematic Review reports first measles vaccines (MV) administered to infants < 9 months age, followed by additional doses at later ages, results in high seropositivity and effectiveness but may result in lower titres after 1 or 2 subsequent doses vs a MV schedule starting at older age.
A related commentary which discusses the findings from both systematic reviews suggests that MV administration before 9 months of age must only be considered as an emergency solution to contain or prevent outbreaks and cannot replace either scheduled dose. Compared with infants administered MV at 9 months of age or later, seroconversion and antibody concentrations in those vaccinated before 9 months of age were significantly reduced. Vaccine efficacy was 51% versus 83%, highlighting that a substantial proportion of infants younger than 9 months remained susceptible to measles, and that only further doses could ensure that all infants were protected.
Furthermore, these results suggests that an early dose might decrease long-term protection because further doses were associated with reduced antibody titres and avidity.
The commentary concludes that suboptimal vaccination coverage reported recently in the EU and US can only be solved with total compliance to MV recommendations.