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Correlates of Protection after Vaccination Immune correlates of protection against influenza infection after vaccination include serum hemagglutination inhibition antibody and neutralization antibody (15,92). Increased levels of antibody induced by vaccination decrease the risk for illness caused by strains that are antigenically similar to those strains of the same type or subtype included in the vaccine (93-96). Although high titers of these antibodies correlate with protection from clinical infection, certain vaccinated persons with low levels of antibody after vaccination also are protected. The majority of healthy children and adults have high titers of antibody after vaccination (94,97). However, in certain studies, antibody levels in certain participants declined below levels considered protective during the year after vaccination, even when the current influenza vaccine contained one or more antigens administered in previous years (98,99). Other immunologic correlates of protection that might best indicate clinical protection after receipt of an intranasal vaccine such as LAIV (e.g., mucosal antibody) are more difficult to measure (91,100). |