Antibody responses to natural influenza A/H1N1/09 disease or following immunization with adjuvanted vaccines, in immunocompetent and immunocompromised children

Abstract: Objectives: To compare antibody responses elicited by influenza A/H1N1/09 disease and immunization with adjuvanted vaccines, in immunocompetent or immunocompromised children. Study design: Prospective parallel cohort field study enrolling children with confirmed influenza A/H1N1/09 disease or immunized with 1 (immunocompetent) or 2 (immunocompromised) doses of influenza A/H1N1/09 squalene-based AS03- or MF59-adjuvanted vaccines. Antibody geometric mean titers (GMT) were measured by hemagglutination inhibition (HAI) and microneutralization (MN) assays 4–6 weeks after vaccination/disease. Vaccine adverse events were self-recorded in a 7-day diary. Results: Antibody titers were as high in 48 immunocompetent children after a single immunization (HAI and MN seroprotection rates: 98%; HAI-GMT: 395, MN-GMT: 370) as in 51 convalescent children (seroprotection rates: 98% (HAI) and 92% (MN); GMT: 350 (HAI) and 212 (MN). Twenty-seven immunocompromised children reached slightly lower seroprotection rates (HAI: 89%, MN: 85%) but similar antibody titers (HAI-GMT: 306, MN-GMT: 225) after 2 immunizations. Adverse events increased with age (P =0.01) and were more frequent with Pandemrix® than Focetria® (P =0.03). Conclusions: Similarly high seroresponses may be expected in immunocompetent children after a single dose of adjuvanted vaccines as responses of convalescent children. Two vaccine doses were sufficient for most immunocompromised children. Trial registration: NCT0102293 and NCT01022905. [Copyright &y& Elsevier]