BOSTON — Live-attenuated vaccines are more effective than trivalent inactivated vaccines in inducing mucosal antibody production, which better parallels with induction of protection against viral replication than the systemic response, according to preliminary data presented here at the 2012 Pediatric Academic Societies Annual Meeting.
To determine the components of protection of the immune response afforded to TIV or LAIV, researchers compared mucosal and systemic antibody responses to one dose of TIV or LAIV in children aged 2 to 9 years. A second dose of LAIV was then used to assess the suppression of viral replication by the prior administration of LAIV or TIV.
“We actually know more about the protection afforded by the LAIV in young children than we do about the TIV because in introducing that vaccine, which was more recent than the TIV, there were a number of clinical trials that indicated an efficacy of 90%,” Peter F. Wright, MD, professor of pediatrics at Dartmouth Medical School, told Infectious Diseases in Children. “Physicians use the two vaccines fairly interchangeably and tend not to differentiate between them, yet there are key differences.”
In this randomized study, vaccine viral shedding, as well as mucosal and serum antibody responses, were analyzed in 25 children enrolled for 2 years. Vaccination safety was assessed by parental monitoring of symptoms in the first 7 days after each vaccination. Nasal secretions and sera were analyzed for the presence of immunoglobulin A and IgG specific to influenza A H1N1 and H3N2, and influenza B before and after each vaccination.
Serum and nasal swab samples obtained on days 0, 28 and 56 were tested by kinetic enzyme-linked immunosorbent assay (ELISA) for presence of haemagglutination-specific immunoglobulins, as well as haemagglutination inhibition and infectivity neutralization assays. Nasal secretions were assessed for evidence of viral shedding after administration of LAIV on days 0, 2, 4 and 7 after each LAIV dose by quantitative reverse transcriptase-polymerase chain reaction, determination of TCID50 and plaque assays.
According to study results, LAIV successfully induced viral shedding. Researchers observed that the first dose of LAIV induced mucosal antibody response more effectively than TIV, which correlates with greater protection against shedding upon re-challenge with the second LAIV dose: TIV induced systemic strain-specific antibody response to 78% of strains, whereas LAIV induced antibody response to 44%.
“While both LAIV and TIV are effective vaccines against clinical illness in the vaccine recipient, LAIV appears to be much more effective at preventing virus-shedding on subsequent exposure.” Wright said. “One hypothesis that the LAIV in a community setting might be much more effective at preventing spread of virus, for example in a patient who might have received TIV, not succumb to sickness themselves, but still shed a considerable amount of virus.” — Robert Stott
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Disclosure: Dr. Ilyushina reports no relevant financial disclosures.