A study in Gambian children who received the nasal spray flu vaccine before and after a 2009 H1N1 strain change suggests higher levels of vaccine virus shedding and immunogenicity for the 2009 H1N1 component of the updated version.
The authors say the lower shedding and immune response seen with the earlier version may help explain a reduced efficacy problem seen in other parts of the world with a different nasal spray flu vaccine that also underwent a similar strain change.
Researchers from Gambia, the United Kingdom, and the Netherlands reported their findings in the Jun 21 early online edition of The Lancet Respiratory Medicine. Though the flu burden is high in African children, few trials of live-attenuated influenza vaccine (LAIV) efficacy have been conducted in African children.
Vaccine updated for 2017-18 season
The LAIV studied in Gambia is Nasovac-S, a Russian-backbone flu vaccine made by Serum Institute of India. For comparison, FluMist—made by MedImmune and used in the United States and other countries—uses an Ann Arbor LAIV backbone. A 2013 study in Senegal found low efficacy for Nasovac-S, and around the same time, reduced effectiveness was found for FluMist in the United States.
For the 2017-18 season, the 2009 H1N1 vaccine virus component was updated in both vaccines, and the authors note that no studies have been published that shed light on whether the change affected shedding and immunogenicity of that LAIV component.
For the Gambian phase 4 study, 118 children ages 24 to 59 months received one dose of LAIV that contained the earlier 2009 H1N1 virus component from 2016 to 2017. The team also studies a separate cohort of 135 children who received one dose of the LAIV containing the new 2009 H1N1 component from 2017-18. The researchers examined LAIV strain shedding at day 2 and day 7, hemagglutinin inhibition seroconversion, and an increase in hemagglutinin-specific IgA and T-cell responses 21 days after LAIV administration.
They found that shedding and immunogenicity for the earlier 2009 H1N1 strain, A/California/2009/38, was less than for the H3N2 and influenza B components, which they said may explain the lack of efficacy seen in the Senegal trial. They also found a significant increase in virus shedding, improved seroconversion, and improved T-cell responses after the vaccine virus switch.
Effectiveness not yet shown
In an accompanying commentary, two infection disease specialists wrote that the study fills an important gap by providing the first published immunogenicity data for LAIV in Africa. The authors are Cheryl Cohen, PhD, with South Africa's National Institute for Communicable Diseases and the University of Witwatersrand, and Sheena Sullivan, PhD, MPH, with the World Health Organization (WHO) Collaborating Centre in Australia.
Though the findings suggest that updating the vaccine component improved immune response and is consistent with findings for FluMist, Cohen and Sullivan say it's still not clear if the improvements correspond with improved effectiveness.
Jun 21 Lancet Respir Med abstract
Jun 21 Lancet Respir Med commentary