Intranasal live attenuated flu vaccine offers similar protection as inactivated flu vaccine
Immunizing children with the intranasal live attenuated influenza vaccine (LAIV) provides similar protection against influenza than the inactivated influenza vaccine (IIV or standard flu shots), contrary to previous belief that LAIV is superior to IIV, a recent study reveals.
“Our results are important because in previous years [and as late as June 2014], the live vaccine had first been preferred for children... Then, subsequently, it was no longer preferred and now not recommended at all,” said lead author Professor Mark Loeb of the Department of Pathology and Molecular Medicine at McMaster University in Ontario, Canada.
“Our study challenges previous studies because our results show conclusively that the vaccines show similar protection when both direct and indirect effects are taken into account.”
The cluster, double-blind clinical trial randomized 1,186 children and adolescents aged 3–15 years (young people) to standard dosing of LAIV or IIV. The participants were from the Hutterite colonies, where members live communally in areas relatively isolated from towns and cities.
Similar proportion of young people received vaccination in both LAIV and IIV groups (76.7 percent vs 72.4 percent), and both groups had similar rates of influenza infection (5.3 percent vs 5.2 percent).
There was no significant difference in the risk of influenza A or B virus infection between LAIV- or IIV-vaccinated young people (hazard ratio [HR], 0.97, 95 percent confidence interval [CI], 0.71–1.34).
When stratified by age, children younger than 6 years who were vaccinated with LAIV or IIV had similar influenza infection rates (6.9 percent vs 6.2 percent) as those in the older children (6.3 percent vs 6.4 percent).
When including 3,425 nonvaccinated members in the analysis, influenza infection rate in the LAIV group was also not significantly different than the IIV group (pooled HR, 1.03, 95 percent CI, 0.85–1.24), reflecting the indirect benefit of vaccination for members who were not vaccinated in the study.
Additionally, no significant difference was found in clinically relevant outcomes between both groups, including visits to physicians for respiratory illness (0 percent, 95 percent CI, -0.82 to 0.81), emergency department visits (-0.10 percent, 95 percent CI, -0.57 to 0.37), and absence from school or work (0.22 percent, 95 percent CI, -0.92 to 1.36).
More children in the IIV group had vaccine-related adverse reactions than the LAIV group, which the researchers attributed to reactions at the injection site. However, none of these were serious events.
“Given the similar effect of LAIV and IIV on laboratory-confirmed influenza and secondary outcomes in our study, inactivated vaccines that are available at a lower cost seem to be cost-effective,” said the researchers, although this has not been not formally assessed in the study, they noted.