Flu nasal spray offers similar protection against flu compared to standard flu shot
Intranasal live attenuated influenza vaccine was compared with inactivated influenza vaccine in children in rural, isolated communities in Canada.
Immunizing children with intranasal live attenuated influenza vaccine (LAIV) provides similar community protection against influenza to inactivated influenza vaccine (IIV), concluded a study of rural, isolated communities in Canada.
Most comparative flu vaccine studies assess direct protection only, so researchers conducted a cluster randomized trial in 52 Hutterite colonies in Alberta and Saskatchewan, Canada. Hutterite communities live lifestyles similar to Amish communities and are relatively isolated from cities and towns.
Researchers randomly assigned 1,186 children to receive the nasal spray vaccine and 3,425 children to receive the standard flu shot in a cluster randomized blinded trial conducted between October 2012 and May 2015, over 3 influenza seasons. Children were 36 months to 15 years (ages when they attend school; after this, Hutterite children are considered to have reached maturity).
The researchers administered standard dosing of either trivalent LAIV or trivalent IIV and looked at a primary outcome of reverse transcriptase polymerase chain reaction–confirmed influenza A or B virus in all participants (vaccinated children and persons who did not receive the study vaccine). Results were published by Annals of Internal Medicine on Aug. 16.
The nasal spray vaccine was very similar to the standard flu shot in providing direct protection to children and also in creating herd immunity, the researchers reported. Mean vaccine coverage among children in the LAIV group was 76.9% versus 72.3% in the IIV group. Influenza virus infection occurred at a rate of 5.3% (295 of 5,560 person-years) in the LAIV group versus 5.2% (304 of 5,810 person-years) in the IIV group. The hazard ratio (HR) comparing LAIV with IIV for influenza A or B virus was 1.03 (95% CI, 0.85 to 1.24).
For the secondary outcomes, there was no significant difference between vaccines in rates of reverse transcriptase polymerase chain reaction–confirmed influenza A (HR, 1.01; 95% CI, 0.59 to 1.74) or B (HR, 1.02; 95% CI, 0.76 to 1.35) virus in all participants. There was no significant difference in influenza A or B virus among all vaccinated children (HR, 0.97; 95% CI, 0.71 to 1.34). Among children vaccinated with LAIV, there was a significantly higher risk for influenza A virus infection (HR, 1.62; 95% CI, 1.02 to 2.59) but they were protected against influenza B virus (HR, 0.66; 95% CI, 0.46 to 0.96).
For indirect benefit, the HR in those who did not receive the study vaccine was 1.03 (95% CI, 0.85 to 1.24) for influenza A and B viruses. No difference was noted for influenza A (HR, 0.95; 95% CI, 0.79 to 1.15) or B (HR, 1.27; 95% CI, 0.88 to 1.84) virus.
The study authors pointed out that the study did not show superiority of the live vaccine but rather indicated that both vaccines had a similar effect. Recent observational studies showed that the nasal spray vaccine was ineffective, which prompted the CDC's Advisory Committee on Immunization Practices to recommend that the nasal spray not be used during the 2016-2017 flu season.
The authors wrote, “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, although we did not formally assess this.”