LAIV ineffective in 2013-2014 flu season
Data from the U.S. Flu Vaccine Effectiveness Network showed that quadrivalent live-attenuated influenza vaccine offered little protection to children during the 2013-2014 flu season.
“It is important that we continue to improve influenza vaccination coverage in children to reduce the overall illness burden of influenza, both by direct and indirect protection,” Manjusha Gaglani, MD, a pediatric infectious disease specialist at Baylor Scott & White Health, told Infectious Disease News. "Children aged 6 to 23 months can receive the inactivated flu shot and children aged 2 years or older can receive either the live or the inactivated vaccine, based on their individual health condition.”
In June 2014, the Advisory Committee on Immunization Practices (ACIP) recommended the live-attenuated influenza vaccine (LAIV) over inactivated influenza vaccine (IIV) in healthy children aged 2 to 8 years who have no contraindications or precautions. That recommendation was withdrawn in 2015 due to conflicting data.
In a report published in The Journal of Infectious Diseases, Gaglani and colleagues used test-negative case-control data from the U.S. Flu VE Network to compare the effectiveness of LAIV and IIV during the 2013-2014 season, when A(H1N1)pdm09 was the predominant strain. The analysis included 5,637 vaccine recipients.
An ‘unanticipated finding’
Results of the analysis indicated that during the 2013-2014 season, overall vaccine effectiveness against A(H1N1)pdm09-related illness was 54% (95% CI, 46%-61%), which was consistent with estimates reported since 2009.
“Since there has been minimal antigenic drift in A(H1N1)pdm09 viruses and the vaccine H1N1 component A/California/7/2009 has remained unchanged since 2009, these results were not unexpected,” Gaglani and colleagues wrote.
However, the effectiveness of quadrivalent LAIV among fully vaccinated children aged 2 to 17 years was only 17% (95% CI, –39% to 51%) vs. 60% (95% CI, 36%-74%) with IIV — the only vaccine of the two that offered “significant protection” against A(H1N1)pdm09 that season, according to the researchers.
Gaglani and colleagues said one possible explanation for the “unanticipated finding” of the poor performance of LAIV is that the A(H1N1)pdm09 construct is less stable in higher ambient temperatures than other viruses included in the vaccine. Environmental stressors, like a break in the cold chain, for example, could potentially diminish its efficacy.
“Selection of an A(H1N1)pdm09 virus with improved thermostability for LAIV may improve the consistency of results but will require evaluation of effectiveness during another season when A(H1N1)pdm09 viruses circulate,” the researchers wrote.
Results also suggested A(H1N1)pdm09-containing vaccines offered some residual protection among individuals aged at least 9 years and among children aged 2 to 8 years if they had been fully vaccinated the previous season, although individuals with current vaccinations were somewhat better protected against influenza.
The mystery of immunity
Eighty years have passed since Robert E. Shope, MD, isolated influenza virus, and the scientific community’s understanding of human immunity against the virus is still incomplete, according to Andrew T. Pavia, MD, chief of the division of pediatric infectious diseases at the University of Utah School of Medicine.
“Many have called for new influenza vaccines, but, in the meantime, careful studies will help us understand and better use existing vaccines,” he wrote in a related editorial. “The characteristics of an optimal vaccine might include rapid and inexpensive production, broad protection against drifted and pandemic strains, and production of T-cell and B-cell memory. This goal is unlikely to be achieved by novel vaccine constructs alone. It will require a deeper understanding of the enigmas and mysteries of influenza pathogenesis and immunity.” – by John Schoen
Disclosures: Gaglani reports receiving grants from the CDC during the conduct of the study and grants from MedImmune/AstraZeneca outside of the study. Please see the full study for a list of all other authors’ relevant financial disclosures. Pavia reports receiving grants from BioFire Diagnostics, personal fees and other compensation from Antimicrobial Therapy, and personal fees from WebMD.