Recombinant IAV H3N2 (A/Aichi/2/1968) Nucleoprotein [His]

Introduction Since the influenza A/H1N1 pandemic of 2009 to 2010, numerous studies have described the clinical course and outcome of the different subtypes of influenza (A/H1N1, A/H3N2, and B). A recent systematic literature review concluded that there were no appreciable differences in either clinical presentation or disease severity among these subtypes, but study parameters limit the applicability of these results to military populations. We sought to evaluate differences in disease severity among influenza subtypes in a cohort of healthy, primarily outpatient adult U.S. Department of Defense beneficiaries. Materials and Methods From 2009 to 2014, we enrolled otherwise healthy adults age 18 to 65 years with influenza-like illness in an observational cohort study based in 5 U.S. military medical centers. Serial nasopharyngeal swabs were collected for determination of etiology and viral shedding by polymerase chain reaction. The presence and severity of symptoms was assessed by interview and patient diary. Results Over a 5-year period, a total of 157 adults with laboratory-confirmed influenza and influenza subtype were enrolled. Of these, 69 (44%) were positive for influenza A(H1N1), 69 (44%) for influenza A(H3N2), and 19 (12%) for influenza B. About 61% were male, 64% were active duty military personnel, and 72% had received influenza vaccine in the past 8 months. Almost 10% were hospitalized with influenza. Seasonal influenza virus distribution among enrollees mirrored that of nationwide trends each year of study. Individuals with A/H1N1 had upper respiratory composite scores that were lower than those with A/H3N2. Multivariate models indicated that individuals with A(H1N1) and B had increased lower respiratory symptom scores when compared to influenza A(H3N2) (A[H1N1]: 1.51 [95% CI 0.47, 2.55]; B: 1.46 [95% CI 0.09, 2.83]), whereas no other differences in symptom severity scores among influenza A(H1N1), influenza A(H3N2), and influenza B infection were observed. Overall, influenza season (maximum in 2012-2013 season) and female sex of the participant were found to be associated with increased influenza symptom severity. Conclusions Our study of influenza in a cohort of otherwise healthy, outpatient adult Department of Defense beneficiaries over 5 influenza seasons revealed few differences between influenza A(H1N1), influenza A(H3N2), and influenza B infection with respect to self-reported disease severity or clinical outcomes. This study highlights the importance of routine, active, and laboratory-based surveillance to monitor ongoing trends and severity of influenza in various populations to inform prevention measures.

Purpose: When influenza viruses are cultured in eggs, amino acid mutations of the hemagglutinin may occur through egg adaptation. On the other hand, when influenza viruses are cultured in animal cells, no antigenic mutation occurs unlike in eggs. Therefore, we examined whether the antigenic mutations actually occurred after passage of H3N2 (A/Texas/50/2012) virus up to 15 times in eggs and MDCK-Sky3851 cells. Materials and Methods: Prototype A/Texas/50/2012 (H3N2) influenza virus which was isolated from clinical patient, not passaged in egg, was obtained and propagated using the specific pathogen free egg and the MDCK-Sky3851 cell line up to 15 passage, and the changes in the antigen sequence of the influenza viruses were confirmed by gene sequencing and protein structure analysis. Results: In term of the hemagglutination titer of influenza virus, the reactivity to chicken and guinea pig red blood cell showed different results between egg propagated and cell propagated viruses. In the sequence analysis results for hemagglutinin and neuraminidase, no antigenic mutation was observed throughout all passages when cultured in MDCK-Sky3851 cells. On the other hand, mutations occurred in three amino acid sequences (H156R, G186S, S219F) in hemagglutinin up to 15 passages when cultured in eggs. Conclusion: H3N2 influenza virus cultured in eggs could lead mutations in amino acid sequence of hemagglutinin, distinct from the corresponding virus cultured in cells for which no antigenic mutation was observed. These findings suggest that cell culture is a more stable and effective way of production with lower risk of antigenic mutations for the manufacture of influenza vaccines.