Antigenicity of the 2015–2016 seasonal H1N1 human influenza virus HA and NA proteins

Abstract

Antigenic drift of the hemagglutinin (HA) and neuraminidase (NA) influenza virus proteins contributes to reduced vaccine efficacy. To analyze antigenic drift in human seasonal H1N1 viruses derived from the 2009 pandemic H1N1 virus (pH1N1-like viruses) accounts for the limited effectiveness (around 40%) of vaccination against pH1N1-like viruses during the 2015–2016 season, nasal washes/swabs collected from adult subjects in the Rochester, NY area, were used to sequence and isolate the circulating viruses. The HA and NA proteins from viruses circulating during the 2015–2016 season encoded eighteen and fourteen amino acid differences, respectively, when compared to A/California/04/2009, a strain circulating at the origin of the 2009 pandemic. The circulating strains belonged to subclade 6B.1, defined by HA amino acid substitutions S101N, S179N, and I233T. Hemagglutination-inhibiting (HAI) and HA-specific neutralizing serum antibody (Ab) titers from around 50% of pH1N1-like virus-infected subjects and immune ferrets were 2–4 fold lower for the 2015–2016 circulating strains compared to the vaccine strain. In addition, using a luminex-based mPlex HA assay, the binding of human sera from subjects infected with pH1N1-like viruses to the HA proteins from circulating and vaccine strains was not identical, strongly suggesting antigenic differences in the HA protein. Additionally, NA inhibition (NAI) Ab titers in human sera from pH1N1-like virus-infected subjects increased after the infection and there were measurable antigenic differences between the NA protein of circulating strains and the vaccine strain using both ferret and human antisera. Despite having been vaccinated, infected subjects exhibited low HAI Ab titers against the vaccine and circulating strains. This suggests that poor responses to the H1N1 component of the vaccine as well as antigenic differences in the HA and NA proteins of currently circulating pH1N1-like viruses could be contributing to risk of infection even after vaccination.

Molecular characterization of the influenza A(H1N1)pdm09 isolates collected in the 2015‐2016 season and comparison of HA mutations detected in Turkey since 2009

“…Accordingly, the total number of amino acid mutations (14 common, 1 less common, and 11 rare) in the 2015‐2016 season was higher than of the previously reported by Guldemir et al The 90%‐100% of our isolates carried 14 common mutations (P83S, S84N, D97N, S162N, K163Q, S185T, S203T, I216T, A256T, K283E, I321V in HA1 and E47K, S124N, E172K in HA2). These mutations have been previously reported from different parts of the world in isolates of the same period . A less common S185P mutation was seen instead of S185T in 10% of our isolates, and we also identified rare mutations (C4S, T72A, I96V, N260D, I266F, L314M, S326F in HA1 and I45V, V66A, R106K, F140L in HA2) in individual isolates.…”

“…Antigenic site distribution of the common mutations detected by us was like those of other studies carried out in the same period: S162N and K163Q in Sa, S203T in Ca1, and S185T/P in Sb . Particularly, S185T/P located in antigenic site Sb was also residing within the 190‐helix domain of the receptor‐binding site, and the amino acid changes in or near the RBS domain of HA had previously been shown to influence the antigenic properties of influenza A(H1N1)pdm09 viruses .…”

“…Regarding the 2015‐2016 season, subclades 6B.1 and 6B.2 appeared as new clusters in clade 6B. In Turkey, all studied influenza A(H1N1)pdm09 isolates of this season belonged only to 6B.1 as detected in studies by Komissarov et al, Korsun et al, Clark et al, Puig‐Barberà et al, Mohebbi et al Cocirculation of 6B.1 and 6B.2 isolates was also observed in some other studies …”

“…Glycosylation of HA has been recognized as another factor affecting antigenicity and playing important role in the evolution of influenza A(H1N1)pdm09 viruses since variations of the carbohydrate site chains on HA have been shown to alter the antibody‐mediated neutralization of virus . Accordingly, S162N was suggested as a specific mutation due to a potential gain of new glycosylation site that may shield the Sa epitope for escaping the pre‐existing immunity . Further to these common mutations, a rare mutation detected in our study, T72A, was also residing in Cb.…”

“…The common HA mutations detected in Turkish isolates of the 2015‐2016 season have previously been identified by other groups, and the accessibility of residues associated with antigenic sites and their possible impact in the antigenicity of the protein has already been discussed in detail . Despite carrying a higher number of HA mutations compared to the progenitor virus, the new subclades 6B.1 and 6B.2 of the 2015‐2016 season were closely related to the vaccine virus A/California/7/2009 and found to be antigenically indistinguishable by postinfection ferret antisera.…”