Fig 1.
(A) Phylogenetic analysis of NAs originating from different A/H1N1 viruses isolated from human and swine (AA 1–469). Phylogenetic analysis of amino acid sequences of NAs originating from different A/H1N1 viruses isolated from human and swine (AA 1–469). The sequences were obtained from The NCBI Influenza Virus Sequence Database. Numbers of bootstrapping trees next to each node represent a measure of support for the node. (B) Three-dimensional model of the NA “head” (AA 83–469) was created using Cn3D software. Seven amino acid substitutions that differ in the NA head domain of A/California/07/09 (H1N1)pdm compared to A/South Africa/3626/13 (H1N1)pdm are shown in purple. (C) NA enzyme kinetics of A/California/07/09 (H1N1)pdm and A/South Africa/3626/13 (H1N1)pdm viruses. Substrate conversion velocity (Vi) of NA was measured as a function of substrate concentration.
Table 1.
Enzymatic properties of A/H1N1pdm09 NAs.
Fig 2.
The levels of “herd” immunity against A/California/07/09 (H1N1)pdm virus in 2009–2010 and 2015–2016 epidemic seasons among participants 20–59 years old.
*, P = 0.047.
Fig 3.
The antibody levels against A/H1N1pdm09 viruses in 134 blood donors 24–84 years of age examined in 2016.
(A) HI antibody titers against A/H1N1pdm09 viruses among participants with registered ILI or without ILI. GMT were calculated and used to represent the mean antibody levels. (B) Proportion of subjects with HI and NI antibody titers against surface antigens originated from A/South Africa/3626/2013 (H1N1)pdm or A/California07/2009 (H1N1)pdm strains; *, proportion of subjects with NI antibody titers ≥ 1:40 against A/South Africa/3626/13 (H1N1)pdm and A/California/07/09 (H1N1)pdm differ significantly (P < 0.0001). (C) Correlation analysis of NI antibodies against A/California/07/09 (H1N1)pdm versus A/South Africa/3626/13 (H1N1)pdm among blood donors. (D) Correlation analysis of NI antibodies against A/California/07/09 (H1N1)pdm versus A/South Africa/3626/13 (H1N1)pdm among patients seropositive to A/H1N1pdm viruses.
Fig 4.
Analysis of the sera from 48 participants negative to HA of A/H1N1pdm09 viruses, but positive to A/New Caledonia/20/99 (H1N1) or A/Puerto Rico/8/34 (H1N1).
(A) NI antibody levels against A(H1N1)pdm09 viruses. (B) Distance matrix of the A/H1N1 influenza viruses HA amino-acid sequences. Matrix shows identity between influenza virus strains.
Table 2.
Antibodies against HA and NA of A/H1N1 viruses among 134 subjects of different ages examined in 2016.
Fig 5.
The antibody levels against A/H1N1pdm09 viruses in paired sera from the A/H1N1pdm09-infected patients (n = 15).
(A) Increase in antibody titers against A/California/07/2009 (H1N1)pdm as determined by HI and NI assays and against A/South Africa/3626/2013 (H1N1)pdm as determined by HI and, NI, and MN assays. The antibody titers were expressed as log2. (B) Correlation between MN and HI antibodies against A/South Africa/3626/13 (H1N1)pdm in sera collected from the convalescents. (C) Correlation between MN and NI antibodies against A/South Africa/3626/13 (H1N1)pdm in sera collected from the convalescents. (D) Correlation between MN antibodies against A/South Africa/3626/13 (H1N1)pdm and HI antibodies against A/California/07/2009 (H1N1)pdm in sera collected from the convalescents. (E) Correlation between MN antibodies against A/South Africa/3626/13 (H1N1)pdm and NI antibodies against A/California/07/2009 (H1N1)pdm in sera collected from the convalescents. The “r” means Spearman’s rank correlation coefficient.