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Volume 26, Number 9—September 2020

Detection of H1 Swine Influenza A Virus Antibodies in Human Serum Samples by Age Group1

Elien Vandoorn, Isabel Leroux-Roels, Geert Leroux-Roels, Anna Parys, Amy Vincent, and Kristien Van ReethComments to Author 
Author affiliations: Ghent University, Merelbeke, Belgium (E. Vandoorn, A. Parys, K. Van Reeth); Ghent University and Ghent University Hospital, Ghent, Belgium (I. Leroux-Roels, G. Leroux-Roels); National Animal Disease Center, Ames, Iowa, USA (A. Vincent)

Main Article

Table 2

Percentage amino acid homology (lower left) and number of identical amino acids out of 50 aa in presumed antigenic sites (upper right) (28) between hemagglutinin 1 of human and swine H1 influenza A viruses used as test viruses in hemagglutination inhibition and virus neutralization assays*

Virus strain
Eurasian avian

Human seasonal

Classical swine
Europe 1C.2.1
Asia 1C.2.3
Europe 1B.1.2.1
N. Am. 1B.2.2.1
N. Am. 1B.2.2.2
N. Am. 1B.2.2.2
N. Am. 1A.3.3.3
World 1A.3.3.2
swG10 49 22 19 23 24 23 23 23 32 34


TW86 73.4 72.2 41 41 38 36 32 38 23 23



NC99 73.3 72.1 93.9 85.9 42 42 36 47 24 24
swAL16 71.5 71.2 89.3 81.6 91.4 45 40 40 23 27
swIL10 72.1 71.5 89.6 83.4 94.2 92.9 43 42 23 25





swOH07 74.0 74.3 74.3 71.6 73.0 72.4 71.8 70.5 73.6 44
CA09 73.4 72.5 73.4 70.9 72.4 73.9 72.1 71.1 72.4 90.8

*Viruses are ordered chronologically according to the year of circulation of the selected human test viruses TW86, NC99, BR07, and CA09; horizontal rules within table represent grouping of epidemiologically related human and swine influenza A viruses, with the oldest (ancestor) virus mentioned first. Complete isolate names are provided in Table 1. IAV, influenza A virus; N. Am., North America; –, not applicable.
†Human IAV that no longer circulates; TW86 is the presumed human precursor for human-like H1 swine IAVs in Europe; NC99 is the presumed human precursor for human-like H1 swine IAVs in North America; BR07 is a human seasonal IAV that circulated right before the influenza A(H1N1)pdm09 virus; the influenza A(H1N1)pdm09 virus, represented by CA09, is circulating in both humans and swine worldwide.

Main Article

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1Preliminary results from this study were presented at the Fourth International Symposium on Neglected Influenza Viruses, April 18–20, 2018, Brighton, United Kingdom; at the BELVIR conference, December 20, 2018, Brussels, Belgium; and at the 1918 Pandemic Conference, February 7–8, 2019, Ypres, Belgium.

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