Paradigm Shift Intervention Monitoring
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Commentary
H3N2 Low
Reactor With L157S
Recombinomics
Commentary 16:30
December 31, 2012
• 2 (1.3%) of the 155 H3N2 viruses tested showed reduced titers with antiserum produced against A/Victoria/361/2011.
• 279 (99.3%) of the 281 H3N2 influenza viruses tested have been characterized as A/Victoria/361/2011-like, the influenza A (H3N2) component of the 2012-2013 Northern Hemisphere influenza vaccine.
• 2 (0.7%) of the 281 H3N2 viruses tested showed reduced titers with antiserum produced against A/Victoria/361/2011.
The above FluView comments (in red) report the first two H3N2 low reactors in the 2012/2013 (in week 48), while the subsequent comments (in blue) from the current FluView (week 51) indicate these two low reactors represent 0.7% of the H3N2 isolates tested to date. Although these numbers suggest the current H3N2 vaccine target is a good match the the virus circulating in the United States, the recently released CDC sequences from the first 50 cases in the 2012/2013 season indicated the low reactors cited above are common.
Thirty-five of the 50 sequences (from collections were between October 1 and November 14) are the same sub-clade as the H3N2 target, A/Victoria/361/2011 (which was also true for 12 of the 14 November collections). The two sequences from the low reactors cited above were from Iowa, A/Iowa/14/2012, and Hawaii and mapped with the Victoria/361 sub-clade. However, each mapped on a separate branch and the reduced titers with the vaccine were due to two separate changes.
The Hawaii sequence, A/Hawaii/29/2012, had a limited number of HA changes, which included L157S, which is a region of HA that strongly affects antigenicity (changes at positions 157-160 frequently produce “low reactors” as was seen for Hawaii/29).
The early spread of H3N2 this season has raised concerns that the current flu season would mimic the 2003/2004 season due to the spread of A/Fujian/411/2002, which produced a dramatic spike the Pneumonia and Influenza death rate, which included a large number of children. The high number of adolescent deaths was followed by regulations which made adolescent influenza deaths reportable. In week 51, the CDC reported a large spike in adolescent deaths, which is an undercount of the number of confirmed cases reported by state labs.
The 2012/2013 US isolates with L157S are listed below.
US 2012/2013 Isolates With L157S
A/New Hampshire/12/2012 November 8
A/Massachusetts/07/2012 November 5
A/Hawaii/30/2012 October 17
A/New York/38/2012 October 17
A/Hawaii/29/2012 October 15
A/Hawaii/28/2012 October 1
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