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Media Myth On
Seasonal H3N2 Vaccine Utility Against trH3N2
The above comment on the cross reactivity between the current seasonal H3N2 vaccine, which targets A/Perth/16/2009, and the novel trH3N2 spreading across the country ignores the recent WHO data in its recent update on pandemic vaccines.
The report noted that production of a vaccine against A/Minnesota/11/2010 had started, and various activities were released in table 7, Antigenic properties of a recent A(H3N2 SOIV). The A/Perth/ 16/2009 (Perth/09) anti-sera had a titer of 640 against A/Perth/16/2009, but the level dropped to 10 for A/Indiana/08/2011, the first novel trH3N2 isolated.
All seven 2011 trH3N2 sequences are closely related to each other (and the sequences from the three Iowa cases are expected to be similar), and titer will be similar.
A titer of 10 is not protective and the current seasonal H3N2 vaccine will be of little value. Moreover, the cases in Indiana and Pennsylvania (as noted in MMWR early release on first two trH3N2 cases in 2011) had been vaccinated previously with the current tri-valent vaccine.
The H3 and N2 in trH3N2 is linked to seasonal H3N2 infection of swine in the early 1990’s, but the trH3N2 has evolved significantly from the H3N2 circulating in the 1990’s (as seen in phylogenetic trees in CDC report to FDA vaccine advisory committee), and as seen by the WHO data, the current seasonal vaccine will have little utility for the trH3N2 spreading throughout the United States.