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Resistance to influenza antiviral drugs
Neuraminidase inhibitors
H1N1 viruses that were resistant to the neuraminidase inhibitor oseltamivir were predominant in most regions of the world. Resistance was associated with the H275Y mutation in the neuraminidase gene within the A/Brisbane/59/2007 clade. All recent A/Hong Kong/2652/2006 clade viruses were sensitive to oseltamivir. There were no reports of oseltamivir resistant A(H3N2) or В viruses. No zanamivir resistant viruses were reported. Updates are available at
http://www.who.int/csr/disease/influenza/h1n1_table/en/index.html.
M2 inhibitors
Most influenza A(H3N2) viruses were resistant to amantadine and rimantadine. The majority of A(H1N1) viruses of the A/Hong Kong/2652/2006 clade were resistant, whereas those of the A/Brisbane/59/2007 clade were sensitive. Resistance in both subtypes was still predominantly associated with a serine to asparagine change in residue 31 of the M2 ion channel protein.
Studies with inactivated influenza virus vaccines
The presence of antibodies to the haemagglutinin (HA) of recent virus isolates was determined by HI tests in panels of sera from paediatric. adult and elderly subjects who had received trivalent inactivated vaccines. The following panels were used: tltree panels from adult, three from elderly and two from paediatric subjects, who had received vaccines containing the antigens of A/Brisbane/59/2007 (H1N1), A/Uruguay/716/2007 (H3N2) and B/Florida/4/2006; and one panel each from adult and elderly subjects who had received vaccines containing the antigens of A/Solomon Islands/3/2006 (H1N1), A/Brisbane/10/2007 (H3N2) and B/Brisbane/3/2007. The last two panels were only used for the analysis of influenza A(H3N2) and В viruses because the A(H1N1) component of this vaccine was obsolete at the time of analysis. Although HI tests were somewhat variable between laboratories the following conclusions could be made.
Vaccines containing influenza A/Brisbane/59/2007 (H1N1) antigen stimulated anti HA antibodies with geometric mean HI titles that were somewhat lower to recent isolates than to the vaccine virus (average reductions: children 51 %; adults 56 %; elderly 42 %).
Vaccines containing influenza A/Brisbane/10/2007 (H3N2)-like antigens stimulated anti HA antibodies with similar geometric mean HI titres to the vaccine virus and recent isolates. On a subset of sera, these HI results were supported by results from microneutralization tests.
Vaccines containing influenza B/Florida/4/2006-like antigens stimulated anti HA antibodies with similar geometric mean HI titres to the vaccine vims and recent B/Yamagata/16/88 lineage isolates. However, geometric mean HI titres were lower to recent B/Victoria/2/87 lineage isolates than to the vaccine virus (average reductions: children 35%; adults 67 %; elderly 56 %).
Recommended composition of influenza virus vaccines for use in the 2009-2010 influenza season
During the period September 2008 to January 2009, influenza A(H1N1), A(H3N2) and В viruses circulated in many parts of the world.
Outbreaks caused by influenza A(H1N1) viruses were reported in several countries. The majority of recent isolates were antigenically similar to the vaccine virus A/Brisbane/59/2007. Current vaccines containing A/Вrisbane/59/2007 antigens stimulated anti HA antibodies which were somewhat lower in title to recent isolates than to the vaccine virus.