|
| ||||||||
| ||||||||
|
Biosecurity BriefingFlu Season Marked by Vaccine Mismatch, Antiviral Resistance in Europe By Eric Toner, February 15, 2008 According to a recent report from the U.S. Centers for Disease Control and Prevention (CDC), this year’s seasonal influenza epidemic is more severe than those of the last two years. The CDC also reports that there is a mismatch between this year’s vaccine and two of the predominant circulating strains of flu virus;1 at the same time, European health authorities are reporting an unexpected, and so far unexplained, emergence of H1N1 virus with a mutation associated with decreased sensitivity to oseltamivir.2,3 CDC data from the week ending February 2 indicate that 48 of 51 jurisdictions (all 50 states plus the District of Columbia) are reporting regional or widespread flu outbreaks. A sudden jump in mortality attributed to pneumonia and flu, along with increased physician visits for influenza-like illness during the two weeks prior (January 20-February 2), indicate that this season is more severe than the previous two.1 The CDC also reports that, as was the case last year, antigenic typing of flu isolates shows that A/H1N1 is the predominant strain nationally (see Table 1, below). However, both influenza A/H3N2 and influenza B are increasing in frequency and are now predominant in some regions. In the Mid-Atlantic region, half of the isolates have been influenza B during the last 4 weeks, while in the North Central region, H3N2 has been the most frequent isolate. To date, 87% of this year’s H3N2 isolates are the Brisbane strain, which was not included in this year’s vaccine, and 93% of the influenza B virus isolates belong to the Yamagata lineage, also not included in this year’s vaccine.1 Consequently, this year’s vaccine currently does not match 43% of flu isolates in this country.
The degree of cross-protection afforded by this year’s vaccine against these strains is uncertain. Scientific evidence suggests that some degree of cross-protection is possible due to the fact that H3N2/Brisbane is a recent variant that evolved from H3N2/Wisconsin, a strain that is included in the current vaccine.4 However, it is thought that there is less likely to be cross-protection between the B/Yamagata strain and the B/Victoria vaccine strain.5 On a related note, reports from Europe indicate that 20% (151/755) of this year’s H1N1 isolates contain a genetic mutation that has been associated with decreased sensitivity to the antiviral drug oseltamivir.2,3 In Europe, 80% of the isolates are influenza A, and 98% of those are H1N1. Oseltamivir is not commonly used in Europe to treat seasonal influenza.4 The World Health Organization (WHO) reports that evidence of oseltamivir resistance has been found in H1N1 viruses isolated from 18 of 37 countries.6 In Norway and in France, 63% and 39% of H1N1 viruses isolated, respectively, have shown genetic mutations associated with oseltamivir resistance. None of the patients in Norway from whom resistant viruses were isolated had been treated, or had known contact with anyone who had been treated, with oseltamivir.7 In contrast, the CDC reported that 8% of H1N1 isolates from the United States have the mutation that has been associated with oseltamivir resistance (4.5 % of all influenza viruses tested). As reported on February 14, 2008 by CIDRAP News, in light of new surveillance data, WHO announced that all three components of next year’s flu vaccine for the northern hemisphere should be changed. In addition to CDC’s announcement regarding the mismatch between the influenza A/H3N2 and influenza B components of this year's vaccine, WHO reports “that the majority of recent H1N1 virus isolates globally have not matched well with the H1N1 component of the vaccine.” Although it is not unusual for one or two components of the vaccine to be changed, “replacing all three is less common.”6 References
| ||||||||||||||||||||||||||||||