# 1144
The International Society for Infectious Diseases (ISID) provides detailed reporting and analysis of emerging infectious diseases via daily email alerts called promed-mail. For those interested in such things, subscribing is free and easy to do.
Today Promed has released a review of worldwide influenza reporting for this past summer (May 20th - Sept 15th). The full report can be accessed here. The orginal source for this material is the CDC's Morbidity and Mortality Weekly Report.
While only a small number of the total cases of flu are sampled and identified each year, it is hoped that the results are reasonably representative of what is happening in the field. As you will see, this summer was a mixed bag, with no single flu stain taking the lead.
Even at this late date it is impossible to know which strain of flu will take off this winter, so you can imagine how difficult it must be for scientists to decide on what strains to include in each year's vaccine, which must be decided on six months in advance.
This year's vaccine will contain antigens for two Influenza A viruses (H1N1 & H3N2), and 1 Influenza B virus. The strain of H1N1 included is known as A/Solomon Islands/3/2006 while the H3N2 strain included is A/Wisconsin/67/2005. The B virus strain included comes from the B/Victoria/02/87 lineage.
It is a guessing game each Spring trying to decide, months in advance, which of the circulating flu viruses will dominate in the fall. Some years scientists hit it pretty close, other years they don't.
The good news is that of the very small sample of H1N1 viruses collected and analyzed this summer, all of them were antigenically similar to this year's vaccine component (A/Solomon Islands/3/2006).
It should be noted, however, that only 4 H1N1 samples were analyzed.
Less encouraging, are the results of the H3N2 sampling, as explained in this excerpt from the promed-mail report.
Of the 94 influenza A (H3) viruses that were characterized (4 from Europe, 78 from Latin America, 4 from Asia, 2 from Africa, and 6 from the United States), 17 (18 percent) were antigenically similar to A/Wisconsin/67/2005, the H3N2 component of the 2007-08 influenza vaccine, whereas 77 (82 percent) had reduced titers to A/Wisconsin/67/2005.
Basically, only 18 percent of the samples received were a good match with this year's vaccine. That means that if the H3N2 virus becomes the dominate strain this winter, this year's flu shots will likely be less effective than hoped.
The `B' Component of the vaccine may be problematic this year as well. There are currently two major strains of B Influenza circulating in the world, the B/Victoria and the B/Yamagata lines. This year, the decision was made to include the B/Victoria lineage in the vaccine.
This, again, from Promed-Mail.
Of the eight influenza B isolates collected during 20 May-8 Sep 2007 and characterized at CDC, one belonged to the B/Victoria lineage (from Asia). This B/Victoria-lineage virus was similar to B/Ohio/01/2005; B/Ohio/01/2005 is antigenically equivalent to B/Malaysia/2506/2004, the recommended influenza B component for the 2007-08 influenza vaccine. The remaining 7 influenza B viruses (3 from South America, 3 from Asia, and one from the United States) belonged to the B/Yamagata lineage.
In other words, 7 out of 8 Influenza B viruses sampled over the summer don't match this year's vaccine.
It must be remembered that these samplings represent only a minute fraction of the number of cases of influenza over the past few months, and may not be predictive of our upcoming season.
How all of this will work out over this flu season remains to be seen. This past summer has been a rough flu season south of the equator, with South Africa, New Zealand, and Australia all reporting unusually severe influenzas this year. Again, not predictive, but certainly a cause for concern.
Even if this year's vaccine isn't a perfect match for the influenzas circulating this winter, authorities still are recommending that people avail themselves of the flu shots.
Again from Promed-mail:
Although many of the recently examined influenza A (H3) viruses show reduced reactivity with sera produced against the A/Wisconsin/67/2005 (H3N2) vaccine strain (the H3N2 component of the 2007-08 influenza vaccine), vaccination is still the best means of protection against influenza and influenza-related complications.
Even in years in which the match between the vaccine strains and circulating strains is not exact and protection against illness is reduced, the vaccine can still mitigate the severity of illness and reduce the likelihood of severe outcomes such as hospitalization and death.
While this year's vaccine may not be the ideal match for what may be coming, I'll be rolling up my sleave anyway.
As an interesting aside, Promed also reports that 2 cases of novel influenza were reported this summer in the United States. (reformated for readability)
There were 2 cases of human infection with swine influenza virus reported in the United States during August [2007].
Although human infection with swine influenza is uncommon, sporadic cases occur in most years, usually among persons in direct contact with ill pigs or who have been in places where pigs might have been present (e.g., agricultural fairs, farms, or petting zoos).
The sporadic cases detected in recent years have not resulted in sustained human-to-human transmission or community outbreaks; however, human infections with swine influenza viruses or any other nonhuman or novel influenza virus should be identified quickly and investigated.
Clinicians should consider swine influenza A in the differential diagnosis among patients with influenza like illness (ILI) who have had recent contact with pigs.
And that was the summer that was.
