# 4787
One of the lessons of this recent pandemic flu outbreak is that influenza isn’t very good at following a script.
Assumptions based on events past don’t always prove valid.
In early 2009, few would have hazarded a prediction that H1N1 would spark the next pandemic outbreak, or that it would emerge from pigs, and evolve in our own backyard.
And once H1N1 took off last summer and fall, many expected the virus to completely replace the existing seasonal influenza A viruses – as had happened after the pandemics of 1918, 1957, and 1968.
And for a time, that appeared to be what was happening. Reports of seasonal H1N1 were almost nil, and seasonal H3N2 around the world were rare.
But lurking in the shadows was a new strain of H3N2, one that was detected about the same time as novel H1N1 emerged.
This variant called A/Perth/16/2009-like H3N2 wasn’t covered by last year’s flu vaccine, and has only been circulating for a little over a year, and so much of the world’s population is likely susceptible.
Still . . . reports of H3N2 over the past year have been sporadic, and widely scattered. A few blogs on these reports from the past couple of months include:
Singapore: H1N1 No Longer Dominant Strain
Global Flu Activity Update
Transitions: 3 Global Snapshots Of Flu Activity
Flu: Down, But Not Completely Out
H3N2 has often been associated with more severe flu seasons, and unlike the novel h1N1 virus, is perfectly capable of infecting the elderly – who traditionally see the greatest impact from seasonal influenza each year.
The good news is, antigens for this new strain are in this year’s trivalent flu vaccine, along with pandemic H1N1, and a B strain.
Whether this H3N2 virus has `legs’ or not, and ends up having a big impact on this year’s flu season, is impossible to know right now.
But the fact that immunity to this strain in the community is probably very low, and the virus continues to circulate, suggests that it might.
The CDC released a HAN (Health Alert Network) Message earlier this week on the recent detection of H3N2 in the United States. Robert Roos of CIDRAP News has more details in H3N2 flu outbreaks, cases trigger CDC alert while I’ve posted the opening to the CDC’s Health Alert below.
This is an official
CDC HEALTH ADVISORYDistributed via Health Alert Network
Wednesday, August 04, 2010, 19:55 EDT (7:55 PM EDT)
CDCHAN-00316-2010-08-04-ADV-NSeasonal Influenza A (H3N2) Virus Infections
Summary
Influenza A (H3N2) virus infections have been recently detected in people in a number of states across the U.S., including two small localized outbreaks. Sporadic cases of influenza and localized summer outbreaks from seasonal influenza viruses are detected each summer.
Clinicians are reminded to consider influenza as a possible diagnosis when evaluating patients with acute respiratory illnesses, including pneumonia, even during the summer months. Treatment decisions should not be made on the basis of a negative rapid influenza diagnostic test result since the test has only moderate sensitivity. False positive results also can occur, particularly at times when overall influenza prevalence is low.
For patients for whom laboratory confirmation is desired, or to confirm initial influenza cases in a community in which cases have been tested by rapid influenza diagnostic tests, it is recommended that reverse transcriptase -polymerase chain reaction (RT-PCR), and/or viral culture is utilized. Clinicians should use empirical treatment with influenza antiviral medications for persons hospitalized with suspected influenza, and for suspected influenza infection of any severity in high-risk individuals, regardless of influenza immunization status.
Early initiation of treatment provides more optimal clinical responses, although treatment of moderate, severe, or progressive disease begun after 48 hours of symptoms can still provide benefit.
