Your question brings up the issue of a possible pandemic. Pandemics result from the emergence, by antigenic shift, of an influenza A virus that people have not been exposed to and, therefore, do not have protective immunity against. However, in order for a new influenza virus to have the potential of becoming a pandemic, it must also be easily transmitted from person-to-person. I don't know the specifics on all the cases in Colorado but two had concominant bacterial infection, (bacterial tracheobronchitis) the combination of both is what made it especially lethal in these children and may not necessarily be a more virulent strain, although I doubt it.
I am worried the flu virus this year has undergone a antigenic shift rahter than the yearly drifts.
Influenza viruses undergo two kinds of change. One is a series of mutations over time that cause a gradual evolution of the virus, known as drift which results in the emergence of new strains. The other is an abrupt change in the surface proteins, known as antigenic shift which results in new subtypes of influenza A.
During this century, pandemics occurred in 1918, 1957, and 1968. In 1918, half a million people died in this country alone! On a yearly basis, appprox 35,000 people a year die making it one of the number one killers in winter months here in the US. Birds are the primary reservoir for new influenza viruses. All 15 recognized influenza A subtypes have been found in birds.
The pediatricians have been encouraging flu vaccines in those 2 years and younger since they are as likely to suffer serious consequences from the flu much like the elderly over 65. My two year old daughter has been vaccinated both years upon the recommendation of my pediatrician. I believe with the exception of an 8 yr old, the other deaths in Colorado were children close to two years of age or under. (Many pediatricians encourage vaccination after two years of age to dramatically reduce school absenteeism and overall sickness rates foor the kids in the school. But that is a matter of choice between the parents and their pediatricians.)
Although this years flu vaccine may not be the exact subtype, I still believe it will confer some cross protection (remember, almost every years flu vaccine is a close approximation due to the annual antigenic drift and changes on the surface proteins.) It may not protect you from getting the flu, but you may not be as likely to die or be hospitalised. Remember, it takes about three weeks to fully develop good immunity after the vaccination ( the dead, inactived intramuscular injection) so exposure to the flu within this window period may still mean you get the flu! (I am not sure about the live attenuated nasal flu vaccine that just came out this year.)
As for how these antigenic shifts and drifts occur I will leave that up to a cell biolgist since my brain is only partially functioning at this time of the night. Off to bed![zz)]
