The rates of infection with the influenza virus in the United States continue to climb, as expected at this time of year.

Before going further, we should repeat that there are many viruses that cause viral respiratory infections, and in fact, so far this year the number of such colds and flus due to the influenza virus has reached 30%, so over 2/3 of all colds and flus still are not from the influenza virus.

Now, on to the latest on the influenza virus.

We have talked before about how the influenza virus changes every spring as it leaves the human community, and every late fall when it returns to us. Sometimes the influenza virus that actually appears completely matches the subtypes in that winter’s vaccine, sometimes not so much.

The current data suggest that the dominant strain appearing in the US is indeed the H3N2 strain, and it is different than the H3N2 in the flu spray and flu shot, that is, the flu vaccines for the winter of 2015.

We now know the following details on how well this year’s flu vaccines protect against the H3N2 out there:

• About 50% of the H3N2 circulating do match what’s in the flu vaccine, and those vaccinated are protected very well against it.
• About 50% of the H3N2 circulating do not fully match what’s in the flu vaccine, but match well enough to blunt the severity of the infection.

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