Lots of information floating around this past week about influenza. Of anything, remember this: it’s easiest to predict that influenza can be unpredictable and it’s also still true that a flu shot is the best way to protect your family from flu. I’ll explain why, along with a recap of what you should know about new data, here.
Flu season is just getting started in the United States (circulating infections in nearly all states) and this past week the CDC announced new information about a strain of Influenza A, H3N2. This is exactly what the CDC is supposed to do: keep us informed and help us prepare for an influenza season. This year the information standing out is risks surrounding the strain of H3N2 that has “drifted” and the reality that when H3N2 is the most common strain of flu going around it tends to cause more serious infections.
When Influenza Virus “Drifts”
- Vaccines for each year’s flu are formulated months in advance to allow time for vaccine manufacturing and distribution.
- 100 centers around the world provide influenza surveillance and predict which strains will circulate to the US and North America. Decisions are made in February each year for the next year’s vaccine. Researchers look at trends to determine which viruses may be more prevalent.
- The vaccine protects against three (trivalent vaccine) or four flu viruses (quadrivalent vaccine), based on the world’s predictions. Typically each flu vaccine has at least two strains of Influenza A and one or two strains of Influenza B. Of anything that is consistent it’s that flu seasons are unpredictable.
- H3N2 is one strain of Influenza A in this year’s vaccine. The “drifted” vaccine is just another form of H3N2 that has different characteristics.
- Flu viruses often “drift,” this happens every few years. The drifted H3N2 virus is one specific type selected for the 2015 southern hemisphere influenza vaccine (point being: this isn’t an unknown virus, it was just unknown how much it would spread in the US).