Meet the new flu, same as the old flu*

Next year we’ll be back to one flu vaccine, thank goodness. The flu vaccine protects you against three different strains of the influenza virus, but for the past year, we had a separate vaccine for the new pandemic (“swine”) flu. It’s always hard to get people to take their shots (or “jabs,” as they say in England – why can’t we come up with a less painful-sounding word?), and asking everyone to go out and get two shots was never ideal.

For the next flu season, the vaccine will include these 3 strains:

1. The 2009 “swine flu” strain, H1N1
2. The previous seasonal flu, H3N2
3. Influenza B, a milder flu that has been around for decades.

What happened? Well, the WHO, the CDC, and the FDA have decided to replace one of the three strains in the flu vaccine with the new H1N1. The strain they replaced was also called H1N1, which is rather confusing. Let’s look at the history of these strains, which is an interesting picture of virus evolution.

In 1918, the Spanish flu (which originated in the U.S., despite its name) spread throughout the world and killed an estimated 30-40 million people, in the worst flu epidemic in recorded history. This was the original H1N1 flu. It soon evolved into a milder flu, which was around until...

In 1957, a new pandemic strain appeared, H2N2 or "Asian flu." This completely replaced H1N1 in the human population, although H1N1 continued to fluorish in pigs (more on that below). H2N2 dominated until...

In 1968, the Hong Kong flu pandemic, H3N2, swept the world and replaced H2N2.

Then, very suspicously, in 1977 the H1N1 strain reappeared in Russia. It is widely believed that this was an accidental escape from the Soviet Union’s biowarfare program. This H1N1 strain didn’t replace H3N2, but both strains have co-circulated ever since, with H3N2 generally causing more serious illness.

All along, the milder influenza B strain has been around as well. That’s why the vaccine contains 3 strains: H3N2 (from 1968), H1N1 (from 1918 via Russia in 1977), and flu B.

That brings us to late 2008. Several strains of Spanish flu (H1N1) had been circulating in pigs for decades. Two of those strains combined to create the new pandemic flu, which jumped from pigs to humans. Oddly enough, we don’t have any reports of a pandemic among pigs, which is why “swine flu” is a misnomer. Here are the latest statistics for human infections in the U.S., for the last week of March 2010:

• 3.7% of people tested turned out to have influenza. (In other words, the season is over, as I predicted in mid-January.)
• 98% of positive influenza specimens were pandemic H1N1.
• 2% of positive specimens were influenza B.

So it seems that the swine flu has replaced the Russian flu. At least it has in the vaccine. It might even be safe to get rid of H3N2 in the vaccine, but there’s little harm in keeping it in the vaccine for one more season, just in case H3N2 stays with us a bit longer. So next fall we’ll be back to one shot, and “pandemic flu” will be just plain old “seasonal flu” once again.

The CDC's advisory panel also (rather quietly) expanded their recommendation on who should get vaccinated “to include all people aged 6 months and older.” That’s right, everyone, even the elderly. Wait until the anti-vaccination movement gets hold of this – they’ll have a field day. Actually I’m surprised they haven’t already. Maybe they don’t know about the nanobots we’ll be putting in vaccines in the very near future.

*with apologies to The Who.