Something about flu shot recs confuse me...

[Clarity]

We took dd1 for her H1N1 booster yesterday and I was thinking today about her very first (regular) flu shot experience. She was about 18 months and I did not give her the booster shot - she just got an initial flu shot. The next year, she got one flu shot. This year, per recommendations, she received the H1N1 shot twice. (She did not receive the seasonal flu shot this year.)

I'm wondering....each year the flu strain is or could be different, is that not correct? So each year, the flu shot may or may not cover the strain that was active the prior year. Like this: http://www.californiahealthline.org/articles/2008/2/13/Current-Flu-Vaccine-Not-Protective-Against-Two-New-Strains-of-Virus.aspx?topicID=49

So why don't children have to receive a two shot sequence every year? I assume because there are some protections from the flu shot that was given the prior year even if the strain is not identical. And, if that's the case, why did they need a two shot sequence for H1N1? I've thought about this too much today. And, yes, I know "research showed a booster was necessary" but why? And then why isn't one necessary each year the strain is a bit different? Is it that H1N1 may well mutate but because the strains are related that next year there will be no need for an H1N1 booster?

I don't know enough about flu strains and vaccination protocol. I need to read up.

[vonfirmath]

H1N1 is significantly different from the other flu strains.

[moonsky]

I recalled the ped told me that children need 2 regular flu shots the first year. Then one shot the year after if they already got one last year.

As this is the first year we have H1N1 vaccines, kids need two shots. I assume they would need only a shot a year after if they alreay got one this year(I need to ask the ped at the next visit).