I found an open data set that includes around 29544 DNA sequences of the influenza virus. Each sequence looks something like the following:

>gi|60698|gb|X58690|Influenza A virus (A/FPV/Rostock/34(H71)) gene for cap-binding protein PB2, genomic RA [Seq Num 23]
>
>GAGAGAGTGG TCGTGAGTAT TGACCGTTTC TTAAGAGTTC GAGATCAGCG
>
>TGGAAATGTA ATCCTGTCTC CTGAAGAGGT TAGCGAAACG CAGGGAACAG

Where the top portion is a header for each sequence. What is the header describing exactly?

Why are GC and AT base pairs so important?

Lastly, how can we apply the knowledge of knowing the DNA sequence of so many influenza viruses to enhance medical intervention?

Edit: Formatting