That's a good point - and I just got through remarking how impressive it's been that they've manufactured so much vaccine, so quickly. To a laymen, you would think one of the first things you'd want to establish - from a public health perspective - is how long the infected stay contagious.
If this particular virus leaves the infected infectious longer than most other flu virus, it would go a long way to explaining why this particular strain appears to be more virulent.
Back in the spring they were saying that the kids were shedding the virus longer than normal. That was why they were being told to stay home 10 days and some schools closed for 2 weeks at a time.