Combined, that's potentially 159 million Americans who are covered against a virus some are estimating will hit 40 percent of the U.S. population.
"This is a situation of supply and demand, and making sure we can have the vaccine go where it's needed most," said Dr. Anne Schuchat, the director of the national center for immunization and respiratory diseases.
There's new evidence pregnant women - whose immune systems are suppressed - have a much higher risk of severe complications and death from H1N1. A study released Wednesday found pregnant women are four times as likely to be hospitalized.
"Six percent of the deaths have been among pregnant women, that's a larger proportion than you'd expect given that only one percent of the population is pregnant at any time," said Dr. Denise Jamieson, with the CDC division of reproductive health.
Each of the pregnant women in the study who died first developed pneumonia, just like 27-year-old Katie Flyte, who was six months pregnant when she got this new flu - forcing doctors to deliver her baby prematurely. While newborn Abbey is thriving, Flyte's heart, lungs and kidneys are failing.
"She's got a long way to go," said Katie's husband Kenny Flyte. "So this is just the beginning."
In the meantime, research centers across country are looking for thousands of healthy volunteers to test the new flu vaccine.
The clinical trials are set to begin mid-August. Adults will be tested first, followed by the elderly. If proven safe, it will then be tested in babies and children.
The vaccine is being fast-tracked - as experts worry about a back-to-school resurgence of both the novel H1N1 - and the seasonal flu.
"We'll see comingling of two different flues this season," said Dr. Kenneth Bromberg. "It'll be like a bad seasonal flu, and we have to worry about high-risk groups."
How to treat sick kids now is also a concern as H1N1 has been sweeping through summer camps. While many children were given the medication Tamiflu to prevent the flu, experts warn it should be prescribed cautiously.
"We're going to induce resistance against Tamiflu," Bromberg warned. "We are going to run out of one of our weapons against the flu."
Experts agree pregnant women should be given antiviral treatment immediately, and not wait for confirmed H1N1 tests. It's most effective if taken within 48 hours of the first flu symptoms.