Because they're considered to be the most vulnerable, doctors recommend that all kids get vaccinated against the H1N1 flu virus. But what about children who have chronic health conditions?

Asthma, cancer and Crohn's disease affect millions of kids in the U.S. Some parents, and even doctors, are confused about what to do.

Of the millions who will go to the doctor for an H1N1 vaccine, this visit probably means more to 11-year-old Grant Powell and his mom than it does most.

Grant has Crohn's disease and the only way for him to control it is to take powerful medicine that weakens his immune system.  That leaves him at a higher risk of infection, especially since he's a hockey player and sharing things like locker rooms, handshakes, even water bottles.

"This is the first time that we've gone into a flu season and he's actually been taking immunosuppressants. So I really don't know what to expect," Grant's mom, Lisa Arledge Powell, said.

Neither do a lot of other parents. It's estimated some 5 million kids are on immunosuppressant drugs for everything from asthma to AIDs, from cancer to Crohns.

And specialists have been flooded with calls from parents and doctors, asking the same question: should kids on immunosuppressant drugs get the vaccine?  Dr. Dennis Cunningham says yes, but with conditions.

"It's important that these patients get the flu shot. The injection that goes right into the arm, rather than the flu mist," Cunningham said.

The mist is actually made from a live virus and kids on immunosuppressants should not take it.

Cunningham and his colleagues are set to launch a new government-funded study on immune responses to the H1N1 virus. But in the meantime, he says not only should patients get the shot, but their families should too.

"The whole idea of that is called the ring vaccination. Put a ring of people around the vulnerable patient who are vaccinated so that they will not bring the virus into the home and then infect the patient," Cunningham said.

Experts say if your child is on immunosuppressants, they don't respond fully to the H1N1 vaccine, but some protection is better than none.