My four-year-old got her swine flu vaccination yesterday. At the time, I was relieved when the school nurse pulled out a spray rather than a syringe.

There were no tears — or at least fewer than if she had gotten a shot.

But then I started to wonder — is this really as good as the real thing … that is, the needle?

Apparently I'm not alone. My neighborhood parent list serve has been peppered with posts from parents wondering the same thing.

"Why is the H1N1 vaccine being given as nasal spray rather than a shot?" asks one mother.

"Is this just to keep kids from freaking out?" posed another.

So I did a bit of digging around to try and find out if the spray delivery, while easier and less painful, is as effective. The answer, like so much in science, appears to be mixed.

A Sept. 24, 2009 report in the New England Journal of Medicine showed the injectable vaccine for seasonal influenza offered 50 percent better protection than the live nasal spray vaccine during the 2007-08 flu season.

But (and this is a big but for parents) that study was only among a sample of 2,000 young adults, ages 18 to 49.

Other clinical trials have found the nasal spray to be more effective than injectable shots in children. Their immunity to flu viruses appeared to last longer and their blood levels showed higher levels of antibodies.

Why would children respond differently to these vaccines than adults?

Scientists aren't sure, but it probably has to do with the fact that the spray delivers a debilitated, but live form of the virus for the body's immune system to respond to, while the shot injects a dead bit of virus into muscle.

"It may be a situation where adults are already naturally immunized to more viruses," explained Lone Simonson, a disease researcher at George Washington University's School of Public Health and Health Services. "So their immune systems may not respond as readily to the live virus."

Then again, Simonson argues that as long as the immune system responds to a spray vaccine (and children's systems seem more likely to), then it can offer fuller protection. That's because the live virus form in the spray triggers the body to respond to the entire virus, rather than to just the dead virus parts delivered by a shot.

Not everyone is advised to get the spray, however, since it is a live virus. The Centers for Disease Control advises pregnant women and people (including children) with asthma and other health conditions to get the injectable vaccine.

Simonson explains this is because they want to eliminate any risk that the live vaccine causes a real infection.

"For those other than in those groups, the spray poses no additional risk than the injectable," she said.

All this left me thinking the nose spray may have been the better choice after all for my daughter. And it didn't even hurt!

photo credit: Associated Press