Flu shots more effective than nasal sprays

To determine the effectiveness of the flu shots, researchers based at the University of Michigan carried out a clinical experiment on 1,952 adults aged 18 to 49 by giving them either an injected flu vaccine, a placebo injection, a flu vaccine nasal spray or a placebo nasal spray during the 2007-2008 flu season.

Placebo is an inert sugar pill administered to the patient who’s not told about the pill being inert. Such an intervention may cause the patient to believe that the treatment will change his/her condition, which may, in turn, result in a therapeutic effect in improving his/her condition.

Analysis of the experiment revealed to the researchers that the injection was 50 percent better in preventing the flu than the nasal spray.

Injected flu vaccine’s better results vis-à-vis nasal sprays
Tracking the medical condition of the participants for one year, the researchers found some suspected cases of influenza- marked by muscle aches, headache, nasal congestion, nausea, and vomiting- in about 119 participants.

The findings of the study suggested that volunteers who had received the injected flu vaccine were 68 percent less likely to have flu than those who got the placebo injection. And those who had received the nasal spray vaccine were 36 percent less likely to get the flu than those who received a placebo.

"The nasal spray vaccine is effective but isn't as effective as the injected vaccine," said lead study author Arnold S. Monto, an epidemiology professor at the University of Michigan School of Public Health.

"But it's better to get some vaccine than no vaccine, so if you're averse to getting an injection, get the nasal spray,” he added.

However, the researchers stressed on the fact that their findings were applicable only for adults as the vaccines were not tested on children. They said that the same results may not hold true for children, who may respond just as well to a nasal spray vaccine.

Lead researcher Monto also noted that it is yet not clear that the findings of the study will hold true for the pandemic swine flu as well.

Why flu shot works better than nasal spray in adults?
There are two different types of flu vaccines, called live attenuated-- which contain very weakened or modified live virus, and inactivated--which contain bits of dead virus.

The nasal spray is made of live attenuated influenza vaccine which provokes the immune system to produce antibodies against the virus.

The researchers found that the live attenuated virus may not be strong enough to cause that response in adults who may already have some immunity against the flu strains.

Whereas, children are more likely to lack natural antibodies to the virus so like the flu shot, the nasal spray may prove equally effective for them.

The study appears in the journal New England Journal of Medicine.