Does the Flu Vaccine Really Protect Kids?

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http://www.time.com/time/health/article/0,8599,1847794,00.html

Monday, Oct. 06, 2008

Does the Flu Vaccine Really Protect Kids?

By Alice Park

Getting a flu shot is an annual rite of passage - or at least, according to

U.S. health officials, it should be. For the first time, the Centers for

Disease Control and Prevention (CDC) recommends this year that all children

aged six months through 18 years receive the flu vaccine; previous

advisories included children only up to five years old.

Government data indicate that the flu shot is more necessary than ever. The

rate of flu deaths among children, while not high, are continuing to rise -

more than 80 deaths were recorded in the 2007-2008 flu season, according to

the CDC - highlighting the potential benefit of vaccination.

Yet a new study published Oct. 6 in the Archives of Pediatrics & Adolescent

Medicine suggests otherwise - that the flu shot in children doesn't

necessarily protect them from illness. Led by Dr. Szilagyi,

researchers at University of Rochester studied 414 children aged 5 and

younger, who came down with the flu during the 2003-2004 or 2004-2005 flu

seasons. These children were compared with over 5,000 controls who did not

have influenza during the same seasons. Turns out that flu shots seemed not

to make much difference: Kids who got immunized did not get the flu at lower

rates than unvaccinated kids. In fact, the immunized youngsters were just as

likely to be hospitalized or to visit the doctor as kids who never received

the vaccine.

But before you decide to skip the flu shot this year, experts warn that

results of flu studies like this are all about design. Depending on how a

particular trial is set up - which populations are studied, which vaccine is

used and how many subjects are included - the results can vary, and quite

significantly. The Rochester study, for example, happened to look at the

effectiveness of a vaccine during two seasons in which the flu strain

included in the vaccine was not well matched to the predominant circulating

strain that was making people sick. That could explain the lack of

protection among the vaccinees - the shot may have been protecting against

the wrong flu proteins. Targeting the correct strain is a always a bit of a

guessing game, however; researchers make their best scientifically based

prediction as to which flu virus will be making the rounds in a coming

season, but they often have to make these predictions up to nine months

ahead of time, in order to keep up with the lengthy vaccine manufacturing

process. " In some circumstances, it is like forecasting the weather, " says

Dr. Geoffrey Weinberg, professor of pediatrics at University of Rochester.

" Sometimes we are right on, and sometimes we are off. "

Another reason for the flu shot's failure may have been the fact that

certain forms of the vaccine are more effective than others in children. In

this study, most of the children received the injected vaccine, but recent

studies have shown that the nasal spray, known as FluMist, appears to be

better at protecting youngsters from influenza (offering about the same

level of protection as the injected vaccine in adults). In kids, says Dr.

Schaffner of Vanderbilt University School of Medicine and an

advisory member of the CDC's Advisory Committee on Immunization Practices,

the nasal spray may help the immune system launch a broader and more diverse

immune defense, since the vaccine contains weakened forms of live flu virus

that replicate rapidly in the mucosal tissues. Such furiously multiplying

viruses may actually benefit vaccine effectiveness in flu seasons like those

included in the study, when there is significant mismatch - or " drift " -

between the circulating flu strains and the vaccine strains, because the

faster the viruses divide, the more likely they are to develop more

mutations, some of which may actually end up matching those circulating in

the community.

Finally, notes Weinberg, who was not involved in the new study but is

familiar with its design and results, the lack of effectiveness could have

been due in part to the trial's small sample size. " The bigger numbers you

have, the better, " he says. " Five hundred subjects may sound like a lot, but

once you start stratifying them by age, by whether they received all of

their shots, or which year they were immunized, your total number gets

smaller. "

All of which means that, as this study's results show, we need to become

more realistic when it comes to our expectations of the annual flu shot.

There is no guarantee that it will work, but on a population level, odds are

that it's better to get a flu shot than not. " We all recognize that the

influenza vaccine is not as effective as the polio vaccine, or the measles

vaccine, " says Schaffner. " It's not a great vaccine, but it is quite a good

vaccine. We are not going to eliminate influenza through the use of this

vaccine. But we can mitigate its devastating impact on the population if we

get immunized. "