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A vaccine that protects children against four strains of flu may be more effective than the usual three-strain vaccine, a new study suggests.
The four-strain (or so-called "quadrivalent") vaccine is available as a nasal spray or an injection for the first time this flu season. The injected version, however, may be in short supply, according to the U.S. Centers for Disease Control and Prevention.
The study of about 200 children did not compare the four-strain vaccine to the traditional three-strain vaccine. Rather, it looked at how kids responded either to the four-strain vaccine or a hepatitis A vaccine, and then compared response rates for the four-strain flu vaccine to response rates for the three-strain vaccine from last year's flu season.
"This is the first large, randomized, controlled trial to demonstrate the efficacy of a quadrivalent flu vaccine against influenza in children," said study co-author Dr. Ghassan Dbaibo.
"The results showed that, by preventing moderate to severe influenza, vaccination achieved reductions [of 61 percent to 77 percent] in doctors' visits, hospitalizations, absences from school and parental absences from work," said Dbaibo, at the department of pediatrics and adolescent medicine at the American University of Beirut Medical Center, in Lebanon.
The results confirm the effectiveness of the vaccine against influenza, and particularly against moderate to severe influenza, Dbaibo said.
"They also showed an 80 percent reduction in lower respiratory tract infections, which is the most common serious outcome of influenza. Therefore, vaccination of children in this age group can help to reduce the significant burden placed on parents, doctors and hospitals every flu season," he said.
The report was published online Dec. 11 in the New England Journal of Medicine. The study was funded by GlaxoSmithKline, maker of the four-strain vaccine used in the study.
Dr. Lisa Grohskopf, a medical officer in CDC's influenza division, said there are several flu vaccine options for children.
For children aged 2 and up, a nasal spray is an option, and for children under 2, the usual injection is available, she said.
"The nasal spray vaccine is a quadrivalent vaccine, which has four different flu viruses in it. That's to increase the likelihood of whatever might be circulating during the season," Grohskopf said.
The flu shot is available with either three or four virus strains, she said.
"Since quadrivalent vaccines are new this year, there's not as much of them being produced as trivalent vaccines -- for the flu shots -- so there may be places where it's harder to get the quadrivalent vaccine," Grohskopf said.
The four-strain vaccine may cost a little more than the trivalent [three-strain] vaccine, but cost will vary by location, she said. And the vaccine is covered by insurance.
According to the CDC, 138 million to 145 million doses of flu vaccine will be available this year. An estimated 30 million to 32 million of these doses will be the four-strain flu vaccine. The rest will be the three-strain vaccine.
The three-strain vaccine protects against two types of influenza A -- H1N1 and H3N2 -- and one B strain. The four-strain vaccine adds another B strain.
Grohskopf said, because of the short supply of the four-strain vaccine, the CDC is not recommending one vaccine over another.
"The most important thing is that kids get a flu vaccine, even if it's the older trivalent one," she said.
Two doses of vaccine are recommended for children 6 months to 2 years of age who are getting vaccinated for the first time, Grohskopf said. "They need to get those doses before flu season is really in full swing," she said.
The effectiveness of the vaccine depends on how well it is matched to the circulating viruses. And it's still too early in the flu season to tell just how effective either vaccine will be, Grohskopf said.
For the study, Dbaibo and colleagues assigned 62 children aged 3 to 8 to receive the four-strain vaccine and 148 to receive a hepatitis A vaccine.
They found, among the children exposed to the flu, 16 of those who received the four-strain flu vaccine got sick, compared with 61 of those who got the hepatitis A vaccine. These numbers indicate the vaccine was 74 percent effective in preventing flu.
In contrast, last year's flu vaccine, which contained three strains of flu, was 56 percent effective, according to the CDC.
In the new study, side effects were similar in both the flu and hepatitis A groups. Serious side effects occurred in 1.4 percent of those who received the flu vaccine and in 0.9 percent of those who received the hepatitis A vaccine. The most serious side effects were one case of bronchitis and a case of convulsions in the flu vaccine group.
To learn more about flu, visit the U.S. Centers for Disease Control and Prevention.