Summer flu cases highlight importance of immunization

A cluster of unusual summer influenza cases in North Central Florida in recent weeks has highlighted the importance of vaccination and may provide evidence that a flu control program in Alachua County is working, University of Florida and Alachua County Health Department experts say.

Influenza typically peaks in February with few, if any, cases occurring during the summer months, according to the Centers for Disease Control and Prevention.

But since the end of May, nine patients with confirmed cases of influenza B and one with influenza A have been admitted to Shands at the University of Florida. None of the patients had been immunized for the flu this year, as far as officials can determine.

“We have seen a few more positives this week,” said Kathleen Ryan, M.D., a clinical associate professor of pediatrics in the UF College of Medicine and a member of the UF Emerging Pathogens Institute. “We have been in contact with the staff at the Alachua County Health Department, and they are helping with the investigation of the outbreak.”

The last outbreak of flu during the summer in North Central Florida was the H1N1 pandemic in 2009, Ryan said. The CDC estimates there were 274,000 hospitalizations and 12,470 deaths among all age groups nationwide related to H1N1 during the pandemic.

What makes the current cluster of cases particularly odd is that it involves influenza B, which is less common than influenza A, said Paul Myers, M.S., administrator for the Alachua County Health Department. The H1N1 virus, for example, was a form of influenza A.

“The good news is, influenza B is part of the flu vaccine, so if these patients had gotten the vaccine they would not have become ill,” Myers said.

Of the patients who have been admitted to the hospital for influenza since May, six of the nine infected with influenza B were from outside of Alachua County, which is home to a robust flu-prevention program.

The community-based Control Flu program offers free FluMist — a nasal spray influenza vaccine — to all elementary, middle and high school students in Alachua County. As a result of this program, 10,479 Alachua County schoolchildren were immunized for the flu in 2011.

“Alachua County residents seem to be better protected during this outbreak due to our high immunization rates through the Control Flu program,” Ryan said.

Although the program only supplies free nasal vaccine to children, the resulting increase in immunizations across the county helps protect the entire community, Myers said. By immunizing school-age children, who are “super spreaders” of the flu, people with chronic medical conditions or who are not immunized are less likely to encounter infected individuals. Also, infected people are less likely to pass on the virus if most of the people around them are immunized. Epidemiologists refer to this concept as herd immunity.

“Vaccination is the only primary means of preventing influenza infection,” Myers said. “It is effective. It is safe. It not only protects you, but also protects your loved ones and the community.”

The CDC recommends all adults and children over 6 months of age receive the flu vaccine each year. The recent cluster of influenza B cases highlights this need, Ryan said.

“We cannot afford to become complacent because influenza is serious,” Ryan said. “We cannot predict its activity, and we cannot predict when we will have another serious pandemic.”