For season flu use antivirals regardless of vaccination status

The 2012/2013 seasonal influenza vaccine is moderately effective at preventing medically attended influenza. However, some vaccinated people may still become infected, so clinicians should use antivirals as recommended by CDC regardless of vaccination status, according to estimates published in Morbidity and Mortality Weekly Report (MMWR), February 22, 2013.

The study results represent pooled analyses using subjects enrolled at 5 study sites, including Group Health, in Seattle.

“Our contribution was enrolling, interviewing, and getting lab test results for 263 subjects,” Michael L. Jackson, PhD, MPH, assistant scientific investigator, Group Health Research Institute, told Formulary.

At Group Health, researchers estimated influenza vaccine effectiveness (VE) at preventing medically attended influenza (ie, influenza that's severe enough to result in a doctor's visit).

At all 5 study sites, a method called the "test-negative" design was used to estimate how well the vaccine works.

“In this design, we enroll people seeking care for influenza-like illness,” Dr Jackson said. “We then test all enrolled subjects for influenza. We estimate VE by comparing the distribution of vaccination in people with lab-confirmed influenza with the distribution in people who test negative for influenza.

“We found that overall, people who were vaccinated were 56% less likely to have medically attended influenza than unvaccinated people,” Dr Jackson said.

The vaccine had basically the same level of effectiveness against the dominant strains of influenza circulating this year (influenza A(H3N2) and influenza B), and had basically the same level of effectiveness across different age groups, according to Jackson. “The exception was that the vaccine appears to be poorly effective against the A(H3N2) strain in adults 65 years old and older.”