'Less precise' study offers another take on FluMist performance

A new study provides data showing the live attenuated inactive virus (LAIV) FluMist vaccine was effective in children during the 2015-16 flu season, seemingly contradicting work published 2 months ago that suggested the vaccine offered no protection to recipients in that age-group that year.

But the new study—published yesterday in Clinical Infectious Diseases—was smaller and less precise than the earlier study, according to a US flu expert involved in both studies.

Protection against all strains was 46%

To conduct the observational study, children ages 2 to 17 years who sought outpatient care for acute respiratory illness accompanied with a fever were tested for influenza and asked about vaccination status. A total of 1,012 children were enrolled at eight clinic sites. The majority (59%) were unvaccinated, 10% had received LAIV, and 31% received the inactivated influenza vaccine (IIV), of flu shot.

Researchers found that LAIV was 46% protective in US children against all influenza strains. IIV was 65% effective. LAIV vaccine effectiveness (VE) was found to be statistically insignificant, however, when it came to the 2009 H1N1 strain.

"Both LAIV and IIV were protective against any influenza strain in 2015–2016 and against influenza A (H1N1) pdm09 strains in children without a high-risk condition. However, only IIV provided significant protection against influenza A (H1N1) pdm09 strains in the total study population," the authors concluded.

The findings offer yet another take on the usefulness of LAIV, especially in children.  Since 2008, the CDC has recommended seasonal influenza vaccination for all children over the age of 6 months, and before 2014, LAIV was considered a superior vaccine for children. But the clinical studies on LAIV were conducted before the 2009 flu pandemic, and subsequent seasons have shown that the vaccine performs poorly against H1N1 in US patients.

The authors suggest their work demonstrates the vaccine was somewhat protective in children, and that antigenic drift in the H1N1 virus was responsible for the falling efficacy rates.

New study smaller, less precise

In August, the New England Journal of Medicine (NEJM) published a study showing that the LAIV offered no protection for children in 2015-16. And in June, the Centers for Disease Control and Prevention recommended for the second year in a row that the LAIV not be used.

Edward Belongia, MD, director of the Center for Clinical Epidemiology & Population Health at the Marshfield Clinic Research Institute in Wisconsin was an author on both the Clinical Infectious Diseases and NEJM studies, the latter of which employed the test-negative design. He said that the studies are not as discrepant as they may first appear.

"The NEJM study included a much bigger study population and did not require fever," said Belongia. "This current study was smaller and less precise. But no one is suggesting there isn't a problem with LAIV and H1N1."

In an accompanying commentary by Justin Ortiz, MD, MS, of the University of Maryland Center for Vaccine Development, wrote of the inherent challenge of making vaccine recommendations with imperfect, changing data. No data collected from observational studies can compete with those collected during randomized control trials (RCTs), said Ortiz, who was not involved in either study. But observational studies have informed flu policy much more than RCTs.

"Observational studies are valuable because they can assess the most important public health questions," Ortiz said. They offer a glimpse of "real time" performance of the vaccine, whereas influenza vaccine RCTs in the United States are conducted among "mostly outpatient … carefully selected populations" and are mostly done for vaccine licensure.

See also

Oct 4 Clin Infect Dis study

Aug 10 N Engl J Medstudy

Oct 4 Clin Infect Dis commentary 

Aug 10 CIDRAP News story "Study: Change in inhaled flu vaccine did not help in 2015-16"

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