A study published online in Annals of Internal Medicine(annals.org) on Aug. 16 found that children immunized in Hutterite communities in Canada using the live attenuated influenza vaccine (LAIV) were protected equally as well as those given the standard inactivated influenza vaccine (IIV).
The study was conducted during the 2012-2013 through 2014-2015 influenza seasons and, thus, predated the period from which the CDC's Advisory Committee on Immunization Practices (ACIP) drew data used to formulate its recent recommendation against the use of LAIV during the 2016-2017 flu season.
Jennifer Frost, M.D., medical director for the AAFP Health of the Public and Science Division, told AAFP News, "For the 2015-2016 flu season, (the ACIP) reviewed data from more than 2,000 children who received the flu vaccine and were diagnosed with influenza. These data showed a relative ineffectiveness of LAIV."
Frost said there are studies, such as this one, from past flu seasons that indicate LAIV was at least as effective as IIV in reducing the risk of influenza. "However," she added, "until a reason is found for LAIV's ineffectiveness this past season, (the AAFP) agrees that it should not be used."
- A recent study found that children immunized during the 2012-2013 through 2014-2015 influenza seasons in Canadian Hutterite communities were equally protected by the live attenuated influenza vaccine (LAIV) compared with the standard inactivated influenza vaccine.
- The study period predated that from which the CDC's Advisory Committee on Immunization Practices drew data it used to formulate its recent recommendation against using LAIV during the 2016-2017 flu season.
- Until a reason is found for LAIV's ineffectiveness during the 2015-2016 season, the AAFP agrees with the CDC that it should not be used.
Furthermore, Frost noted, the study examined a specific population of Hutterite children in Canada, which limits its generalizability to the U.S. population.
Researchers conducted a cluster randomized blinded trial in 52 Hutterite colonies around Alberta and Saskatchewan, Canada, enrolling volunteers and following them from Oct. 22, 2012, through May 20, 2015.
These communities were chosen for the study because they are relatively isolated from cities and towns, allowing researchers to randomly assign the children of entire communities to vaccination with either LAIV or IIV. This, in turn, permitted them to better assess the comparative effects of each vaccine type on both direct and herd immunity, which they collectively termed "community protection."
The researchers randomly assigned 1,186 children to receive LAIV and 3,425 children to receive IIV. The children ranged in age from 36 months to 15 years, and distribution by age was similar between the two groups. For each of the three flu seasons covered by the study, children in the groups received either the LAIV or IIV vaccine formulation recommended for that season.
To maintain blinding, children randomized to receive LAIV were given a concurrent 0.5-ml saline injection to mimic IIV; those who received IIV also were administered a 0.2-ml dose of intranasal saline.
Influenza surveillance began when one or more cases of laboratory-confirmed influenza over two consecutive weeks occurred at least two weeks after participant vaccination in a study colony was completed. The children were assessed twice weekly using a standardized checklist of self- or parent-reported symptoms or signs.
If any flu symptoms were reported, the participant was contacted directly by research staff who then obtained flocked nasal swabs if two or more of the following signs or symptoms were present: fever greater than or equal to 100.4 F, cough, nasal congestion, sore throat, headache, sinus problems, muscle aches, fatigue, earache or infection, or chills.
Mean vaccine coverage achieved during the study period was 76.7 percent among children in the LAIV group versus 72.4 percent among those in the IIV group. Comparative rates of influenza A or B virus infection were 5.3 percent in the LAIV group and 5.2 percent in the IIV group. Of those infected, 3.4 percent in the LAIV group and 3.3 percent in the IIV group had influenza A virus, while 1.9 percent in the LAIV group and 2 percent in the IIV group had influenza B virus.
Of participants in the LAIV group who contracted influenza A, about 45 percent had H3N2 and about 55 percent had H1N1 (from the 2013-2014 influenza season). Those with influenza A in the IIV group had a similar H3N2/H1N1 distribution.
Overall, the researchers found that in addition to LAIV providing similar direct protection compared with IIV, it also created comparable herd immunity.
The ultimate takeaway, according to Frost, is that although influenza vaccination is crucial to flu prevention, it's not a perfect science.
"Every season, different flu strains dominate, and vaccine manufacturers continue to produce new and 'better' vaccines," she said. "The CDC reviews the data available to make evidence-informed recommendations."
LAIV is still being used in other countries, Frost pointed out, and CDC officials will continue to monitor its effectiveness there.
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