The CDC's Advisory Committee on Immunization Practices (ACIP) recommendation regarding use of live attenuated influenza vaccine (LAIV; FluMist) for children ages 2-8 just got more complicated. Recent developments, however, have not prompted any change to the ACIP's -- or the AAFP's -- recommendations for use of the vaccine.
During the ACIP's Oct. 29-30 meeting,(www.cdc.gov) participants reviewed data from the U.S. Flu Vaccine Effectiveness Network that suggested the LAIV vaccine was not effective against the influenza A (H1N1) virus among children during the 2013-14 influenza season. That's according to AAFP liaison to the ACIP Jamie Loehr, M.D., of Ithaca, N.Y.
This unexpected finding differed from previous study results that suggested LAIV was more effective than inactivated influenza vaccine (IIV) for younger children, said a statement(www.cdc.gov) the CDC released on Nov. 6.
According to that statement, the ACIP and the CDC have recommended since 2008 that all children ages 6 months and older (with rare exceptions) receive annual influenza vaccine using any licensed, age-appropriate vaccine.
- Participants at the Oct. 29-30 meeting of the Advisory Committee on Immunization Practices (ACIP) reviewed data suggesting the live attenuated influenza vaccine (LAIV) was not effective against the H1N1 virus in children during the 2013-14 influenza season.
- At its June 25-26 meeting, the ACIP voted to recommend that beginning with the 2014-15 influenza season, LAIV should be used preferentially for healthy children ages 2-8 years based on data showing it offered superior protection against influenza virus infection in young children compared with inactivated influenza vaccine.
- The CDC said so far this flu season, U.S. seasonal surveillance data indicate substantially greater circulation of H3N2 and B viruses and little circulation of H1N1 viruses.
But at its June 25-26 meeting, the ACIP recommended that beginning with the 2014-15 influenza season, LAIV should be used preferentially for healthy children ages 2-8 when immediately available and when no contraindications or precautions against its use exist. This decision was based on previous data(www.cdc.gov) showing that LAIV offered superior protection against influenza virus infection compared to IIV in young children. The AAFP followed suit, offering the same preferential recommendation for this age group.
Questions About Effectiveness
According to the CDC, the reasons behind LAIV's lack of effectiveness against H1N1 infection during the 2013-14 season are not yet fully understood.
"It is possible that results may be specific to the H1N1 component of LAIV," the CDC said. "Influenza H1N1 viruses predominated during the 2013-2014 season for the first time since their emergence in 2009 when they caused a pandemic. It also is possible -- though less likely -- that there is an unidentified issue with the study methods or analysis plan."
Loehr told AAFP News that data on LAIV from the early 2000s suggested it was more effective than IIV in fighting H1N1. Then, during the 2011-12 and 2012-13 seasons, evidence found its effectiveness was equivalent to that of the injectable vaccine. With the current report that LAIV was not as effective as IIV during the 2013-14 season, Loehr noted this could herald a true downward trend in LAIV effectiveness or could simply be an anomaly.
It's possible the dip in effectiveness could be due to manufacturing issues or poor thermostability of a portion of the vaccine's influenza A seed virus strain that only manifested this year, Loehr said, and FluMist manufacturer MedImmune has said it plans to use a different seed virus in the future. It also might be related to variances among individual lots of the LAIV vaccine, because the data showed some lots had greater efficacy than others.
2014-15 Flu Season
The LAIV vaccine effectiveness estimates for the 2013-14 season suggest that the vaccine may not protect children against H1N1 virus infection during the 2014-15 season, said the CDC, because the same H1N1 virus -- an A/California/7/2009 (H1N1)pdm09-like virus -- is included in this season's vaccine. LAIV is designed to protect against four influenza virus types: influenza A (H1N1), influenza A (H3N2) and two influenza B viruses.
Read AAFP Policy Statement on LAIV Use in Children
A new policy statement the Academy released on Nov. 12 clarifies issues related to the effectiveness of live attentuated influenza vaccine in children and reiterates the AAFP's preferential recommendaiton for its use at this time.
But the good news so far this flu season, said the CDC, is that U.S. seasonal surveillance data indicate substantially greater circulation of H3N2 and B viruses and little circulation of H1N1 viruses. Of the subtyped viruses reported to the CDC from the week ending Oct. 5 through the week ending Oct. 25, 387 (31 percent) have been H3N2 viruses, 387 (31 percent) have been influenza B viruses and 16 (1 percent) have been H1N1 viruses. Another 466 influenza A viruses were not subtyped, the agency explained.
As of Oct. 31, manufacturers reported having distributed more than 132 million doses(www.cdc.gov) of the 151 million to 156 million total doses of IIV and LAIV projected to be available for the U.S. market this season, the CDC report said.
MedImmune projected that as many as 18 million doses of LAIV would be produced for the United States this season. Vaccine uptake data for this season are not yet available, but past trends show that more than half of flu vaccine doses given to children are administered by the end of October, suggesting that many children may have already received their vaccines.
Given the convergence of all these factors, the ACIP has recommended no changes to the current influenza vaccination recommendations at this time.
At the upcoming Feb. 25-26 ACIP meeting, the group will re-evaluate its LAIV recommendation based on the previous evidence with the addition of preliminary data collected from the 2014-15 season and may adjust the recommendation accordingly.
According to Loehr, the ACIP recommendation on LAIV use could change any number of ways. The committee could reaffirm the current recommendation, cancel the preferential use recommendation because data continue to show LAIV does not work better against H1N1 than IIV or it could decide to recommend against LAIV use altogether.
"If (LAIV) really doesn't have effectiveness compared to the injection for H1N1, then you could easily say not only should we not be recommending it preferentially, we shouldn't be recommending it at all," he said.
But the fact remains, Loehr added, that LAIV tends to be easier than IIV to administer to children, is more widely accepted by them and has minimal side effects. In the absence of any clear reason to stop giving the vaccine, it's likely that it will continue to be used for these patients, he noted.
At some level, said Loehr, this instance shows that when supporting data changes, the CDC is willing to re-evaluate relevant decisions. But he is still concerned that conceding any given vaccine is less than effective is going to cause hesitation about vaccines in general.
In any event, Loehr suggests clinics wait until after the ACIP meeting in February to order their flu vaccines for the fall of 2015. If a change in recommendation occurs, providers could then adjust their orders for the 2015-16 season.
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