Analysis of past studies shows benefit of inactivated influenza vaccine against A/H1N1pdm09 virus in 2- to 17-year-olds.
A flu shot was more effective than nasal spray in protecting children aged 2 to 17 years old against a widely circulating type of influenza, according to a recent study that included more than 17,000 young people from 42 US states.
To reach that conclusion, investigators looked to previously reported data from 5 US studies that covered the influenza seasons from 2013-2014 through 2015-2016.
These studies considered the viral effectiveness (VE) of inactivated influenza vaccine (IIV), administered as a shot, and quadrivalent live attenuated vaccine (LAIV4), delivered as a nasal spray known as FluMist.
The current mega-analysis mirrored previous results. Investigators reported 67% effectiveness for the IIV shot versus 20% effectiveness for the LAIV4 spray against influenza A/H1N1pdm09, the main type of flu in the US this season.
“The findings of lower effectiveness of LAIV compared to IIV against A/H1N1pdm09 virus in the US are consistent with the findings from the individual studies,” lead author Jessie R. Chung, MPH, an epidemiologist in the US Centers for Disease Control and Prevention’s (CDC’s) Influenza Division, told MD Magazine®.
When the team analyzed the 2 vaccines’ effectiveness against any type of influenza, the difference was less pronounced: 51% VE for IIV and 26% for LAIV4. The study also suggested a possible but non-significant benefit of LAIV4 over IIV against influenza B viruses.
“The vaccines provided similar protection against A (H3N2) and B viruses,” Chung said.
The US Advisory Committee on Immunization Practices (ACIP) and the American Academy of Pediatrics (AAP) recommended against using the nasal spray for young children in the 2016—17 and 2017–18 flu seasons because of concerns about its earlier effectiveness
However, Chung noted that LAIV has been updated since then.
The spray was used in Europe and Canada in 2017—2018, although limited circulation of the A/H1N1pdm09 virus hindered the ability to obtain precise effectiveness estimates. According to information from the UK though, the US can expect more favorable results.
“VE estimates against H1N1 last season in the UK are encouraging and suggest effectiveness of LAIV against that virus in the US will be higher this season,” Chung said.
The ACIP has reinstated the recommendation for use of LAIV4 in the US for the current influenza season as 1 vaccine choice. The AAP recommends the inactivated influenza vaccine as the primary choice for all children because of past effectiveness questions and lack of current data on LAIV4.
However, the AAP said LAIV4 may be offered for children who would not otherwise receive an influenza vaccine, and for whom it is appropriate by age and health status, according to its website.
“LAIV is again an option for this season for patients aged 2-49 years who would prefer to receive the nasal spray vaccine,” Chung said. Influenza vaccinations can reduce the risk of flu-associated hospitalization and can be life-saving in children, she stressed.
“Parents should know that the most important thing they can do to protect their child against influenza is to vaccinate him or her,” she said.
She added that the CDC recommends annual influenza vaccination for everyone 6 months and older with any licensed, age-appropriate flu vaccine (IIV, RIV4, or LAIV4) with no preference expressed for any 1 vaccine over another.
RIV4 is a recombinant egg-free vaccine known as Flublok Quadrivalent, which is delivered as a shot to adults aged 18 years and older, according to the CDC.
While the new vaccine effectiveness analysis drew similar conclusions to the 5 individual studies, Chung noted that the latest investigation provided more depth.
“The current study better described vaccine effectiveness in age groups that the individual studies were not able to due to small sample sizes,” she said.
The study, titled, “Live Attenuated and Inactivated Influenza Vaccine Effectiveness,” was published online American Academy of Pediatrics.