Intranasal or Intramuscular Injection: Which Flu Vaccine Provides Better Community Protection? – August 31, 2016

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A recently published study sought to determine which of two flu vaccines would provide better community protection when administered in children.

 

Influenza, commonly called the flu, is a contagious respiratory illness caused by the influenza virus. The elderly, pregnant women, people with health conditions, and children are among those who are more likely to acquire flu-related complications that may lead to hospitalization and even death. Previous studies suggest that children are also a key source of transmitting the flu to the community, marking the importance of vaccinating children during the flu season. Vaccinating children against the flu not only protects them, but it also provides an indirect benefit to the community through herd immunity. Herd immunity occurs when a large part of the population has become immune to a contagious disease and protects most of the community members against that disease as there is less opportunity for an outbreak. Since children have been identified as an important source for community transmission of the flu, those vaccinated will help contribute to herd protection. However, researchers remain uncertain of which vaccine best achieves herd protection.

A recently published study in the journal Annals of Internal Medicine investigated two vaccines in particular: Intranasal live attenuated influenza vaccine (LAIV) and inactivated influenza vaccine (IIV). The researchers sought to determine which of the two vaccines would provide better community protection when administered in children and adolescents. They hypothesized that LAIV would reduce laboratory-confirmed influenza by 50% as opposed to IIV.

For the study, they investigated residents of 52 Hutterite colonies within 150 kilometers of designated cities or towns in Alberta and Saskatchewan, Canada. Hutterite colonies are small communities, usually around 70-120 residents, with single-family dwellings and communally-shared buildings. It is also where influenza is regularly introduced.

The participants of the study included healthy Hutterite children between the ages of 36 months to 15 years old. All other residents of the communities were also eligible to participate as non-vaccine recipients. In total, 4611 community members enrolled in the study among the 52 colonies. The researchers employed a cluster randomized blinded trial in which they randomly assigned participants into one of the two study groups: LAIV or IIV. The LAIV group received a 0.2 mL dose of intranasal LAIV and the IIV group received a 0.5 mL intramuscular injection. As a blinded study, children in the LAIV group also received a saline injection to mimic IIV, and children in the IIV group also received an intranasal saline to mimic LAIV. Nurses also prepared vaccines behind a privacy screen and surveillance staff who assessed the participants were not involved in vaccination and were also blinded to the allocated groups. Investigators, study coordinators, study monitors, and the data and safety monitoring board were also all blinded.

The researchers assessed the participants twice weekly for any symptoms or signs of the flu. For those with two or more signs and symptoms, the flu was confirmed on the basis of detecting the virus from respiratory samples. The flu is caused mainly by two types of viruses: Influenza A and B.

Over the three-year study period, taking place between October 2012 and May 2015, the study revealed that influenza A or B virus infection occurred at a rate of 5.3% in the LAIV group and 5.2% in the IIV group. The authors of the published study conclude that there was not a significant difference in vaccinating children with LAIV or IIV in providing better community protection against the flu. They note that although the choice for a flu vaccine may depend on various factors, the data does not suggest any additional benefit of LAIV over IIV.

 

 

 

Written By: Jessica Gelar, HBSc



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