NACI Literature Review on the Comparative Effectiveness and Immunogenicity of Subunit and Split Virus Inactivated Influenza Vaccines in Adults 65 Years of Age and Older
Subunit and split virus inactivated influenza vaccines are two commonly used types of seasonal influenza vaccines, and continue to dominate the market in Canada. Although these two formulations of influenza vaccine have been available for many decades, NACI has not previously conducted a literature review to investigate the comparative vaccine effectiveness of these different formulations. A difference in vaccine effectiveness between these formulations would be especially important for older adults (65 years of age or older), since there is evidence that older adults experience more severe illness due to influenza and have reduced vaccine effectiveness compared to younger adults. To address this gap, NACI conducted a literature review to examine the vaccine effectiveness and immunogenicity of unadjuvanted, standard dose subunit inactivated influenza vaccines compared to unadjuvanted, standard dose split virus inactivated influenza vaccines in adults 65 years of age and older. Eight studies were identified which assessed either the vaccine effectiveness or immunogenicity of subunit compared with split virus inactivated influenza vaccines. Included studies did not show statistically significant differences in vaccine effectiveness or immunogenicity. Methodological limitations and/or study quality was a concern for all included studies. NACI concludes that there is insufficient evidence to determine the comparative vaccine effectiveness and immunogenicity of unadjuvanted subunit and split virus inactivated influenza vaccines in adults 65 years of age and older (Grade I Evidence). The evidence is not sufficient to support specific recommendations on the differential use of subunit and split virus inactivated influenza vaccines in older adults.
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