Cell culture-based, standard inactivated flu vaccine provide same effectiveness against H1N1
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Data from two test-negative design studies demonstrated similar vaccine effectiveness with a cell culture-based inactivated influenza vaccine and a standard inactivated influenza vaccine against laboratory-confirmed influenza A/H1N1.
The findings were presented during the Virtual Annual Conference on Vaccinology Research sponsored by the National Foundation for Infectious Diseases.
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“Eggs have been used for global influenza vaccine production since the 1950s, but egg-based vaccine strains can contribute to reduced vaccine effectiveness, especially for influenza A-H3N2,” Kayla Hanson, MPH, epidemiologist at Marshfield Clinic Research Institute, told Healio.
According to Hanson, there are currently two influenza vaccine products available in the United States that are manufactured without eggs Flucelvax and Flublok.
“Real world vaccine performance is assessed annually, but often these studies don’t look at specific vaccine products,” Hanson added. “We conducted this study to assess the effectiveness of Flucelvax against medically attended, laboratory-confirmed influenza specific to the 2018-2019 influenza season.”
Hanson and colleagues pooled data from two separate test-negative design studies of influenza vaccine effectiveness conducted by Marshfield Clinic Research Institute in Wisconsin during the 2018-2019 influenza seasons. The first, a single-site study, estimated cell culture-based inactivated influenza vaccine (ccIIV4) effectiveness among individuals aged 4 years and older (ccIIV4 study). The second was a study conducted by the CDC-funded U.S. Influenza Vaccine Effectiveness Network (Flu VE study), where only data from patients aged 4 years and older enrolled by Marshfield Clinic Research Institute were included.
Study procedures were similar in both investigations. Research staff approached participants between Dec. 26, 2018 and April 26, 2019 during outpatient primary and urgent care visits for acute respiratory illness (ARI). Participants with ARI were only eligible for the study if they had a cough with an illness duration equal to or less than 7 days and had not taken an antiviral agent.
Hanson and colleagues estimated the effectiveness of ccIIV4 by comparing the odds of ccIIV4 vaccination vs. no vaccination among influenza-positive and influenza-negative participants. They assessed relative vaccine effectiveness of ccIIV4 vs. IIV4 by comparing the odds of receiving ccIIV4 vs. IIV4 among influenza-positive vs. influenza-negative participants.
In total, 2,464 participants were included 31% from the ccIIV4 study and 68% from the Flu VE study. The mean age was 35 years; most participants were male (60%) and non-Hispanic white (90%).
Overall, 31% of all participants tested positive for influenza 57% for influenza A/H1N1pdm09 and 41% for influenza A/H3N2. Approximately half of participants (47%) were vaccinated; 67% received ccIIV4 and 18% received IIV4.
Overall, the study showed that ccIIV4 effectiveness against A/H3N2 was 20% (95% CI, –9%-41%) and 46% (95% CI, 18%-65%) among children aged 4 to 17 years, whereas IIV4 effectiveness against A/H3N2 was –27% (95% CI, –100%-20%) and 11% (95% CI, –66%-53%) among children aged 4-17 years. Relative vaccine effectiveness against A/H3N2 of ccIIV4 vs. IIV4 was 39% (95% CI, –19%-69%) in children aged 4-17 years.
The effectiveness of ccIIV4 against influenza A/H1N1pdm09 was 43% (95% CI, 26%-56%), 54% (95% CI, 27%-71%) among children aged 4 to 17 years, and 33% (95% CI, 5%-53%) among adults aged 18 to 64 years. IIV4 effectiveness against A/H1N1pdm09 was 49% (95% CI, 18%-68%), 63% (95% CI, 17%-83%) among children aged 4 to 17 years and 47% (95% CI, 2%-72%) among adults 18 to 64 years of age. The relative vaccine effectiveness of ccIIV4 vs. IIV4 against A/H1N1pdm09 was –12% (95% CI, 86%, 32%).
“We know that influenza vaccine effectiveness varies by season, subtype, age and product. Data from our observational study showed that the cell culture-based inactivated influenza vaccine is effective in preventing influenza, but we do need more studies to assess the effectiveness of this vaccine across seasons and to determine if egg-free vaccine products do provide better protection,” Hanson said. “Nevertheless, influenza vaccination remains our best strategy to prevent influenza and will be especially important this fall given the potential for co-circulation of influenza and COVID-19.”
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Hanson K, et al. Effectiveness of cell culture-based inactivated influenza vaccine against medically attended, laboratory-confirmed influenza in Northcentral Wisconsin, 2018-2019. Presented at: NFID Annual Conference on Vaccinology Research; June 18-19, 2020 (virtual meeting).
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