Prevalence of seroprotection against the pandemic (H1N1) virus after the 2009 pandemic

• Published in: Canadian Medical Association journal (CMAJ) Vol. 182; no. 17; pp. 1851 - 1856
• Main Authors: Skowronski, Danuta M, Hottes, Travis S, Janjua, Naveed Z, Purych, Dale, Sabaiduc, Suzana, Chan, Tracy, De Serres, Gaston, Gardy, Jennifer, McElhaney, Janet E, Patrick, David M, Petric, Martin
• Format: Journal Article
• Language: English
• Published: Canada CMA Impact Inc 23.11.2010; CMA Joule Inc; CMA Impact, Inc; Canadian Medical Association
• Subjects: Adolescent; Adult; Age Factors; Aged; Aged, 80 and over; Antibodies, Viral - blood; Antibodies, Viral - immunology; Body fluids; British Columbia - epidemiology; Care and treatment; Child; Child, Preschool; Female; Hemagglutination Inhibition Tests; Humans; Infant; Influenza A Virus, H1N1 Subtype - immunology; Influenza Vaccines - immunology; Influenza Vaccines - therapeutic use; Influenza, Human - immunology; Influenza, Human - prevention & control; Male; Middle Aged; Pandemics; Pandemics - prevention & control; Pandemics - statistics & numerical data; Patient outcomes; Physiological aspects; Prevalence studies (Epidemiology); Studies; Swine flu; Swine influenza; Vaccination - statistics & numerical data; Young Adult; British Columbia; Canada; British Columbia Canada
• ISSN: 0820-3946; 1488-2329
• DOI: 10.1503/cmaj.100910

Before pandemic (H1N1) 2009, less than 10% of serum samples collected from all age groups in the Lower Mainland of British Columbia, Canada, showed seroprotection against the pandemic (H1N1) 2009 virus, except those from very elderly people. We reassessed this profile of seroprotection by age in the same region six months after the fall 2009 pandemic and vaccination campaign. We evaluated 100 anonymized serum samples per 10-year age group based on convenience sampling. We measured levels of antibody against the pandemic virus by hemagglutination inhibition and microneutralization assays. We assessed geometric mean titres and the proportion of people with seroprotective antibody levels (hemagglutination inhibition titre ≥ 40). We performed sensitivity analyses to evaluate titre thresholds of 80, 20 and 10. Serum samples from 1127 people aged 9 months to 101 years were obtained. The overall age-standardized proportion of people with seroprotective antibody levels was 46%. A U-shaped age distribution was identified regardless of assay or titre threshold applied. Among those less than 20 years old and those 80 years and older, the prevalence of seroprotection was comparably high at about 70%. Seroprotection was 44% among those aged 20-49 and 30% among those 50-79 years. It was lowest among people aged 70-79 years (21%) and highest among those 90 years and older (88%). We measured much higher levels of seroprotection after the 2009 pandemic compared than before the pandemic, with a U-shaped age distribution now evident. These findings, particularly the low levels of seroprotection among people aged 50-79 years, should be confirmed in other settings and closer to the influenza season.