Seroprevalence Following the Second Wave of Pandemic 2009 H1N1 Influenza

Abstract

BACKGROUND: In April 2009, a new pandemic strain of influenza infected thousands of persons in Mexico and the United States and spread rapidly worldwide. During the ensuing summer months, cases ebbed in the Northern Hemisphere while the Southern Hemisphere experienced a typical influenza season dominated by the novel strain. In the fall, a second wave of pandemic H1N1 swept through the United States, peaking in most parts of the country by mid October and returning to baseline levels by early December. The objective was to determine the seroprevalence of antibodies against the pandemic 2009 H1N1 influenza strain by decade of birth among Pittsburgh-area residents. METHODS AND FINDINGS: Anonymous blood samples were obtained from clinical laboratories and categorized by decade of birth from 1920-2009. Using hemagglutination-inhibition assays, approximately 100 samples per decade (n= 846) were tested from blood samples drawn on hospital and clinic patients in mid-November and early December 2009. Age specific seroprevalences against pandemic H1N1 (A/California/7/2009) were measured and compared to seroprevalences against H1N1 strains that had previously circulated in the population in 2007, 1957, and 1918. (A/Brisbane/59/2007, A/Denver/1/1957, and A/South Carolina/1/1918). Stored serum samples from healthy, young adults from 2008 were used as a control group (n=100). Seroprevalences against pandemic 2009 H1N1 influenza varied by age group, with children age 10-19 years having the highest seroprevalence (45%), and persons age 70-79 years having the lowest (5%). The baseline seroprevalence among control samples from 18-24 year-olds was 6%. Overall seroprevalence against pandemic H1N1 across all age groups was approximately 21%. CONCLUSIONS: After the peak of the second wave of 2009 H1N1, HAI seroprevalence results suggest that 21% of persons in the Pittsburgh area had become infected and developed immunity. Extrapolating to the entire US population, we estimate that at least 63 million persons became infected in 2009. As was observed among clinical cases, this sero-epidemiological study revealed highest infection rates among school-age children.

Influenza Virus H1N1pdm09 Infections in the Young and Old: Evidence of Greater Antibody Diversity and Affinity for the Hemagglutinin Globular Head Domain (HA1 Domain) in the Elderly than in Young Adults and Children

“…The HI titers postinfection were not statistically different among the various age groups (Table 1), in agreement with previous studies (36,41). Furthermore, when available, prepandemic HI titers against A/California/07/2009 in samples collected in March 2009 were Ͻ10 for the different age groups analyzed in this study (30). Since we were interested in comparing the epitope diversity recognized by elderly subjects with that recognized by the most naïve populations, we initially pooled serum samples from three age groups, 0 to 9 years, 10 to 19 years, and 70 to 89 years, for GFPDL analyses.…”

“…No information is available in regard to other comorbidities for these individuals. Sera were obtained from hospital laboratories and tested to find those that had antibody to pandemic H1N1 during the second wave of pH1N1 infections in 2009 (30). None of the donors were vaccinated with pH1N1, since no pH1N1 vaccine was available in the city at the time of collection.…”

“…The samples were collected anonymously from extra laboratory specimens at the University of Pittsburgh Medical Center's (UPMC) Presbyterian Hospital and the Children's Hospital of Pittsburgh (30,41).…”

Epidemiological and Clinical Characteristics of Pandemic Influenza A (H1N1)v Infection Among the Children Admitted to Suleyman Demirel University

“…İmmün yetmezlikli hastalarda veya süt çocuklarında inkübasyon süresi daha uzun olabilmektedir (11,16). Bulaş yolları kontamine eller, damlacık teması ve havada asılı partiküllerin teması ile olmaktadır (14,17). H1N1v pozitif hastalarımızın %44,4"ünde şüpheli temas öyküsü bulunmakta ve kaybedilen iki olgunun da evde influenza benzeri semptomları olan kişilerle teması bulunmaktaydı.…”

“…Salgınların daha çok okul çağı çocuklarında, okulların açık olduğu dönemde görüldüğü tespit edilmiştir (17,23). Bu çalışmada ise H1N1v pozitif hastaların yaş ortalaması 32 ay olarak bulunmuştur.…”