Effectiveness of Non-Adjuvanted Pandemic Influenza A Vaccines for Preventing Pandemic Influenza Acute Respiratory Illness Visits in 4 U.S. Communities

Abstract

We estimated the effectiveness of four monovalent pandemic influenza A (H1N1) vaccines (three unadjuvanted inactivated, one live attenuated) available in the U.S. during the pandemic. Patients with acute respiratory illness presenting to inpatient and outpatient facilities affiliated with four collaborating institutions were prospectively recruited, consented, and tested for influenza. Analyses were restricted to October 2009 through April 2010, when pandemic vaccine was available. Patients testing positive for pandemic influenza by real-time RT-PCR were cases; those testing negative were controls. Vaccine effectiveness was estimated in logistic regression models adjusted for study community, patient age, timing of illness, insurance status, enrollment site, and presence of high-risk medical conditions. Pandemic virus was detected in 1,011 (15%) of 6,757 enrolled patients. Fifteen (1%) of 1,011 influenza positive cases and 1,042 (18%) of 5,746 test-negative controls had record-verified pandemic vaccination >14 days prior to illness onset. Adjusted effectiveness (95% confidence interval) for pandemic vaccines combined was 56% (23%, 75%). Adjusted effectiveness for inactivated vaccines alone (79% of total) was 62% (25%, 81%) overall and 32% (−92%, 76%), 89% (15%, 99%), and −6% (−231%, 66%) in those aged 0.5 to 9, 10 to 49, and 50+ years, respectively. Effectiveness for the live attenuated vaccine in those aged 2 to 49 years was only demonstrated if vaccination >7 rather than >14 days prior to illness onset was considered (61%∶ 12%, 82%). Inactivated non-adjuvanted pandemic vaccines offered significant protection against confirmed pandemic influenza-associated medical care visits in young adults.

Interim estimates of 2013/14 vaccine effectiveness against influenza A(H1N1)pdm09 from Canada’s sentinel surveillance network, January 2014

“…Our point estimate of ca 75% VE for the 2013/14 nonadjuvanted TIV against influenza A(H1N1)pdm09 is comparable, if not exceeding, 2009 estimates for nonadjuvanted formulations of the monovalent pandemic vaccine used in the US (ca 60%) [26,27], albeit lower than the 93% VE estimated by our sentinel system for the 2009 AS03-adjuvanted pandemic vaccine used in Canada [10]. The 2013/14 mid-season VE estimate against influenza A(H1N1)pdm09 of ca 75% is in the upper range of recent seasons' VE estimates for nonadjuvanted TIV against A(H1N1)pdm09 reported since 2010 from Canada [11,12,21], Europe [28][29][30][31][32] and the US [33][34][35], which span ca 60-80%.…”

The first, second and third wave of pandemic influenza A (H1N1)pdm09 in North Denmark Region 2009–2011: a population‐based study of hospitalizations

“…Surveillance data from Denmark and North Denmark Region report an uptake in risk groups of 50% and 48%, respectively, in 2010,5 and a recent Danish study found that only 10 of 53 patients admitted to ICUs in 2009–2010 had been vaccinated, mostly due to chronic co‐morbidities 1. The role of vaccination is unclear at the individual level, but effectiveness at the public health level varying from 49% to 93% is reported in recent studies from the US, Canada, and Australia11, 12, 13; hence, the importance is acknowledged by WHO.…”

Demographic distribution and transmission potential of influenza A and 2009 pandemic influenza A H1N1 in pilgrims

“…The demographic variables that could affect the distribution of influenza A infections in populations are gender [16][17][18][19], age [15], clinical signs [20], vaccination against flu [21], usage of antimicrobials [22,24], smoking habits [25,29], and ethnicity [30,31].…”