Influenza Vaccination Is Not Associated With Detection of Noninfluenza Respiratory Viruses in Seasonal Studies of Influenza Vaccine Effectiveness

Maria E. Sundaram 2 3 David L. McClure 2 3 Jeffrey J. VanWormer 2 3 Thomas C. Friedrich 0 1 2 Jennifer K. Meece 2 3 Edward A. Belongia () 2 3 0 Wisconsin National Primate Research Center , Madison, Wisconsin 1 Department of Pathobiological Sciences, University of Wisconsin School of Veterinary Medicine 2 Received 5 April 2013; accepted 23 May 2013; electronically published 6 June 2013. WI 54449 3 Marshfield Clinic Research Foundation , Marshfield Background. The test-negative control study design is the basis for observational studies of influenza vaccine effectiveness (VE). Recent studies have suggested that influenza vaccination increases the risk of noninfluenza respiratory virus infection. Such an effect could create bias in VE studies using influenza-negative controls. We investigated the association between influenza infection, vaccination, and detection of other respiratory viruses among children <5 years old and adults 50 years old with acute respiratory illness who participated in seasonal studies of influenza vaccine effectiveness. Methods. Nasal/nasopharyngeal samples collected from 2004-2005 through 2009-2010 were tested for 19 respiratory virus targets using a multiplex reverse-transcription polymerase chain reaction (RT-PCR) platform. Vaccination status was determined using a validated registry. Adjusted odds ratios for influenza and vaccination status were calculated using three different control groups: influenza-negative, other respiratory virus positive, and pan-negative. Results. Influenza was detected in 12% of 2010 children and 20% of 1738 adults. Noninfluenza respiratory viruses were detected in 70% of children and 38% of adults without influenza. The proportion vaccinated did not vary between virus-positive controls and pan-negative controls in children (P = .62) or adults (P = .33). Influenza infection was associated with reduced odds of vaccination, but adjusted odds ratios differed by no more than 0.02 when the analysis used influenza-negative or virus-positive controls. Conclusions. Influenza vaccination was not associated with detection of noninfluenza respiratory viruses. Use of influenza-negative controls did not generate a biased estimate of vaccine effectiveness due to an effect of vaccination on other respiratory virus infections. The case vs test-negative control study design is the basis for observational studies of influenza vaccine effectiveness (VE) [1-6]. Cases and controls are recruited at the time of presentation of acute respiratory illness Influenza VE and Nonspecific Immunity - (ARI) in clinic and hospital settings. Individuals presenting with ARI who test positive for influenza are considered cases, whereas those who test negative for influenza are considered controls. This study design is convenient to implement and inherently accounts for potential confounding due to differences in healthcareseeking behavior between vaccinated and unvaccinated individuals [13]. It has recently been suggested that influenza vaccination may increase the risk of non-influenza respiratory virus infection by decreasing temporary nonspecific immunity [7, 8]. One proposed mechanism involves activation of the innate immune response following influenza infection, leading to a temporary reduction in the risk of infection with a different respiratory virus. By reducing the risk of influenza infection, the influenza vaccine could paradoxically create an increased risk of infection with other noninfluenza respiratory viruses. If this phenomenon occurs, it could lead to biased estimates of influenza vaccine effectiveness in studies using laboratory-confirmed influenza cases and influenza-negative controls. In this scenario, the risk of noninfluenza viral illness would be higher in vaccinated than unvaccinated individuals, and an influenza-negative control group would therefore have a higher proportion of vaccinated individuals compared to the source population. This could theoretically contribute to overestimation of true VE (ie, bias away from the null); therefore, a key assumption of the test-negative control design of influenza vaccine effectiveness studies is that the proportion of noninfluenza viral illness does not differ by influenza vaccination status [9]. The goals of this study were to determine if influenza vaccination is associated with detection of noninfluenza respiratory viruses and to determine if vaccine effectiveness estimates differ when different control groups are used in the analysis. To achieve these goals, we analyzed available data from members of a community cohort who saw a physician for acute respiratory illness and consented to participate in a study of influenza vaccine effectiveness over 6 influenza seasons. The vaccine effectiveness study enrolled individuals of all ages (with some variation by season), but this analysis was restricted to children <5 years old and adults 50 years old. For participants in these age groups, multiplex reverse transcription polymerase chain reaction (RT-PCR) testing was subsequently performed to detect other respiratory viruses, providing an opportunity to investigate the relationship between influenza vaccination and infection with other viral pathogens. Young children and older adults are among the most vulnerable individuals to influenza infection and complications [10, 11] and calculating influenza vaccine effectiveness in these groups is therefore of high importance [12]. Participants and Setting The Marshfield Clinic Research Foundation has conducted sea sonal studies of influenza vaccine effectiveness in a Wisconsin population cohort since the 20042005 season. The details of the seasonal studies have been reported elsewhere [2, 3]. Briefly, patients with ARI were recruited during each influenza season in primary care clinics, urgent care, emergency department, and an acute care hospital. Symptom eligibility criteria varied by season but included fever/feverishness or cough during most seasons. Individuals with illness duration 10 days (20042005 through 20062007) or >7 days (20072008 through 2009 2010) were excluded to minimize false negative RT-PCR results. After obtaining informed consent, a nasal swab (children <12 years old) or a nasopharyngeal swab (adolescents and adults) was obtained and placed in viral transport media for influenza testing. Symptoms and onset date were assessed during the enrollment interview. Real-time RT-PCR was performed each season to identify influenza cases. After testing was complete, aliquots of samples in viral transport media were frozen at 80C. This study was reviewed and approved by the Marshfield Clinic Institutional Review Board. During each season, all study participants (or parents) provided informed consent for influenza testing. Multiplex RT-PCR testing to detect additional viruses was subsequently approved by the IRB with a waiver of informed consent. Laboratory Archived samples were tested for the presence of respiratory virus nucle (...truncated)