Research article
H1N1 and Seasonal Influenza Vaccine Safety in the Vaccine Safety Datalink Project

https://doi.org/10.1016/j.amepre.2011.04.004Get rights and content

Background

The emergence of pandemic H1N1 influenza virus in early 2009 prompted the rapid licensure and use of H1N1 monovalent inactivated (MIV) and live, attenuated (LAMV) vaccines separate from seasonal trivalent inactivated (TIV) and live, attenuated (LAIV) influenza vaccines. A robust influenza immunization program in the U.S. requires ongoing monitoring of potential adverse events associated with vaccination.

Purpose

To prospectively conduct safety monitoring of H1N1 and seasonal influenza vaccines during the 2009–2010 season.

Methods

The Vaccine Safety Datalink (VSD) Project monitors ∼9.2 million members in eight U.S. medical care organizations. Electronic data on vaccines and pre-specified adverse events were updated and analyzed weekly for signal detection from November 2009 to April 2010 using either a self-controlled design or a current versus historical comparison. Statistical signals were further evaluated using alternative approaches to identify temporal clusters and to control for time-varying confounders.

Results

As of May 1, 2010, a total of 1,345,663 MIV, 267,715 LAMV, 2,741,150 TIV, and 157,838 LAIV doses were administered in VSD. No significant associations were noted during sequential analyses for Guillain–Barré syndrome, most other neurologic outcomes, and allergic and cardiac events. For MIV, a statistical signal was observed for Bell's palsy for adults aged ≥25 years on March 31, 2010, using the self-controlled approach. Subsequent analyses revealed no significant temporal cluster. Case-centered logistic regression adjusting for seasonality demonstrated an OR for Bell's palsy of 1.26 (95% CI=0.97, 1.63).

Conclusions

No major safety problems following H1N1 or seasonal influenza vaccines were detected in the 2009–2010 season in weekly sequential analyses. Seasonality likely contributed to the Bell's palsy signal following MIV. Prospective safety monitoring followed by rigorous signal refinement is critical to inform decision-making by regulatory and public health agencies.

Section snippets

Background

The emergence of a novel H1N1 influenza virus of swine origin in North America in April 2009 prompted the rapid development of new H1N1 vaccines, which became available for use in October 2009. While the initial uncertainty of how the novel H1N1 pandemic would evolve led to heightened concerns about disease prevention, public anxiety about the safety of novel H1N1 vaccines also became apparent.1 Given the prior experience with the 1976 swine influenza vaccination program, where an excess risk

Study Population

The Vaccine Safety Datalink Project is a collaboration among eight medical care organizations and CDC, which has performed population-based research on vaccine safety in the U.S. since 1990.6, 7 These organizations include Group Health Cooperative (Washington); Harvard Vanguard Medical Associates & Harvard Pilgrim Health Care (Massachusetts); HealthPartners Research Foundation (Minnesota); Kaiser Permanente of Colorado (Colorado); Kaiser Permanente of Northern California (California); Kaiser

Vaccine Doses

As of May 1, 2010, there were 1,345,663 individuals vaccinated with MIV, 2,741,150 with TIV, 267,715 with LAMV, and 157,838 with LAIV in the VSD population. The percentages of children and adults vaccinated by age group for H1N1 and for seasonal influenza are shown in Figure 1. Coverage rates by age group varied from 10% to 54% for H1N1 and 15% to 81% for seasonal vaccines. Seasonal influenza vaccination rates were higher than H1N1 vaccination rates in every age group. Seasonal influenza

Discussion

The VSD successfully conducted near–real time, prospective surveillance for adverse events following seasonal and H1N1 influenza vaccines. This served as a key component of public health efforts to protect the health of children and adults in the U.S. during the 2009–2010 influenza season. Prospective surveillance did not detect statistical signals for GBS, demyelinating disease, peripheral nervous system disorders, seizures, encephalomyelitis, ataxia, anaphylaxis, allergic reactions, cranial

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