Safety at 2009 mass vaccination clinics, compared with 2003–2009 standard vaccination clinics — Tri-County (Denver metropolitan region), Colorado

Background: Mass clinics are useful for vaccinating populations quickly. Comparisons of injury rates between regular and mass vaccination clinics have not been reported previously. We compared 7 years of injury data from regular Tri-County Health Department (TCHD) vaccination clinics, that administered, on average, 56,284 vaccinations/year (54,118 injections/year), with injury data collected at 2009 pandemic influenza A (H1N1) mass vaccination clinics, where 63,137 vaccinations (38,389 injections) were administered over a 6-week period. Methods: Regular vaccination clinic annual injury rates were calculated for January 1, 2003–December 31, 2009 using vaccination administration records and injury data identified from an incident log maintained for insurance purposes. Mass vaccination injury rates were calculated for November 5–December 19, 2009 using vaccination administration records and injury reports. When calculating needlestick injuries, the denominator only included injections. Student t testing was used to compare injury rates. Results: The overall injury rate for mass clinics (23.8/100,000) fell outside the 99.9% confidence interval (CI) of the average annual needlestick injury rate observed at regular clinics (9.5/100,000, CI 0.6–18.5). The needlestick injury rate for mass clinics (7.8/100,000) fell outside the 99.9% confidence interval of the average annual needlestick injury rate observed at regular clinics (1.6/100,000, CI 0–4.3). Conclusions: Injuries, including needlesticks, were more common during mass clinics than during regular clinics. A formal survey is underway to identify possible problems with the vaccination equipment, training, and processes. Survey results might evoke ideas for implementing targeted prevention interventions to reduce injury rates at future mass clinics.