Introduction: Despite clear health benefits, and Public Health Agency of Canada recommendations, vaccination rates among Canadian adults are low. Frequent patient contacts, wait times, and the availability of trained staff make the emergency department (ED) a potential location to target specific populations and administer vaccinations. We evaluated the feasibility of two strategies to administer the Tdap vaccine to adult patients presenting to a single referral ED. Methods: Two immunization strategies and a control group were randomly ordered from one to three. Data collection for group one started on study day one with data collection for groups two and three on study days two and three respectively. This sequence was repeated over 15 consecutive weekdays (Monday-Friday, 0730-1530), evenly assigning each group to 5 different days. On intervention days, adult patients were screened during the triage process for eligibility to receive the Tdap vaccine. An ED based (EDB) strategy offered patients vaccination during that visit. The second strategy offered eligible patients a public health referral (PHR) to receive the vaccine at a later date. On all study days, patient triage times (TT), as well as markers of ED efficiency (number of patient registrations, time to physician, length of stay, left without being seen, number of admissions, number of boarded patients) were recorded. Results: The primary outcome, the proportion of eligible adults immunized, was significantly higher at 66% (n=81) for the EDB strategy (228 screened, 122 eligible), compared with 21% (n=20) for the PHR strategy (217 screened, 94 eligible; x2 (2, n=216)=43.41, p<0.00001). In addition, 10 participants in the PHR group received a second vaccine (Pneumococcal (7), Influenza (2), Human Papillomavirus (1)). Reasons for vaccine ineligibility included having an up-to-date Tdap (EDB n=47 (21%), PHR n=46 (21%)) and being considered in too much distress by the triage nurse (EDB n=26 (11%), PHR n=19 (9%)). Triage time was less for the control group (M=5:55 [mins:secs], SD=2:48) than for the EDB (M=6:47, SD=3:12) and PHR (M=7:25, SD=2:45) strategies. Conclusion: An ED based screening and immunization strategy was highly effective in providing eligible adult patients with the Tdap vaccine. A resulting small increase in triage time was not clinically significant. Further studies are required to generalize these results.