COVID-19 vaccines that reduce symptoms but do not block infection need higher coverage and faster rollout to achieve population impact

• DOI: 10.1101/2020.12.13.20248142
• Publication Date: 2020-12-17T06:23:24Z
• Authors: David A. Swan; Chloe Bracis; Holly Janes; Mia Moore; Laura Matrajt; Daniel B. Reeves; Eileen Burns; Deborah Donnell; Myron S. Cohen; Joshua T. Schiffer; Dobromir Dimitrov
• Keywords: Interim; Vaccine efficacy; Infectivity

Abstract Background Several COVID-19 vaccine candidates are in the final stage of testing. Interim trial results for two vaccines suggest at least 90% efficacy against symptomatic disease (VE DIS ). It remains unknown whether this is mediated predominately by lowering SARS-CoV-2 infection susceptibility ( VE SUSC ) or development symptoms after SYMP A with high but low has uncertain population impact. Methods We developed a mathematical model transmission, calibrated to demographic, physical distancing and epidemic data from King County, Washington. Different rollout scenarios starting December 2020 were simulated assuming different combinations resulting up 100% constant effects over 1 year. assumed no further increase despite expanding case numbers reduction infectivity upon conditional on presence symptoms. Proportions cumulative infections, hospitalizations deaths prevented year vaccination start reported. Results Rollouts 1M vaccinations (5,000 daily) using 50% projected prevent 30%-58% infections 38%-58% one In comparison, 47%-78% 58%-77% both cases, there greater if mostly . The use “symptom reducing” will require twice as many people vaccinated than “susceptibility same death Delaying 3 months decreases expected impact approximately 40%. Conclusions Vaccines which not infection, thereby shift asymptomatic fewer larger faster rollouts have impact, compared that reduce infection. If uncontrolled transmission across U.S. continues, then Spring 2021 provide only limited benefit.