Infectious disease specialist explains why AstraZeneca's COVID-19 vaccine can vary in effectiveness
7:28pm PST - November 23rd, 2020 astrazeneca - CBS NewsAstraZeneca announced Monday that its COVID-19 vaccine is up to 90% effective and even shows signs of reducing asymptomatic spread. It's effectiveness varied during clinical trials, depending on the dosage, but still averaged 70%. Dr. Uzma Syed, an infection …