Some of them faced very uncomfortable side effects after getting the second dose, including dizziness and nausea. Her's was different. McCown said she slept through multiple alarms sounding. But the professionals say there’s no need to worry. These side effects mean the COVID-19 vaccine is working by providing immunity to prevent severe infection. “When you complete the two-dose series within two to three weeks, this vaccine is amazing,” said John Vinson, CEO of Arkansas Pharmacists Association. “It has 100% effectiveness at preventing death.” The APA suggests people worried about possible side effects to schedule their vaccine on a weekend, but do not miss your second dose because it’s critical.