Through the beginning of April, it recorded about 5 million people who skipped it because they think one dose provides enough protection or they're scared of symptoms.
"For those that do feel some symptoms, it's usually mild muscle ache, maybe a headache and feeling a little bit off," said Allina Health Dr. Kevin Best.
Dr. Best is urging people to get their second shot. He says consider the first dose like a blue print, while the second dose is the all-important practice run.