A mass vaccination site temporarily shut down Wednesday in Denver after 18 vaccine recipients suffered adverse side effects.

The clinic administered more than 1,700 shots of the Johnson & Johnson vaccine Wednesday prior to the pause, local CBS affiliate KCNC reported. The reactions occurred at Dick’s Sporting Goods Park, home of MLS’ Colorado Rapids, which opened March 22 as a vaccine site.

18 out of more than 1700 works out just a hair over one percent.