(CNN)A Colorado mass vaccination site paused operations this week after 11 people experienced adverse reactions to the Covid-19 vaccine.
More than 1,700 people received the Johnson & Johnson vaccine on Wednesday at Dick's Sporting Goods Park, a soccer stadium where the state of Colorado and health care provider Centura Health operate a mass vaccination site. The 11 people reported feeling nauseous and dizzy after they were vaccinated, Colorado health officials said.
Two of the patients were transported to a hospital "out of an abundance of caution," while the other nine were given juice and water to recover, according to a statement from the Colorado State Joint Information Center.
Officials didn't elaborate on the two hospital patients' conditions.
"The state has no reason to believe that people who were vaccinated today at Dick's Sporting Goods Park should be concerned," state health officials said.
The site closed early on Wednesday afternoon, before another 640 people were scheduled to receive their vaccine. Their appointments have been rescheduled to Sunday, Centura Health said.
Despite the hospital transport, the side effects the 11 patients reported were "consistent with what can be expected" from the Johnson & Johnson vaccine, Covid-19 Incident Commander Scott Bookman said in a statement.
"We know it can be alarming to hear about people getting transported to the hospital, and we want to assure Coloradoans that the CDC and public health are closely monitoring all the authorized vaccines continually," Bookman said. "Based on everything we know, it remains true that the best vaccine to get is the one you can get the soonest."
Severe side effects from Covid-19 vaccines are rare
It's relatively common to experience side effects from any of the three vaccines available in the US -- about 10% to 15% of volunteers in vaccine trials developed "quite noticeable side effects," former Operation Warp Speed Chief Scientific Adviser Moncef Slaoui said late last year.
The most common side effects are arm soreness, fatigue, body aches and, in some cases, a low-grade fever. Nausea, like the 11 patients in Colorado experienced, headaches and swelling at the injection site may occur, too, according to the US Centers for Disease Control and Prevention.
Severe side effects, like an allergic reaction, are far less common, occurring around every two to five per million people, Baylor College of Medicine dean Dr. Peter Hotez told CNN earlier this month.
Johnson & Johnson vaccine is effective
Health officials continue to combat the stigma that Johnson & Johnson is a lesser vaccine than the Moderna and Pfizer two-shot offerings, which a recent CDC study found are 90% effective at preventing Covid-19. Johnson & Johnson's vaccine was found to be 66% effective in preventing moderate to severe illness.
It's difficult to draw comparisons between Johnson & Johnson and the two-shot alternatives, though, because the Johnson & Johnson vaccine was studied after highly contagious variants of coronavirus were discovered, said Dr. Leana Wen, a CNN medical analyst. The vaccine was found to be effective in preventing severe disease in South Africa, where a contagious variant became dominant, and no patients who received the vaccine were hospitalized or died.
"Having a vaccine that is clearly effective against this type of mutation is a distinct advantage," she told CNN in March.