COVID vaccinations have taken off in the U.S. over the last six months. More than 321 million doses have been administered throughout the country—and a majority of those have been the two-dose Pfizer or Moderna vaccines. Over 176 million doses of Pfizer and 132 million doses of Moderna have been given, according to the latest data from the Centers for Disease Control and Prevention (CDC). Unfortunately, more people getting these two vaccines means that more people are at risk for making a major mistake with their vaccination. The CDC says more than 1 in 10 people who got the Pfizer or Moderna vaccine have missed their second dose, even though both vaccines require two doses for full vaccination.

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Per the CDC, about 88 percent of those who received one dose of the Pfizer or Moderna vaccine have completed their two-dose series as of June 16, according to data shared with CNN. This means that more than 1 in 10 people eligible to do so have not gotten their second shot. This number has grown, as just around 8 percent were missing their second dose as of March.

The New York Times reported that there are various reasons why people have missed their second dose. Some are reportedly nervous for worse side effects associated with the second shot, while others have said they felt protected enough with just the first jab.

According to the CDC, you should get the second dose of Pfizer 21 days after the first and the second dose of Moderna 26 days after the first. "You should get your second shot as close to the recommended three-week or four-week interval as possible," the CDC says. However, the agency also says that "your second dose may be given up to six weeks (42 days) after the first dose, if necessary."

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As CNN reports, around 1.5 percent of people who got one shot are still in the "allowable interval" of 42 days, per the CDC. But nearly 11 percent of those eligible have exceeded that deadline. "There is currently limited information on the effectiveness of receiving your second shot earlier than recommended or later than six weeks after the first shot," the CDC explains.

Many experts say that making sure you get two doses is even more important as COVID variants, like the Delta variant, continue to spread. A recent study from Public Health England published June 22 found that Pfizer's vaccine was 88 percent effective against the Delta variant two weeks after the second dose, but only 33 percent effective after just one dose.

"I will say, as worrisome as this Delta strain is with regard to its hyper-transmissibility, our vaccines work," CDC director Rochelle Walensky, MD, said during a June 18 interview on Good Morning America. "So I would encourage all Americans, get your first shot and when you're due for your second, get your second shot and you'll be protected against this Delta variant."

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