There are two vaccines currently available in the U.S. that require two separate shots given weeks apart: Moderna and Pfizer. According to the CDC, you have to get both shots if you are getting either of these vaccines. Per the agency’s guidelines, you are only considered fully vaccinated two weeks after the second shot in the series. During an April 25 interview with CNN’s Jim Acosta, White House COVID adviser Anthony Fauci, MD, told Acosta that this is a recurring problem with two-dose vaccine processes. “Obviously whenever you have a two-dose vaccine, you’re going to see people who for one reason or other—convenience, forgetting, a number of other things—just don’t show up for the second vaccine,” Fauci said. And for more insight from the infectious disease expert, Dr. Fauci Says This Is How You Can Catch COVID Even If You’re Vaccinated. Unfortunately, millions of Americans have skipped their second dose of the vaccine. According to the most recent data from the CDC, nearly 8 percent of those who got a first dose of Pfizer or Moderna have missed their second shot. This is more than double the rate of missed second doses between December and February—indicating that more and more people may be forgoing the second shot, according to The New York Times. There are several reasons why people have skipped the second dose, the NYT reported. Some people who had bad side effects after the first fear worse reactions after the second, as side effects are generally more noticeable after the second shot. However, the CDC maintains, “You should get your second shot even if you have side effects after the first shot, unless a vaccination provider or your doctor tells you not to get it.” And for more CDC warnings, The CDC Says You Should Immediately Do This Once You’ve Been Vaccinated.ae0fcc31ae342fd3a1346ebb1f342fcb The NYT reported that some people have skipped their second shot because they felt they were sufficiently protected from a single dose. However, you’re more protected with two doses for both the Moderna and Pfizer vaccines. According to the U.S. Food and Drug Administration (FDA), the Pfizer vaccine is estimated to be only 82 percent effective after the first dose, but 95 percent effective a week after the second dose. For the Moderna vaccine, the FDA reported an estimated 80.2 percent efficacy after the first dose, and a 94.5 percent efficacy two weeks after the second dose. One of the largest concerns is that these data points were collected when the manufacturers submitted their vaccine for emergency-use authorization (EUA) in December, which means further data on the effectiveness of the vaccine for people who only received one dose isn’t yet available. Meanwhile, recent follow-up vaccination data for both Pfizer and Moderna showed that they both remain more than 90 percent effective against symptomatic and severe COVID for up to six months after someone receives their second dose. And for more up-to-date information, sign up for our daily newsletter. For the most part, there is only one reason you should skip your second shot. According to the CDC, you should not get the second dose of either Moderna or Pfizer if you had a severe or immediate allergic reaction to the first dose of the vaccine. “An allergic reaction is considered severe when a person needs to be treated with epinephrine or EpiPen or if they must go to the hospital,” the CDC says. “An immediate allergic reaction means a reaction within four hours of getting vaccinated, including symptoms such as hives, swelling, or wheezing (respiratory distress).” And for more on notable vaccine reactions, If 1 of These 3 Body Parts Starts Swelling Up After Your Vaccine, Call a Doctor.