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These Side Effects Are Much More Likely After Your Second Shot, CDC Says

If you’ve been concerned about COVID vaccine side effects, The Centers for Disease Control and Prevention (CDC) has some reassuring news for you: after tracking the first several million doses, they’ve determined that “Health care providers and vaccine recipients can be reassured about the safety of Pfizer BioNTech and Moderna COVID-19 vaccines.” However, they also found that there are some minor side effects and two of these are much more likely to occur after your second shot: fever and chills. Read on for more on the CDC's insights, and to learn which rare vaccine side effects mean you shouldn't get shot two, If You Have These Vaccine Side Effects, Don't Get Another Shot, CDC Says.

In just a few short months, the CDC has collected a tremendous amount of data on the COVID vaccines’ safety. In fact, they say that safety monitoring for these vaccines has been “the most intense and comprehensive in U.S. history.” Using the Vaccine Adverse Event Reporting System (VAERS), a spontaneous reporting system, and v-safe, an active surveillance system in which patients can self-report side effects via an app, they’ve reviewed the administration of nearly 14 million doses over the course of a single month.

While the vast majority of vaccine recipients reported no side effects at all (the CDC’s systems recorded a total of 6,994 adverse effects), they determined that those found in the wild mirrored data from clinical trials. “Injection site pain, fatigue, headache, and myalgia were most frequently reported, with a higher frequency after the second dose in comparable age groups,” the report concludes.

While fever and chills were not among the most commonly reported symptoms, they were notable in that they appeared far more frequently after the second dose of the vaccine. “Enrollees reported more reactions on the day after vaccination than on any other day. For the Pfizer-BioNTech vaccine, reactions were more frequent after the second dose than the first; the reported rate of fever and chills was more than four times higher after the second dose than after the first,” the CDC reports.

Doctors have explained that certain symptoms are more common after a second vaccine dose because the immune system already recognizes the supposed “threat” from the first dose of the vaccine. "When the body's immune system sees [the vaccine] a second time, there are more cells and there's a more intense immune response, resulting in those side effects,” Bill Moss, MD, a pediatrician and professor of infectious disease epidemiology at the Johns Hopkins Bloomberg School of Public Health recently told NBC News. For this reason, side effects from the COVID vaccine are considered a sign that the vaccine is working. Still on the fence about getting vaccinated? Read on for expert insights on the benefits of the vaccine, and for more on vaccine side effects, Dr. Fauci Says These 2 Side Effects Mean Your COVID Vaccine Is Working.

No corners were cut in the process of vaccine development, experts say.

According to White House COVID advisor Anthony Fauci, MD, fears surrounding the speed of the vaccines’ development are fair but unfounded. “The speed is really a reflection of the scientific advances that have allowed us to do things in a matter of months that would have formerly taken years. And that's the reason why we have a vaccine now in less than one year from the time the virus was identified. That isn't reckless speed; that's sufficient speed based on scientific advances,” he recently told NPR. And for the latest COVID news delivered straight to your inbox, sign up for our daily newsletter.

Vaccines are “the endgame of this pandemic.”

In the same interview, Fauci said that he views the vaccine rollout as “the endgame of this pandemic,” a tool uniquely poised to bring the virus to its knees. But he also expressed concern over vaccine hesitancy, which he suggested was a major hurdle in our return to safety.

“It would be terrible to have a vaccine, which is extraordinarily efficacious—ratio is 94 percent to 95 percent efficacious in preventing clinical disease—it would be terrible, with a tool as good as that, if people don't utilize that tool,” he said. And for more essential vaccine news, check out The Pfizer CEO Says This Is How Often You'll Need a COVID Vaccine.

The benefits of getting vaccinated are being “undersold.”

According to Aaron Richterman, MD, MPH, an Infectious Disease Fellow at Penn Medicine, scientists and doctors may be underselling the benefits of the vaccines out of an abundance of caution, but the data supporting their efficacy speak volumes.

"I think the first important thing to know is that we have gold standard, A-plus evidence, our best kind of evidence that the vaccines, the mRNA vaccines Moderna and Pfizer that are becoming available are among the very best vaccines we've ever tested," Richterman told ABC News. "Getting this vaccine is going to be the ticket to gather with your loved ones, to work safely, to get out and get life back to normal again," he added.

There are valid reasons to ask questions, but the data supports vaccination.

Eugenia South, MD, MS, an assistant professor of emergency medicine at the Hospital of the University of Pennsylvania, shared her own complex path from vaccine hesitancy to endorsement with NBC News. As a Black doctor, she weighed the “centuries of structural racism” that contributed to her own medical mistrust against the hard evidence of the vaccines’ efficacy. She ultimately made her decision to get the vaccine after combing through Pfizer’s trial data.

“The graph from that study showing the continued rise of COVID-19 infection in the placebo group compared to the near complete drop-off in those who received the vaccine will forever be imprinted on my mind. In addition to being a physician, I am a scientist. And while the historical examples of experimentation on Black bodies in the name of science are too numerous to count, and concerns about racism and bias in research persist, I still trust rigorous science,” wrote South. And when you're ready to start planning your vaccination, You'll Be Able to Get Vaccinated at Any Walgreens by This Date.