Feeling fatigued or feverish after your COVID-19 vaccine? Here's why the CDC wants to know

Abby Haglage
·5 min read

Thus far, the data that's been gathered on the COVID-19 vaccines suggests that the majority of reactions to the shots are mild — including things like headache, fever, fatigue and nausea. But with over 38 million people in the U.S. now fully vaccinated, the Centers for Disease Control and Prevention is continuing to gather information about how those who get the vaccines are responding, doing it through an — as of yet little-known — app called V-safe.

The CDC describes V-safe as a "smartphone-based tool that uses text messaging and web surveys to provide personalized health check-ins after you receive a COVID-19 vaccine." The program asks you to report any side effects you experience after the vaccine and, depending on their severity, may prompt someone from the CDC to reach out for more information. This week, the app received criticism for the fact that it's available only on smartphones, excluding the millions of people in the U.S. who do not have one.

The CDC has created a text-messaging based app called V-Safe to record side effects after getting the COVID-19 vaccine. Here's why that is important. (Photo: Getty Images)
The CDC has created a text-messaging-based app called V-Safe to record side effects after getting the COVID-19 vaccine. Here's why that is important. (Photo: Getty Images)

But for the vast majority who do, says Dr. Carolyn B. Bridges, associate director for adult immunization at the Immunization Action Coalition, it can be an extremely helpful resource. Here's what you need to know.

Anyone vaccinated can sign up for V-safe, and your vaccination center should have information about it

Bridges says vaccine distribution centers should provide info about V-safe. "When you go get your vaccine, they should be giving you a handout with a QR code on there, which you can use to sign up," she says. "They'll send you questions about the kind of side effects that you're having for a period of time after you get your vaccine ... and if you have a more unusual or severe something to report, then you may get a follow-up call." For those who do not receive a handout, the CDC has directions about the registration process on its website.

The info gathered on V-safe is supplemental to VAERS, the Vaccine Adverse Event Reporting System

The CDC has long tracked severe reactions to vaccines through VAERS, the Vaccine Adverse Event Reporting System, which requires clinicians to record any concerning clinical reactions. Bridges says that V-safe is not a replacement, but merely an additional way to track side effects through self-reporting. "These vaccine trials have all been large, 40,000 people or so, but that may not pick up something that occurs in one in a million," she says. "So while VAERS is ongoing, V-safe is supplemental and involves you getting a text message you respond to."

Since the U.S. vaccination program moved at unprecedented speed, churning out multiple vaccines in less than a year, V-safe helps fill in the gaps, and Bridges says it may even make some feel better about their choice to get one. "I think it's important for people to participate in V-safe if they want to contribute," she says. "I think it will be important for people who maybe were not as comfortable with the vaccination at the beginning, just to give them a little more control and more information."

Nearly 4 million Americans have begun reporting on V-safe, recording side effects like headache and fatigue

During a meeting on March 1, Dr. Tom Shimabukuro, deputy director of the Immunization Safety Office at the CDC, shared the first data about V-safe, revealing that 3.8 million people had begun using the app by Feb. 16. The number represented just a small fraction of the 55 million individuals who had received one or more doses of the Pfizer or Moderna vaccines (the Johnson & Johnson vaccine was not yet available) by that time, but his publicly available presentation shows valuable insight gained from data.

For example, much like volunteers in Pfizer's and Moderna's vaccination studies, those who received the vaccines reported three main symptoms after the shots: fatigue, headache and myalgia (muscle pain). These side effects were followed by other common ones including chills, nausea and fever. Reactions significantly increased after individuals got the second dose of Pfizer. (At the time, information for the second Moderna dose was not available.)

More than 16,000 individuals reported getting pregnant after their vaccination

Of all the myths circulating about the COVID-19 vaccine, the one suggesting that the vaccines may cause infertility in women seems particularly damaging. But as of mid-January, the V-safe data, according to Shimabukuro's slides, included 30,000 pregnant women, providing data that led the CDC to conclude that "adverse events observed among pregnant women in V-safe did not indicate any safety problem."

Bridges says this is one example of why V-safe is so valuable, especially given that neither Moderna's nor Pfizer's clinical trials included pregnant women. "All the pregnancies recorded, that is incredibly helpful to have that data," she says. "[There has been] misinformation and what we all want and need is real data — information that's accurate. So I think this is a really great way if people are willing to volunteer."

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