It’s too soon to know what specifically caused the blood clots — that’s the biggest reason the vaccine administration was paused

An illustration of the inside of a red blood vessel with a clump of red blood cells traveling through it.
An illustration of the inside of a red blood vessel with a clump of red blood cells traveling through it.
Image by Mecder

The CDC and FDA jointly recommended pausing administration of the Johnson & Johnson Covid-19 vaccine Tuesday April 13, sending a lot of people into a tailspin of questions about what the suspension means and whether the vaccine is safe. Here’s an explainer that answers as many of those questions as carefully as is currently possible — no doubt more answers will come every day.

What happened?

On April 13, the FDA and CDC jointly announced a recommendation that administration of the Johnson & Johnson Covid-19 vaccine pause to allow investigation of a possible safety concern. Out of 6.8 million doses of the…


A long history of dismissing women’s experiences in medicine may be limiting reported side effects in clinical trials

a Black woman wearing a blue sleeveless top receives a bandaid after receiving a vaccination from a white-appearing woman whose face is away from the camera
a Black woman wearing a blue sleeveless top receives a bandaid after receiving a vaccination from a white-appearing woman whose face is away from the camera
Photo by CDC on Unsplash

Vaccine trials include tens of thousands of people in phase 3 to ensure that even rare side effects are more likely to be detected. But once the vaccine is authorized and millions of people have begun receiving it, sometimes researchers learn about other even rarer side effects not captured in the trials. But scientists could also miss a side effect if they simply don’t ask about it — or don’t record it when participants report it.

That may be why it’s taken months after the vaccines were authorized by the FDA to explore whether changes in menstruation might be a…


Photo by Helena Lopes on Unsplash

Risk assessment is hard. Nearly every situation has a range of different variables that affect risk, and only some of these variables can be quantified. Others we have to estimate, and in the human brain, emotions inevitably get tangled up in the process of trying to make those estimations and come to an overall idea of how risky something is or isn’t.

“This is why medical doctors and people in public health train for years to help people understand the public health landscape and marry public health with their own individual conditions and risk,” Lucy McBride, MD, an internist in…


Photo: Alex Mecl/Unsplash

For the most part, getting a Covid-19 vaccination shouldn’t change any of your typical health, fitness, or wellness routines, or at least not for more than a day or two. Still, it’s reasonable to have questions about whether you should hold off on certain things, such as working out, drinking alcohol, or taking certain medications. Below are some of the common questions people have about what they should or shouldn’t do after vaccination related to their own health. …


Your unvaccinated child is nothing like a vaccinated grandma.

Photo by Luca Baini on Unsplash

We all have mental lists of the things we’ve missed most during the pandemic, and we’re eager to get back to some semblance of normalcy that seems promised by the vaccines. While the CDC has affirmed that vaccinated adults can safely get together, parents still have to consider what gatherings and travel mean without the ability to vaccinate their children for many months to come. It’s been suggested that children’s mostly mild infections and low susceptibility to severe outcomes eases this decision-making because parents can think of their unvaccinated child’s risk of the worst outcomes — hospitalization and death —…


Plus, the most important way to prevent more variants from emerging

Image: Andriy Onufriyenko/Getty Images

Although the word “mutation” often conjures frightening associations, such as three-headed fish or The Andromeda Strain, in reality, mutations are simply changes that arise in DNA or RNA. Reproduction is one opportunity for these changes to emerge, creating the starting material for evolution, including in viruses. In this way, as researcher Nathan D. Grubaugh and colleagues wrote back in March 2020, mutations are just “a humdrum aspect of life for an RNA virus.”

But recent reporting about mutated variants of the SARS-CoV-2 virus has understandably caused some anxiety. …


As a reporter specializing in vaccines, I knew it was possible — but never thought it would happen quite like this

Photo: Daniel Schludi/Unsplash

Tomorrow, it will have been exactly one year since the first Moderna trial began for the groundbreaking mRNA Covid-19 vaccine. Having covered vaccines as a journalist for a decade, never in my wildest dreams did I imagine that less than a year later, I would have two doses of that vaccine in my arm, that it would reduce my risk of catching the coronavirus by 95%, that it would eliminate my risk of death from the disease despite multiple risk factors, and that the worst I’d suffer for it would be a sore arm for a week or so. As…


Reactions frequently occur after vaccines while the immune system is doing its thing

Photo: Steven Cornfield/Unsplash

About five days after I got my Moderna vaccine, I found myself scratching the place where I’d gotten it. At first it was automatic, like scratching any itch, but soon I realized it was really itchy — and big and warm and red. I knew there could be injection site reactions, but with all my past vaccines, it had only been red or swollen at the injection site for a day or two after the shot. This was a week later, which seemed weird.


It’s better not to gather, but here’s how to lower the risk if you do

Photo: Kira auf der Heide/Unsplash

As we head into peak holiday season, the U.S. death toll from Covid-19 has just surpassed 300,000 deaths. The nation is now averaging a daily death toll equivalent to the 9/11 terrorist attacks — every day — with no signs of slowing down. It’s no surprise, then, that the Centers for Disease Control and Prevention (CDC) advises that the “safest way to celebrate winter holidays is to celebrate at home with the people who live with you.” They even provide some great ideas on the safest way to celebrate apart from one another.

As we saw with Thanksgiving, however, millions…


Photo illustration sources: Getty Images/Tetra Images and Andriy Onufriyenko

Clear guidance on everything you want to know about the vaccine (and then some)

This FAQ will be frequently updated and added to as the vaccine process continues —the most recent update was on February 10, 2021. If you have a question that isn’t answered here, please let us know by commenting on this story, and we’ll consider it for our next update.

Exactly 272 days after the World Health Organization declared Covid-19 a global pandemic, 90-year-old Margaret Keenan and 81-year-old William Shakespeare in the United Kingdom became the first two people in the world to receive a thoroughly tested Covid-19 vaccine. (Yes, China and Russia began vaccinating people much earlier, but it’s not…

Tara Haelle

Tara Haelle is a science journalist, public speaker, and author of Vaccination Investigation and The Informed Parent. Follow her at @tarahaelle.

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