The AstraZeneca and J&J vaccines share the same technology. It could explain why both have possible links to rare blood clots.

johnson & johnson vaccine
Nurse Elizabeth Johnson administers a COVID-19 vaccine to Melissa Mendez in Reading, Pennsylvania.

  • AstraZeneca’s coronavirus vaccine may be linked to a type of rare blood clot in the brain.
  • The same type of clot might also be associated with J&J’s shot, but regulators aren’t sure yet.
  • Experts wonder whether the clotting issues are related, since both shots use the same technology.
  • See more stories on Insider’s business page.

When coronavirus vaccines were rolled out to the public, regulators knew they would need to watch out for extremely rare reactions. Although clinical trials had shown the shots to be safe among tens of thousands of people, the world was about to vaccinate tens of millions.

Their vigilance paid off earlier this month when European regulators announced that rare blood clots might be an uncommon side effect of AstraZeneca’s vaccine. Then on Tuesday, US regulators recommended a pause in the distribution of Johnson & Johnson’s vaccine due to six reports of the same type of clot among women who’d received that shot.

AstraZeneca’s and J&J’s vaccines share a platform: Both are viral-vector vaccines, which introduce a coronavirus gene into the body using a genetically engineered common-cold virus, called an adenovirus. Some medical experts are now wondering whether that technology itself could be linked to clotting.

“Why are we seeing these few cases for J&J and AstraZeneca? We don’t know. It just makes sense – hey, maybe, it’s how the vector is introduced, because that’s the biggest difference,” Dr. Vivek Cherian, a hospitalist at the University of Maryland St. Joseph Medical Center, told Insider.

Regulators haven’t discovered the same clotting issues with the Pfizer and Moderna vaccines, which rely on a different technology: mRNA that spurs the body to produce one of the coronavirus’ signature proteins, thereby stimulating an immune response.

But scientists are still trying to figure out why only certain people – mostly young women so far – develop these rare clots, and whether all vector vaccines might trigger the same reaction.

A reaction to the adenovirus?

The particular blood clot in question, central venous sinus thrombosis (CVST), forms in the brain – so it can lead to headaches or stroke. In an average year, this condition occurs in about five people out of every million.

By early April, European medical officials had identified 169 CVST cases out of more than 34 million people in the European Union who’d received AstraZeneca’s shot. That’s still just five cases per million shots – about the rate you’d see in a normal population – so researchers weren’t sure whether the clots were caused by the vaccine.

But after reports of CVST among women who’d received the Johnson & Johnson’s vaccine, a link started to seem more probable.

COVID vaccine
A patient receives an injection of the Oxford/AstraZeneca COVID-19 vaccine.

Regulators also noticed a distinct pattern among all the vaccine-related cases: In addition to CVST, the patients had low levels of platelets – colorless blood cells that help clots form.

“This type of a combination of low platelets and blood clots has been very rarely seen in the past in other situations as an autoimmune phenomenon, but it’s very, very rare,” Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said in a Tuesday briefing.

Before the vaccines were authorized, this combination was primarily seen in association with the blood-thinning drug heparin. In rare cases, people taking the medication develop antibodies that bind to a specific platelet, which can make them more susceptible to clots.

In a study of 11 people who developed clots after receiving AstraZeneca’s vaccine, they all tested positive for antibodies against that same platelet.

“Whether there’s some kind of a reactive mechanism based on the adenovirus, and whether that somehow activates these platelets – that’s what they’re trying to look into,” Peter Gulick, an associate professor of medicine at Michigan State University, told Insider, referring to US and European regulators.

Other vector vaccines may not necessarily have the same blood-clot links

johnson & johnson vaccine
A vial of Johnson & Johnson’s shot.

Before AstraZeneca’s and J&J’s shots, only a couple viral vector vaccines had ever been authorized in humans: In 2017, China approved an Ebola vaccine that uses an adenovirus, but that shot was only authorized for emergency use, so relatively few people have ever received it. The US and EU approved another viral vector vaccine for Ebola in 2019, but the shot hasn’t been widely administered, either.

For that reason, it’s hard to know whether blood clots may be a rare issue associated with vector vaccines in general, or if the reaction is just related to the specific adenoviruses used in AstraZeneca’s and J&J’s shots.

It’s also possible, of course, that these clots aren’t associated with vaccines at all.

“I don’t think [clotting is] something that we automatically expect with a vector vaccine,” Namandj√© Bumpus, director of the pharmacology and molecular sciences department at Johns Hopkins Medicine, told Insider.

Adenoviruses are usually harmless, Bumpus added: They’re disabled before they’re injected so that they won’t replicate inside the body. They’re also engineered to resemble common, naturally occurring viruses, which on their own don’t cause blood clots.

But the adenoviruses used in vaccines can’t be too common either, because then anyone who’d previously been exposed to them would fight them off before they could trigger an immune response. For that reason, AstraZeneca’s shot uses an adenovirus strain only found in chimpanzees. J&J’s shot, meanwhile, uses a modified human adenovirus that’s not easily recognized by the immune system.

It’s possible, Gulick said, that one particular adenovirus might cause blood clots while another might not. The vaccine dose could matter as well: A 2007 study found that high doses of adenoviral vectors triggered low platelet counts in mice. But that reaction usually occurred within 24 hours after the injection, and people who’ve developed CVST after their AstraZeneca and J&J shots usually did so within two weeks.

This suggests the condition wasn’t triggered by the body’s innate immune response (the one that leads to normal vaccine side effects like fatigue or muscle aches), but instead by the adaptive immune response – the one responsible for churning out antibodies.

It’s too soon to say whether the clots are specific to young women

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A vaccinator administers the AstraZeneca vaccine in Chester, England, on February 15, 2021.

Most of the CVST cases following AstraZeneca’s shot occurred in women under 60, while all six J&J cases were reported in women between 18 and 48.

Cherian noted that young women have higher levels of estrogen, which makes them more likely to have strong immune responses in general. Gulick, meanwhile, pointed out that women have more T-cell receptors, which can also prompt the immune system to react aggressively to foreign invaders.

“My guess is it lies somewhere in how our immune system is responding in a very, very select set of individuals to that vaccine,” Cherian said.

But Bumpus cautioned against associating the clots with any particular group yet.

“It’s just such a rare event in such a small group,” she said. “Even though it’s a bit tempting to think that it’s specific to a subgroup, we have to be unbiased a little bit and just look at the data.”

Ultimately, she added, it could take years of research to determine why some people developed clots after either shot.

“There are many medicines that we take safely and confidently, that we still all the time – even after decades of use – are learning more and more about their mechanisms and their impact on cells,” Bumpus said. “It’s just with these [vaccines], it’s all unfolding in real time in front of our eyes.”

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What is a vector file? How to identify a vector file, and which apps you can use to view or edit them

Vector files usually come in just four different types.

  • A vector graphics file is an image that can be made infinitely large or small without losing quality.
  • Common vector file types include .AI (Adobe Illustrator), .EPS (Encapsulated Postscript), and .SVG (Scalable Vector Graphics).
  • You’ll need a compatible app to edit a vector file, but you can view them with most image programs or web browsers.
  • Visit Insider’s Tech Reference library for more stories.

In general, you see two types of images on your computer: Raster graphics and vector graphics. Rasters are most common, but vectors play a critical role in graphic design and website building.

But what is a vector? And how can you quickly identify a vector file?

Here’s what you should know.

What is a vector file?

Again, there are generally two types of images you’ll see online and in apps, rasters (also known as bitmaps) and vectors.

The distinction between them can seem complicated, but is actually quite simple. Raster graphics are made of a grid of pixels, each one of which is assigned a precise color. Vectors, on the other hand, are built from mathematically defined shapes like lines and curves.

This means that vector graphics can be infinitely resized without losing any sharpness or color quality, which is great for projects that need high quality images.

vector vs raster
Vectors and rasters might look the same when small, but rasters will lose quality when they’re scaled up.

But how can you quickly identify a vector file? Most vectors come in just a few different file types, making them easy to pick out.

Common types of vector files

In the same way that there are a variety of raster file types (.JPG, .PNG, etc.), there are a number of vector file formats, each used for a different application. Here are the most common vector files in use today:

How to open a vector file

What you need to open a vector graphics file depends on your goal. Here are your options:

  • If you want to view or print a vector graphics file, you can probably open it in most graphics programs, even if they’re designed mainly for raster images. Adobe Photoshop, for example, can open AI, EPS, PDF and SVG files, though the image is opened as a raster at a fixed resolution. You just can’t edit the vector and keep it as a vector.
  • You can also view and print (but not edit) most vector graphics files in a web browser – just drag and drop the file into your browser to see it.
  • If you want to edit a vector graphics file while maintaining its scalable, resolution-independent vector characteristics, you need to open it in a suitable vector graphics application, like Adobe Illustrator. If you don’t want to use Illustrator, you can also check out CorelDRAW (the second most popular application after Illustrator), or the free and open-source app Inkscape.

What is aspect ratio? Here’s why the measurement ratio of your screen or image mattersWhat is a cloud application? Here’s everything you need to know about the internet-based softwareA beginner’s guide to graphics cards and how they help power your computer’s imagesWhat is an SD card? Here’s what you need to know about the small memory cards for electronic devices

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