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The Johnson and Johnson COVID-19 vaccine is the third COVID-19 vaccine that the Food and Drug Administration (FDA) authorized for emergency use. That means it’s been found to be both safe and effective.

It’s normal to have questions about any new vaccine, medication, or procedure. Below, we’ll address questions or concerns that you may have about the Johnson and Johnson COVID-19 vaccine.

Before we dig deeper into the Johnson and Johnson (J&J) COVID-19 vaccine, let’s review some key points:

  • The J&J COVID-19 vaccine only requires one dose instead of two.
  • This vaccine uses viral vector technology instead of mRNA.
  • Clinical trials found that this vaccine was effective at preventing both mild to moderate COVID-19 as well as severe COVID-19. They also indicated that the vaccine is effective for some COVID-19 variants.
  • The J&J COVID-19 vaccine shares common side effects with the other COVID-19 vaccines, such as injection site reactions, headache, and fatigue.
  • Although a very small number of serious blood clots have been reported following vaccination, the risk of these happening is very low.

The Centers for Disease Control and Prevention (CDC) and the FDA recommended a pause of the J&J COVID-19 vaccine on April 13, 2021. At the time of the pause, about 6.8 million doses of the vaccine had been given.

The purpose of this pause was to further investigate rare blood clots that had been reported after vaccination. It also served to inform healthcare professionals on how to identify and treat these clots, should they occur.

What are these clots?

The reported blood clots occurred in the large blood vessels of the brain or abdomen and were associated with low platelet counts. The medical term for this condition is thrombosis with thrombocytopenia syndrome (TTS).

Who got these clots?

Six instances of TTS, including one death, had been reported at the time of the pause. All of these cases involved women between ages 18 and 48 years old. Symptoms of TTS began 1 to 2 weeks after receiving the J&J COVID-19 vaccine.

At the time of writing, nine further instances of TTS have been reported, according to the FDA. Two of these additional cases were associated with deaths.

Was the pause lifted?

Yes. On April 23, 2021, the pause on the J&J COVID-19 vaccine was lifted. After thoroughly reviewing the data on the reported cases of clots developing, the CDC and the FDA concluded that the known benefits of the J&J COVID-19 vaccine outweighed its potential risks.

Should I be concerned?

TTS is a very rare side effect of the J&J COVID-19 vaccine. According to the CDC, it occurs at a rate of 7 per 1 million female individuals between the ages of 18 and 49 years. Female individuals over age 50 years and male individuals are at an even lower risk.

If you’re a person assigned female at birth and you’re under 50 years old, it’s important to be aware of the risk of these blood clots as well as their potential symptoms.

If you have reservations about receiving the J&J COVID-19 vaccine, there are other COVID-19 vaccines available that aren’t associated with this side effect. These include the Pfizer-BioNTech and Moderna vaccines.

Warning signs for complications from a COVID-19 vaccine

You may now be wondering about the warning signs of potential complications from the J&J COVID-19 vaccine. Let’s take a look at these now.

One of the potential complications of any COVID-19 vaccine is severe allergic reaction. Symptoms typically happen shortly after receiving the vaccine and can include:

Severe blood clots (TTS) are very rare, but they can also occur. The CDC recommends being on the lookout for symptoms for 3 weeks after receiving the J&J COVID-19 vaccine. Potential symptoms can include:

If you develop any of the symptoms above, seek immediate medical care.

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To authorize a vaccine for emergency use, the FDA must find that the vaccine is both safe and effective. The agency reviewed clinical trial data from over 40,000 participants as well as manufacturing information that Johnson and Johnson provided.

The FDA granted the J&J COVID-19 vaccine emergency use authorization (EUA) on February 27, 2021. It became the third COVID-19 vaccine in the United States to receive an EUA.

Additionally, both the World Health Organization (WHO) and European Medical Association (EMA) have found the J&J COVID-19 vaccine to be both safe and effective.

What are the common side effects

The phase 3 clinical trial of the J&J COVID-19 vaccine found that the most commonly reported side effects were similar to those of the other authorized COVID-19 vaccines. These side effects were more common in people under 60 years old and included:

These side effects typically happen within a day or two of getting the vaccine and will go away in a few days. They’re completely normal and a sign that your body is building an immune response.

Are there rare side effects

Some much rarer side effects were also observed during the phase 3 clinical trial. These occurred in very few people.

Out of the 21,895 individuals who received the vaccine, only 7 people had a severe adverse effect that was considered to be related to vaccination. This is about 0.03 percent of trial participants in the vaccine group. These effects included:

The investigators did note some blood clot events. For example, 11 blood clotting events were observed in the vaccine group compared with 3 in the placebo group. Most of these participants had underlying conditions that increase the risk of blood clots.

A note on vaccine severe adverse effects

Severe adverse effects from vaccination are very rare overall. In fact, contracting the coronavirus and developing the condition typically carries more risk.

For example, a 2017 review discussed the risk from the measles-mumps-rubella (MMR) vaccine compared with actually contracting the measles virus and developing measles. It found that:

  • About 2 in 1,000 cases of measles result in death. Only 397 instances of death following the MMR vaccine have ever been reported since its introduction in 1971.
  • About 1 in 1,000 people with measles will experience encephalitis. This only occurs after 1 out of 3 million MMR vaccinations.
  • A rare complication called subacute sclerosing panencephalitis happens in 8.5 out of 1 million people with measles. Between 0 and 0.7 cases per 1 million MMR vaccinations have been reported.
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The J&J COVID-19 vaccine is a viral vector vaccine. This means that it uses a virus to deliver the vaccine components. Let’s examine this in more detail.

Creating the vector

An adenovirus vector is used for the J&J COVID-19 vaccine. Normally, adenoviruses cause respiratory infections in humans.

However, this adenovirus has been modified so that it cannot replicate within cells. This means that it cannot cause illness. It simply helps to deliver the vaccine components into your cells before being broken down.

To create the vaccine, the gene for the novel coronavirus spike protein was inserted into the adenovirus’ genetic material. The spike protein is normally found on the outside of the novel coronavirus and is used to bind to host cells.

It’s important to note that the genetic material supplied by the adenovirus vector cannot change your DNA in any way. Unlike some other types of viruses, such as HIV, adenoviruses don’t have the capability of integrating into DNA.

How exactly does this work?

After the J&J COVID-19 vaccine is given, the modified adenovirus enters host cells in your body and releases its genetic material.

Your cells use the instructions in the genetic material the viral vector provides to produce spike protein, which is then transported to the cell surface.

Your immune system can see the spike protein on the cell surface and identify it as foreign. It produces an immune response, during which antibodies and immune cells that specifically recognize spike protein are made.

Should you come into contact with the novel coronavirus, your immune system will have been primed to recognize and defend against it. This can help to prevent you from developing COVID-19.

Why is it just one dose?

One of the main things that you may have heard about the J&J COVID-19 vaccine is that it requires just one dose instead of two. Why is this?

Early clinical trials tested both a one- and two-dose vaccine regimen. It was found that 90 percent of participants made robust levels of neutralizing antibodies 29 days after the first dose. Researchers found that levels of these antibodies remained stable 71 days after the first dose.

The extent and stability of this response prompted researchers to continue with the one-dose regimen in further trials. Trials to investigate a two-dose J&J COVID-19 vaccine regimen are also ongoing.

You may be wondering how exactly is the J&J COVID-19 vaccine different from the Pfizer-BioNTech and Moderna vaccines. Generally speaking, there are three major differences:

  • Doses needed. The J&J COVID-19 vaccine only requires one dose. Both the Pfizer-BioNTech and Moderna vaccines require two doses, separated by 3 weeks and 4 weeks, respectively.
  • Technology. The J&J COVID-19 vaccine uses viral vector technology. The Pfizer-BioNTech and Moderna vaccines use mRNA technology.
  • Storage. The J&J COVID-19 vaccine can be refrigerated, while the Pfizer-BioNTech and Moderna vaccines need to be kept frozen.

You may be wondering why we didn’t list differences in effectiveness. This is because the clinical trials for the three COVID-19 vaccines were:

  • carried out at different times during the pandemic
  • located in different geographic locations
  • completed using different study protocols

According to the FDA, it’s only possible to directly compare the effectiveness of the three COVID-19 vaccines with a head-to head clinical trial. Overall, all three authorized COVID-19 vaccines are effective at preventing COVID-19.

Finding a Johnson and Johnson COVID-19 vaccine

If you’d like to receive a J&J COVID-19 vaccine, follow the tips below:

  • VaccineFinder. VaccineFinder is a searchable resource to find COVID-19 vaccines near you. You can use a filter to search for locations offering the J&J COVID-19 vaccine.
  • State health hepartments. Your state’s health department may be able to help you find a J&J COVID-19 vaccine close to you. You can find your state’s health department here.
  • Your healthcare professional. Contact your healthcare professional to see if they’re offering the J&J COVID-19 vaccine.
  • Local pharmacies. Many local pharmacies are now offering COVID-19 vaccines. Talk with those in your area to see if they have the J&J COVID-19 vaccine.

When you get your vaccine, you’ll be given a COVID-19 vaccine card that details which vaccine you received as well as when and where you received it. Be sure to hang on to this card and store it in a safe place.

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The phase 3 clinical trial of the J&J COVID-19 vaccine included people from several locations across the globe. It measured the ability of the vaccine to prevent both mild to moderate COVID-19 and severe COVID-19.

The J&J COVID-19 vaccine’s effectiveness at preventing mild to moderate COVID-19 14 days or more after vaccination was:

  • Overall: 66.3 percent
  • United States: 74.4 percent
  • Brazil: 66.2 percent
  • South Africa: 52 percent

The J&J COVID-19 vaccine was also effective at preventing severe COVID-19 14 days or more after vaccination. In this case, its effectiveness was:

  • Overall: 76.3 percent
  • United States: 78 percent
  • Brazil: 81.9 percent
  • South Africa: 73.1 percent

These findings are also notable because they provide information about the vaccine’s effectiveness for viral variants. These include the B.1351 variant first seen in South Africa and the P.2 variant discovered in Brazil.

The researchers note that most viruses discovered in both Brazil and South Africa at the time of the trial were variants. As such, the trial results indicate that the J&J COVID-19 vaccine is effective for these variants.

Now let’s examine the various pros and cons of the J&J COVID-19 vaccine.


  • Safe and effective for preventing both mild to moderate and severe COVID-19.
  • Clinical trial data also indicate effectiveness for some COVID-19 variants.
  • Only one dose is required.
  • Can be refrigerated instead of frozen.


  • It shares common side effects with other COVID-19 vaccines, such as injection site reactions, aches and pains, and headache.
  • Has a very low risk of serious side effects like severe allergic reaction and serious blood clots.
  • There’s risk of contracting the coronavirus and developing COVID-19, as none of the authorized COVID-19 vaccines are 100 percent effective.
Was this helpful?

The J&J COVID-19 vaccine is the third vaccine that has been authorized for emergency use in the United States. Unlike the other authorized COVID-19 vaccines, it only requires one dose.

Clinical trial data has shown that the J&J COVID-19 vaccine is both safe and effective for preventing both mild to moderate and serious COVID-19. It’s also been found to be effective against viral variants.

Common side effects of the vaccine are injection site reactions, fatigue, and headache. Severe side effects are very rare.

If you have questions or concerns about receiving the J&J COVID-19 vaccine, be sure to discuss them with your doctor.