What are the side effects of the Johnson & Johnson vaccine?

side effects Johnson & Johnson vaccine, blood clot
© Stanislav Sukhin

Here, we discuss some of the common misconceptions about side effects of the Johnson & Johnson COVID vaccine

The Johnson & Johnson vaccine can create an efficacy of 66% in one dose, while mRNA vaccines like Pfizer need two doses to create strong enough protection. The vaccine can be kept at a standard fridge temperature for three months, then at -20°C for two years. This means that an existing cold supply chain can transport the vaccines.

The Johnson & Johnson vaccine is different to all others, as it only needs one dose to protect against COVID hospitalisation and death. It currently has Emergency Use Approval in the US.

However, the latest fears about blood clot risks may have damaged the perception of how safe this vaccine is. Here, we look at the science behind any existing side effects for the Johnson & Johnson vaccine.

1. What are the common side effects for Johnson & Johnson?

The general impact on the arm and body are the same as with other vaccines. With UK vaccination data on Pfizer and AstraZeneca, it seems that one fourth of people are getting side effects. Within that group, scientists found that if a person had previously had COVID-19, they would likely have stronger side effects. 

Usually, a fever or headache means that the immune system is accepting the new defences against the virus. The side effects of the Johnson & Johnson vaccine are a good sign.

In the arm:

  • Pain
  • Redness
  • Swelling/itching

In the body:

  • Fever
  • Chills
  • Rash
  • Nausea/vomiting
  • Headache/dizziness
  • Arthralgia
  • General itching
  • And fatigue

2. Will the Johnson & Johnson vaccine give me blood clots?

It is highly unlikely, but possible. 

There are currently 17 cases of blood clot out of 8 million doses given.

That’s a 0.002125% chance of experiencing a major blood clot, after taking the one-dose vaccine.

Though the US temporarily suspended use, the vaccine is back with a warning attached. However, Denmark decided to permanently suspend the vaccine.

It is more likely that birth control creates a life-threatening blood clot.

The side effects are happening in women between 18-48 years old, with symptoms coming six to 13 days after their vaccination. Those with low levels of platelets are more likely to be at risk.

The FDA ask that: “People who have received the J&J vaccine who develop severe headache, abdominal pain, leg pain, or shortness of breath within three weeks after vaccination should contact their health care provider.”

The full list of blood clot symptoms are:

  • shortness of breath
  • chest pain
  • leg swelling
  • persistent abdominal pain
  • neurological symptoms (including severe or persistent headaches or blurred vision)
  • easy bruising
  • tiny blood spots under the skin beyond the site of injection of the vaccine

3. Can Johnson & Johnson side effects make me infertile?


The Johnson & Johnson vaccine is not an mRNA vaccine, like Pfizer or Moderna. Both Pfizer and Moderna faced the suspicion that awaits a new type of vaccine – with people wondering if their DNA would be permanently changed, or if they would be able to create children after the vaccine.

In December, 2020, a German doctor and anti-vaccine supporter, begun to create a false link between syncytin-1 (an ingredient in the vaccine) and the human placenta. His argument was that they share genetic makeups, meaning that the vaccine could then attack the human placenta and make the body unable to carry a baby.

But this is impossible. The antibodies created after the vaccine are specifically coded to fight the virus and protect the human body. If the antibodies were to suddenly turn on the human body, this would have been spotted at Phase One, Phase Two and especially the huge Phase Three stage of clinical trials for every single COVID-19 vaccine.

When it comes to Johnson & Johnson, the ENSEMBLE study had participants that later went on to become safely pregnant.

So far, more than 30,000 pregnant women have taken the Pfizer and AstraZeneca vaccines. They reported no adverse side effects to the Center for Disease Control. Real-world Johnson & Johnson data is going to become available to the CDC soon.

4. Can I have an allergic reaction to the vaccine?


A severe allergic reaction would usually occur within a few minutes to one hour after
getting a dose of the Johnson & Johnson vaccine.

What are the symptoms of a severe allergic reaction?

  • Difficulty breathing;
  • Swelling of your face and throat;
  • A fast heartbeat;
  • A bad rash all over your body;
  • And dizziness and weakness.

Check if you have any problems with these ingredients:

  • Recombinant;
  • Replication-incompetent adenovirus type 26 expressing the SARS-CoV-2 spike protein;
  • Citric acid monohydrate;
  • Trisodium citrate dihydrate;
  • Ethanol;
  • 2-hydroxypropyl-β-cyclodextrin (HBCD);
  • And polysorbate-80, sodium chloride.

If you are not sure about a reaction you are having, please contact a healthcare professional. 


  1. Well I got the J&j vaccine on April 2 and on April 23rd I was diagnosed with blood clot in my leg. How many other people got blood clots that weren’t the cerebral kind which are the only ones being talked about. I’m sure there are others then just me.


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