Very common side effects
Very common side effects may affect more than 1 in 10 people.
- feeling tired
- pain in the arm where you had the vaccine injection
- muscle pain
Common side effects
Common side effects may affect up to 1 in 10 people.
- redness or swelling where you had the injection
- joint pain
- fever (temperature of 38 degrees Celsius or above)
Uncommon side effects
Uncommon side effects may affect up to 1 in 100 people.
- feeling weak or generally unwell
- back pain
- muscle weakness
- pain in the limbs
- pain in the throat
- a rash
- excessive sweating
- a tremor
- an unusual feeling in the skin, such as tingling or a crawling feeling (paraesthesia)
Rare side effects
Rare side effects may affect up to 1 in 1,000 people.
- allergic reaction or hives
- decreased feeling or sensitivity, especially in the skin (hypoesthesia)
- swollen lymph glands
- ringing in the ears (tinnitus)
- blood clots in the deep veins – such as deep vein thrombosis and pulmonary embolisms
Blood clots in deep veins are more likely in people who have pre-existing risk factors for these conditions.
Very rare side effects
Very rare side effects may affect up to 1 in 10,000 people.
- very unusual blood clots with low platelets
- Guillain-Barré syndrome (GBS)
Very unusual blood clots with low platelets
Very rarely, 1 in 300,000 people may develop very unusual blood clots with low platelets. 1 in 10 of these people may die. The risk of this very rare condition is higher in younger people.
Talk to your GP, doctor or the person giving you your vaccination about the risks and benefits of getting this vaccine.
Most people who got this very rare side effect got it within 14 days of getting the Janssen vaccine.
Symptoms of very rare blood clots
Get urgent medical help and mention your recent vaccination if you:
- are breathless
- have pain in the chest or stomach
- have swelling or coldness in a leg
- get a severe or worsening headache (particularly 3 or more days after the vaccine)
- have blurred vision
- feel confused
- have seizures
- have persistent bleeding under the skin where there was no previous injury
- have many small bruises, reddish or purplish spots, or blood blisters under the skin
Guillain-Barré syndrome (GBS)
GBS is a rare and serious condition that affects the nerves. Symptoms can range from mild weakness to severe paralysis (being unable to move a part of your body). Most people eventually fully recover even from the most severe symptoms. Some may continue to experience weakness.
Getting GBS after having the Janssen vaccine is very rare. Only a small number of people have reported getting the condition after being vaccinated.
You should know the symptoms to look out for in the weeks after being vaccinated.
Get urgent medical help if you develop:
- double vision or difficulty moving your eyes
- difficulty swallowing, speaking, or chewing
- co-ordination problems and unsteadiness
- difficulty walking
- tingling sensations in your hands and feet
- weakness in your arms, legs, chest or face
- problems with bladder control and bowel movements
Extremely rare side effects
We do not know yet how many people are affected by extremely rare side effects. There is not enough data available at this time.
- severe allergic reaction (anaphylaxis)
- capillary leak syndrome
- immune thrombocytopenia
- transverse myelitis (inflammation of the spinal cord)
- cutaneous small vessel vasculitis (inflammation of blood vessels in the skin)
Capillary leak syndrome
A very small number of people have experienced capillary leak syndrome after getting the Janssen vaccine.
Capillary leak syndrome is a very rare but serious condition. It can sometimes be fatal. Do not get the Janssen vaccine if you have previously had capillary leak syndrome.
Get urgent medical attention if you have had a Janssen vaccine in the past few days and you notice:
- rapid swelling of your arms or legs
- sudden weight gain
You may also feel faint due to low blood pressure.
Capillary leak syndrome is usually reported within 4 days of getting the Janssen vaccine. Watch out for these symptoms in the days after your vaccination.
Extremely rarely, very low levels of blood platelets (immune thrombocytopenia) may happen. This can cause bleeding and can sometimes be fatal. It usually happens within 4 weeks of getting the Janssen vaccine. Some cases have been seen in people who have previously had immune thrombocytopenia.
Cutaneous small vessel vasculitis
A very small number of cases of cutaneous small vessel vasculitis (inflammation of blood vessels in the skin) have occurred in people after this vaccine. In most cases, symptoms get better with supportive care.