The most common side effects with COVID-19 vaccine Janssen in the clinical trials were pain at the injection site, headache, tiredness, muscle pain and nausea. They were mild or moderate and resolved within 1 or 2 days after vaccination. They affected more than 1 in 10 people.
Rare side effects (that occurred in fewer than 1 in 1,000 people) are hypersensitivity (allergy) and itchy rash. Thrombosis (formation of blood clots in the blood vessels) in combination with thrombocytopenia (low levels of blood platelets) occurred in fewer than 1 in 10,000 people who received the vaccine in the trial.
Allergic reactions, including one case of anaphylaxis (severe allergic reaction), have occurred in people receiving the vaccine. As for all vaccines, COVID-19 Vaccine Janssen should be given under close supervision with appropriate medical treatment available.
Common side effects following vaccination with Janssen COVID-19 are mild.
More serious side effects are possible but rare.