Serious side effects are rare. As with any medicine, it is possible to have a serious allergic reaction, such as not being able to breathe. This reaction is very rare but if it does happen, it is usually within in first 15 to 30 minutes after vaccination. Everyone is observed after getting a COVID-19 vaccine so that healthcare providers can treat an allergic reaction straight away.
There is a risk of a rare but serious condition involving blood clots and low platelets in people after receiving the Johnson and Johnson COVID-19 Vaccine. This risk is very low. This problem is rare and happened in about 7 per 1 million vaccinated women between 18 and 49 years old. For women 50 years and older and men of any age, this problem is even more rare. This problem has not been linked to the other two COVID-19 vaccines (Pfizer and Moderna).