The most common side effect is soreness at the injection site and headache, with most side effects lasting less than 48 hours.
Some clinical trial participants reported arm soreness, fatigue, chills, fever, or headaches that lasted a day or two, most often after the second shot. But that reaction is typically a sign that the vaccine is working – triggering the immune response (or inflammation) indicating your body recognizes this never-before-seen pathogen and is mounting a protective response against it.
The clinical trials will continue to monitor patients for side effects long after patients are vaccinated. The state of Texas will use the Vaccine Adverse Event Reporting System (VAERS), a national system co-managed by the CDC and FDA, to track vaccine safety and side effects. Texas will also employ an app called V-safe, which sends vaccine recipients text messages and check-in emails to keep tabs on their health, as well as remind them when it’s time to get their second shot.
On April 13, 2021, the FDA, “out of an abundance of caution,” decided to pause distribution of the J&J vaccine after a small number of women between the ages of 18 and 48 experienced blood clots within 13 days of vaccination. Scientists at the FDA and CDC reviewed safety data and on April 23 recommended that J&J vaccinations resume, stating the vaccine’s known and potential benefits far outweigh its potential risks. Women younger than 50 should be aware of the rare but increased risk, the CDC said, and that there are other COVID-19 vaccine options available.
It’s important to keep in mind that these blood clots were extremely rare, so no additional testing is recommended if you received the J&J vaccine and are not experiencing any symptoms. Continue to monitor for side effects for three weeks post-vaccination. After that time, the risk of an adverse reaction is very unlikely.
If you received the J&J vaccine within that time frame and are experiencing new symptoms – very severe headaches, leg pain, or shortness of breath – please contact your physician for an evaluation and let them know you recently received the J&J vaccine.
The CDC and FDA will continue to monitor the safety of all COVID-19 vaccines.