Johnson & Johnson’s Janssen COVID-19 Vaccine Overview and Safety

Updated June 23, 2021

General Information

Possible Side Effects

These side effects happen within a day or two of getting the vaccine. They are normal signs that your body is building protection and should go away within a few days.

Fainting After Vaccination

Fainting (syncope) and other events that may be related to anxiety like rapid breathing, low blood pressure, numbness, or tingling can happen after getting any vaccine. Although uncommon, these events are not unexpected, and they are generally not serious.

According to information from the Vaccine Adverse Event Reporting System (VAERS), there were 653 reports of fainting events (fainting and near-fainting) among nearly 8 million doses of J&J/Janssen COVID-19 Vaccine administered in the United States in March and April 2021. This translates to a rate of about 8 fainting events for every 100,000 doses of the J&J/Janssen COVID-19 Vaccine given. These events occurred during the recommended 15-minute wait after vaccination. It’s not clear at this time whether these events were associated with the vaccine or with anxiety, possibly related to preexisting concerns some people who chose to get the one-dose J&J/Janssen COVID-19 Vaccine may have about needles or shots.

By comparison, the rate of fainting after flu vaccination in 2019–2020 was 0.05 per 100,000 doses.

Safety Data Summary

• In clinical trials, side effects were common within 7 days of getting vaccinated and were mostly mild. Some people had side effects that affected their ability to do daily activities.
• Side effects were more common in people 18–59 years old compared to people 60 years and older.
• There is a plausible causal relationship between J&J/Janssen COVID-19 Vaccine and a rare and serious adverse event—blood clots with low platelets (thrombosis with thrombocytopenia syndrome, or TTS).

• • It occurs at a rate of about 7 per 1 million vaccinated women between 18 and 49 years old.
  • For women 50 years and older and men of all ages, this adverse event is even more rare.

• Find the latest updates on J&J/Janssen COVID-19 Vaccine and blood clots with low platelets.

• CDC will continue to provide updates as we learn more about the safety of the J&J/Janssen COVID-19 Vaccine in real-world conditions.

How Well the Vaccine Works

• The J&J/Janssen COVID-19 Vaccine was 66.3% effective in clinical trials (efficacy) at preventing laboratory-confirmed COVID-19 infection in people who received the vaccine and had no evidence of being previously infected. People had the most protection 2 weeks after getting vaccinated.
• In the clinical trials, the vaccine had high efficacy at preventing hospitalization and death in people who did get sick. No one who got COVID-19 at least 4 weeks after receiving the J&J/Janssen COVID-19 Vaccine had to be hospitalized.
• CDC will continue to provide updates as we learn more about how well the J&J/Janssen COVID-19 Vaccine works in real-world conditions.

Clinical Trial Demographic Information

Clinical trials for the J&J/Janssen COVID-19 Vaccine included people from the following racial, ethnic, age, and sex categories:

Race:

• 62% White
• 17% Black or African American
• 8% American Indian or Alaska Native
• 5% multiple races
• 4% Asian
• 0.3% Native Hawaiian or Other Pacific Islander

Ethnicity:

• 45% Hispanic or Latino
• 52% not Hispanic or Latino
• 3% unknown

Sex:

• 56% male
• 45% female
• <0.1% undifferentiated or unknown sex

Age breakdown:

• 67% 18–59 years
• 34% 60 years and older
  • 20% 65 years and older
  • 4% 75 years and older

Forty (40.8%) of people who participated in the clinical trials had at least one condition that put them at risk of severe illness from COVID-19. The most frequent underlying medical conditions among participants were obesity (28.7%), high blood pressure (10.2%), type 2 diabetes (7.3%), and HIV infection (2.7%).