Safety Monitoring of the Janssen (Johnson & Johnson) COVID-19 Vaccine

United States, March-April 2021

David K. Shay, MD; Julianne Gee, MPH; John R. Su, MD, PhD; Tanya R. Myers, PhD; Paige Marquez, MSPH; Ruiling Liu, PhD; Bicheng Zhang, MS; Charles Licata, PhD; Thomas A. Clark, MD; Tom T. Shimabukuro, MD


Morbidity and Mortality Weekly Report. 2021;70(18):680-684. 

In This Article

Abstract and Introduction


On February 27, 2021, the Food and Drug Administration (FDA) issued an Emergency Use Authorization (EUA) for Janssen (Ad.26.COV2.S) COVID-19 vaccine (Janssen Biotech, Inc., a Janssen Pharmaceutical company, Johnson & Johnson).[1] The Janssen COVID-19 vaccine, the third COVID-19 vaccine authorized for use in the United States, uses a replication-incompetent human adenoviral type 26 vector platform*[2] and is administered as a single intramuscular dose, whereas the first two authorized vaccines use an mRNA platform and require 2 doses. On February 28, 2021, the Advisory Committee on Immunization Practices (ACIP) issued interim recommendations for use of Janssen COVID-19 vaccine among persons aged ≥18 years.[3] During April 13–23, CDC and FDA recommended a pause in use of Janssen vaccine after reports of six cases of cerebral venous sinus thrombosis (CVST) with thrombocytopenia (platelet count <150,000/μL of blood) among Janssen vaccine recipients.[4] Similar thrombotic events, primarily among women aged <60 years, have been described in Europe after receipt of the AstraZeneca COVID-19 vaccine, which uses a replication-incompetent chimpanzee adenoviral vector.[5–7] The U.S. CVST cases that prompted the pause in Janssen vaccination, as well as subsequently detected CVST cases, are described elsewhere.[8] This report summarizes adverse events among Janssen vaccine recipients, including non-CVST cases of thrombosis with thrombocytopenia syndrome (TTS), reported to the Vaccine Adverse Events Reporting System (VAERS), a passive surveillance system, and through v-safe, an active monitoring system. As of April 21, 2021, 7.98 million doses of the Janssen COVID-19 vaccine had been administered. Among 13,725 VAERS reports reviewed, 97% were classified as nonserious and 3% as serious, including three reports among women of cases of thrombosis in large arteries or veins accompanied by thrombocytopenia during the second week after vaccination. These three cases and the previously detected CVST cases are consistent with 17 cases of TTS,§ a newly defined condition. Approximately 338,700 Janssen COVID-19 vaccine recipients completed at least one v-safe survey during the week after vaccination; 76% reported a systemic reaction, 61% reported a local reaction, and 34% reported a health impact. Fatigue and pain were commonly reported symptoms in both VAERS and v-safe. The overall safety profile is consistent with preauthorization clinical trials data. Prompt review of U.S. vaccine safety data detected three additional cases of non-CVST TTS, in addition to the previously recognized CVST cases that initiated the pause in use of the Janssen COVID-19 vaccine. Ongoing monitoring of adverse events after COVID-19 vaccination, including vaccination with the Janssen single-dose vaccine, is essential for evaluating the risks and benefits of each vaccine.

VAERS is a national passive surveillance program managed by CDC and FDA that monitors adverse events after all vaccinations.[9] VAERS reports are accepted from health care providers, vaccine manufacturers, and the public. Under EUAs for each COVID-19 vaccine, health care providers are required to report several types of adverse events to VAERS, including all deaths.** Signs and symptoms in VAERS reports are coded using the Medical Dictionary for Regulatory Activities (MedDRA).†† VAERS staff members attempt to obtain medical records and supporting information from health care providers for all reported serious events, as well as death certificates and autopsy reports for all deaths.

V-safe is a new, voluntary text-based surveillance system designed to collect additional information about COVID-19 vaccine adverse events, particularly for common side effects.§§ Vaccine recipients who enroll in v-safe receive regularly scheduled text message reminders to complete short online health surveys that include questions about local injection site and systemic reactions and health impacts (i.e., whether the enrollee was unable to perform normal daily activities, missed work, or received care from a medical professional because of new symptoms or conditions).¶¶ Enrollees who report seeking medical care are contacted by CDC's v-safe call center and encouraged to complete a VAERS report, if indicated.

In this report, VAERS and v-safe data are described by sex, age group, and race/ethnicity of vaccine recipients. VAERS data include reports received and processed during March 2–April 21. V-safe data from persons vaccinated during March 2–April 12 were analyzed to permit time for respondents to complete up to eight daily health surveys after vaccination. These activities were reviewed by CDC and are consistent with applicable federal law and CDC policy.***

As of April 21, 2021, 7.98 million doses of Janssen COVID-19 vaccine had been administered in the United States, 50% to women. The median age at vaccination was 50 years. Race/ethnicity was unknown for 39% of persons vaccinated; 38% were non-Hispanic White (White).

*The Janssen COVID-19 vaccine contains double-stranded DNA encoding a variant of the SARS-CoV-2 spike glycoprotein inserted into a replication-incompetent human adenovirus type 26 virus.
VAERS reports are classified as serious if any of the following are reported: death, life-threatening illness, hospitalization or prolongation of hospitalization, permanent disability, congenital anomaly, or birth defect.
§Brighton Collaboration's draft interim case finding definition for TTS: any patient presenting with acute venous or arterial thrombosis and new onset thrombocytopenia, with no known exposure to heparin or any other underlying condition or explanation for the condition.
A health impact was defined as being unable to perform normal daily activities, being unable to work, or receiving medical care.
††Each VAERS report might be assigned more than one MedDRA preferred term. A MedDRA coded event does not indicate a medically confirmed diagnosis.
¶¶CDC has encouraged jurisdictions receiving COVID-19 vaccines to offer v-safe promotional materials, supplied by CDC, at all vaccination sites. V-safe enrollees receive daily health check-ins via text messages that link to web-based surveys on days 0–7 after vaccination; then weekly through 6 weeks after vaccination; and then 3, 6, and 12 months after vaccination.
***45 C.F.R. part 46, 21 C.F.R. part 56; 42 U.S.C. Sect. 241(d); 5 U.S.C. Sect. 552a; 44 U.S.C. Sect. 3501 et seq