CDC Says Serious Adverse Events Remain ‘Rare’ Following COVID-19 Vaccination

The Centers for Disease Control and Prevention (CDC) is standing behind the safety of 2 prominent coronavirus disease 2019 (COVID-19) vaccines, calling incidences of major adverse events “rare.”

The agency made the declaration in its August 13 Morbidity and Mortality Weekly Report following the July 22 meeting of the agency’s Advisory Committee on Immunization Practices (ACIP).

“The estimated benefits (prevention of COVID-19 disease and associated hospitalizations, ICU admissions, and deaths) outweighed the risks... in all persons aged ≥18 years included in this analysis,” wrote corresponding author Hannah Rosenblum, MD, and colleagues. Rosenblum is a member of the CDC’s COVID-19 Response Team and its Epidemic Intelligence Service.

The Food and Drug Administration (FDA) granted emergency authorization to the 2-dose Pfizer/BioNTech and Moderna vaccines back in December; Johnson & Johnson’s single-dose vaccine gained the same status in February of this year. As of the July ACIP meeting, some 187 million Americans had received at least one vaccine dose.

Though the vaccines have been credited with helping to slow the spread of the SARS-CoV-2 virus and curb hospitalizations and deaths, there have been isolated reports of significant adverse events.

The new report focuses on 3 types of adverse events: myocarditis following the Pfizer/BioNTech vaccine (particularly after the second dose), and thrombosis with thrombocytopenia (TTS) and Guillain Barré syndrome (GBS) following the Johnson & Johnson vaccine.

ACIP used reports submitted through the CDC’s Vaccine Adverse Event Reporting System (VAERS) to re-weigh the costs and benefits associated with the vaccines in light of those reports and the ongoing pandemic. Their calculations looked at the risk of each adverse event per million doses in adults 18 and older, as well as the benefits, assuming a 95% vaccine effectiveness rate for the Pfizer/BioNTech vaccine and a 90% vaccine effectiveness rate for the Johnson & Johnson vaccine.

Between February and June, 100 cases of GBS following the Johnson & Johnson vaccine were reported through VAERS. The median age was 57 years for patients, 61 patients were male, the median time from vaccination to symptom onset was 13 days (though it took 75 days in one patient), and 95% of patients ended up in the hospital. Ten patients were admitted to the ICU. As of the report, one patient had died. ACIP calculated that the unadjusted rate of GBS cases following vaccination was approximately 20.2 per million doses.

As of July 8, 38 cases of TTS had been reported within 15 days of vaccination with the Johnson & Johnson (Janssen) dose. Those cases were each reviewed and confirmed by physicians at the FDA and CDC. As of the report, 4 patients had died. Females ages 30-49 were the most likely to experience TTS following vaccination, and ACIP calculated a TTS report rate of 3.0 per million doses.

For myocarditis, 497 patients reported the condition following their second shot, resulting in a reporting rate of 3.5 cases per mission second doses. Males between the ages of 18 and 29 were most likely to experience myocarditis following vaccination. There have been no reports of deaths associated with post-vaccine myocarditis.

Based on those data, as well as the ongoing risk of COVID-19 transmission, ACIP said the benefits of vaccination outweigh the risks, though they said continued vigilant monitoring is “critical,” as is transparency with the public and patients about the risks.

“ACIP emphasized the importance of informing vaccination providers, and all persons receiving COVID-19 vaccines about the benefits and risks, including the risks after Janssen COVID-19 vaccination for GBS, particularly in males aged 50–64 years, and for TTS among females aged 30–49; and the risk for myocarditis after mRNA COVID-19 vaccination, particularly in males aged 18–29 years,” Rosenblum and colleagues said.

Given the rapid spread of the Delta variant, the CDC said, vaccination “is more urgent than ever.”

The CDC said both it and the FDA have updated their guidance and approval documents in order to ensure patients are fully informed.