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Rare Risk of Serious Adverse Events After COVID Vaccination

Aug 10, 2021 4:14 pm

The CDC had reported the Advisory Committee on Immunization Practices (ACIP) study of rare serious adverse events after COVID-19 vaccination and assert that the excessive morbidity and mortality from COVID-19 (and the protection afforded by vaccination) far exceeds the risk of rare safety signals reported following vaccination.

Specifically they have examined the risk of Guillain-Barré syndrome (GBS) and thrombosis with thrombocytopenia syndrome (TTS) reported after Janssen COVID-19 vaccination and also the risk o fmyocarditis after mRNA (Pfizer-BioNTech and Moderna) COVID-19 vaccination.

As of July 22, 2021, 187 million persons in the United States had received at least 1 dose of COVID-19 vaccine, and with intensive monitoring methods, serious adverse events following vaccination have been rare.  Most concerning were temporally associated reports of:

  • Thrombosis with thrombocytopenia syndrome [TTS] (venous or arterial thrombosis with thrombocytopenia) 
  • Guillain-Barré syndrome [GBS] (rare autoimmune neurologic disorder of ascending weakness and paralysis)
  • Myocarditis (cardiac inflammation)

In July 2021, ACIP recommended that, overall, the benefits of COVID-19 vaccination in preventing COVID-19 morbidity and mortality outweigh the risks for these rare serious adverse events in adults aged ≥18 years; this balance of benefits and risks varied by age and sex.

Interestingly, TTS and GBS have only been reported after Janssen COVID-19 vaccination; and myocarditis has only been after mRNA COVID-19 vaccinations (especially after the second dose).  Hence, there has been no increased risk detected for GBS or TTS after mRNA COVID-19 vaccination, and there has been no increased risk detected for myocarditis after Janssen COVID-19 vaccination.

GBS: With approximately 12.6 million doses of Janssen COVID-19 vaccine administered to adults in the United States, there have ben 100 reports of GBS after Janssen COVID-19 vaccination. The median age was 57 years (range = 24–76); and the median interval from vaccination to symptom onset was 13 days (range = 0–75 days). Ninety-five (95%) patients experiencing GBS were hospitalized, and 10 (10%) were admitted to an ICU and there has been one death. The most affected group was males aged 50–64 years, with 15.6 cases per million Janssen COVID-19 vaccine doses administered.

TTS: Among 12.6 million doses of Janssen COVID-19 vaccine administered to adults in the United States, 38 cases of TTS within 15 days of vaccination. Four of these patients died. The overall TTS reporting rate was 3.0 cases per million doses administered, with the highest rate among females aged 30–49 years (8.8 TTS cases per million Janssen COVID-19 vaccine doses administered).

Myocarditis:  Approximately 141 million second mRNA COVID-19 vaccine doses had been administered to adults in the United States and there have been 497 reports of myocarditis after the second mRNA COVID-19 vaccine. The reporting rate of myocarditis overall among adults was 3.5 cases per million second doses given with the highest rate among males aged 18–29 years (24.3 cases per million mRNA COVID-19 vaccine second doses administered). There have been no confirmed myocarditis-associated deaths.


The author has no conflicts of interest to disclose related to this subject

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