Are the vaccines safe? (Updated*)

Are the vaccines safe?

To be administered in the United States, a COVID-19 vaccines needs an emergency use authorization by the FDA, and their approval process also includes public and independent review from members of the agency’s Vaccines and Related Biological Products Advisory Committee.  Adverse events are being tracked and all participants are asked to report side effects through the CDC V-safe smartphone tool.  Vaccine providers are required to report vaccine-related adverse events to the Vaccine Adverse Event Reporting System (VAERS).

Pfizer-BioNTech and Moderna

Because it is not a live vaccine, you cannot get COVID-19 from the mRNA vaccines. Also, they do not enter the nucleus of the cell and therefore cannot alter your genes. During the trials, there were no reported serious side effects from these two vaccines. Since becoming available to the first priority groups, there have been rare reports of allergic reactions/other serious adverse events with millions of doses given.

Johnson & Johnson

The Johnson and Johnson (Janssen) vaccine is a one dose, adenovirus-based vaccine. Researchers genetically altered a weakened version of a common cold virus (adenovirus) that causes infections in so it carried a gene for the COVID-19 spike protein; this will train a person’s immune system to recognize the real coronavirus. You cannot get COVID-19 from this vaccine. During clinical trial, this vaccine was well tolerated. Serious adverse events, excluding those related to confirmed COVID-19, were reported by 0.4% (n=83) of individuals who received the Johnson & Johnson COVID-19 Vaccine (N= 21,895) and 0.4% (n=96) of individuals who received placebo (N= 21,888).

On April 25, 2021, after a brief pause, CDC and FDA recommended use of Johnson & Johnson’s Janssen COVID-19 vaccine resume in the United States. Previously, administration of this vaccine was paused on April 12 after reports of a rare and severe type of blood clot in 6 U.S. individuals and 1 death.

After a review of all available data, CDC and FDA have concluded that at this time, J&J/Janssen COVID-19 vaccine’s known and potential benefits outweigh its known and potential risks. CDC also states on its website that women younger than 50 years old especially should be aware of the rare but increased risk of this adverse event and that there are other COVID-19 vaccine options available for which this risk has not been seen.

Overall, the research is beginning to emerge on potential relationship of cerebral venous sinus thrombosis (CVST) with thrombocytopenia and adenoviral vector COVID-19 vaccine. A case series of 12 U.S. patients who received J&J/Janssen vaccine and developed CVST and thrombocytopenia as reported to VAERS between March 2 and April 21, 2021 and published on April 30, 2021 looked at the characteristics of these patients. It found following with respect to the patient characteristics who received this type of vaccine and developed subsequent CVST with thrombocytopenia:

  • Seven patients had at least 1 CVST risk factor, including obesity (n = 6), hypothyroidism (n = 1), and oral contraceptive use (n = 1); none had documented prior heparin exposure.
  • Time from vaccination to symptom onset ranged from 6 to 15 days. Eleven patients initially presented with headache; 1 patient initially presented with back pain and later developed headache. Of the 12 patients with CVST, 7 also had intracerebral hemorrhage; 8 had non-CVST thromboses.
  • 11 patients tested for the heparin-platelet factor 4 HIT antibody had positive results.
  • 10 patients were hospitalized in ICU. Outcomes were death (n = 3), continued ICU care (n = 3), continued non-ICU hospitalization (n = 2), and discharged home (n = 4).


Updated: May 5, 2021