What vaccines are currently available?

Currently, there are three vaccines now authorized and recommended in the United States to prevent COVID-19:

  • Pfizer-BioNTech vaccine (mRNA vaccine)
  • Moderna vaccine (mRNA vaccine)
  • Johnson & Johnson/Janssen (vector-based vaccine)

mRNA Vaccines (Pfizer-BionTech and Moderna)

These vaccines have genetic material called mRNA or “messenger RNA” that is taken from the virus. Once injected, this material tricks our bodies into producing a spike protein unique to the virus. When our immune systems detect this protein, they then create cells that recognize and destroy it. These immune system cells remain in our bodies for long periods, giving us protection against the virus. The mRNA vaccines do not alter your genes, nor can they give you COVID-19.

Vector-based Vaccine (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. It was approved for Emergency Use Authorization on February 27, 2021.  The CDC Advisory Committee on Immunization Practices recommended the vaccine on February 28, 2021.

As of 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