Doses of the Janssen COVID-19 vaccine are now available to those in the Military Health System eligible and authorized to receive COVID-19 vaccinations, said Air Force Col. Jennifer Garrison, DOD COVID-19 Vaccine Program Operation Team Lead for the Department of Defense.

The Food and Drug Administration and the Centers for Disease Control and Prevention gave the greenlight to resuming use of the Janssen (also called Johnson & Johnson) vaccine April 23.

Aligning to the CDC, the MHS plan was subsequently approved by the White House and the CDC, Garrison said.

Defense Health Agency Director Army Lt. Gen. (Dr.) Ronald Place said: "We have full confidence that the J&J vaccine is safe and effective in preventing COVID-19 and that the data shows the vaccine's known potential benefits outweigh its known and potential risks."

The vaccine received FDA emergency use authorization Feb. 27 and was put on pause by the FDA and the CDC April 13 due to a small instance of those vaccinated with the Janssen product developing a rare, but serious blood clotting disorder that has now been named Thrombosis with Thrombocytopenia Syndrome (TTS).

TTS occurred at a rate of about 7 per 1 million vaccinated women between the ages of 18 and 49. For women 50 and older and men of all ages, this adverse event is even more rare.

FDA has added a warning to the Janssen COVID-19 vaccine emergency use authorization and fact sheets regarding the clotting events, CDC said. As of April 23, TTS had not been linked to the Pfizer-BioNTech or Moderna vaccines.

As of April 21, approximately 7.98 million doses of the Janssen COVID-19 vaccine had been administered in the United States, the CDC said in a report released April 27.

More than 2.62 million doses of the Pfizer-BioNTech, Moderna, and Janssen COVID-19 vaccines have been given to those eligible and authorized within the Military Health System (MHS), and more than 438,000 have been administered to MHS beneficiaries at retail pharmacies and other non-DOD sites, Place explained during a news conference April 21.

The Janssen vaccine makes up less than 3% of the doses provided to the Department of Defense, according to the DOD.

So far, Place said, there have been no cases reported in the military of the blood clotting serious adverse event, but data are being reviewed.

Out of an abundance of caution, CDC said it would review the Janssen data through its Advisory Committee on Immunization Practices (ACIP). The committee met April 14 and decided to keep the pause in vaccinations in place while it further reviewed the data from the Janssen large-scale clinical trials and the adverse events. On April 23, the ACIP recommended the restart of Janssen vaccinations.

A review of all available data shows that the one-shot Janssen COVID-19 vaccine's "known and potential benefits outweigh its known and potential risks for those recommended to receive it," the CDC announced April 25.

However, "women younger than 50 years old should be aware of the rare but increased risk of the TTS adverse event, and that there are other COVID-19 vaccine options available for which this risk has not been seen," CDC said.

People who have received the Janssen vaccine who develop severe headaches, abdominal pain, leg pain, or shortness of breath within three weeks after vaccination should contact their health care provider, the CDC said.

The pause allowed the CDC to re-emphasize with health care providers the importance of reporting severe events in people who have received this vaccine, as well as how to report such events. The pause also gave experts time to carefully review all available data and conduct a risk-benefit analysis of the vaccine.

Military vaccination sites have continued local planning and messaging for reintroduction of the Janssen vaccine. Any products or processes that need to be changed based on the CDC's April 27 "Morbidity and Mortality Weekly Report" and its clinicians' briefing will be finalized April 28, Garrison said. The DHA Director's directive to resume vaccinations with any additional guidance or changes required will be produced and published.

The Janssen vaccine is a replication-deficient adenovirus-vectored vaccine like the AstraZeneca/Oxford vaccine, which has not yet received FDA emergency use authorization.

This means it uses a different virus, such as measles or adenovirus, which is genetically engineered so that it can produce coronavirus proteins in the body and trigger the immune system to make antibodies against those proteins.

The viruses used in viral-vector vaccines are weakened or inactivated, so they cannot cause disease or harm humans. Viral-vector vaccines are also relatively fragile and must be maintained at temperatures that allow them to remain intact to work optimally.

The resource center on the Pfizer, Moderna and Janssen vaccines provides a plethora of information for MHS health care professionals.