What Are TTS Blood Clots? J&J Vaccine Risks, Benefits to Be Discussed by CDC Advisers

U.S. health officials are due to meet on Thursday to discuss the benefits and risks of the Janssen COVID vaccine made by Johnson & Johnson.

A draft agenda for a meeting of the Advisory Committee on Immunization Practices (ACIP) was released by the Centers for Disease Control and Prevention (CDC) on Wednesday. It said experts would have a vote on "updated recommendations for use" of the J&J vaccine.

The meeting is also due to involve updates on a newly described condition known as Thrombosis with Thrombocytopenia Syndrome (TTS), which has been identified as a rare potential side-effect of certain COVID vaccines.

According to the American Society of Hematology (ASH), vaccine-induced TTS is defined as any thrombosis—a blood clot—in a vein or artery, with thrombocytopenia, or a low blood platelet count, within four to 42 days after having a COVID vaccine.

The ASH said as of August 12 that incidence of the condition was "extremely low," but that an urgent medical evaluation was needed for people with symptoms such as severe headaches, visual changes, abdominal pain, nausea, back pain, shortness of breath, leg pain and swelling, as well as easy bruising or bleeding within four to 42 days after vaccination.

It also noted TTS appeared "far more likely" to occur after the J&J or AstraZeneca vaccines, which are a type known as adenoviral vector vaccines, than with the Moderna or Pfizer vaccines, which are a type known as mRNA vaccines.

According to the CDC, as of November 24 more than 16.4 million doses of the J&J vaccine had been given to people in the U.S. and 54 of those people later developed TTS. That compared to two confirmed TTS cases following a vaccination with the Moderna shot after 437 million mRNA vaccine doses had been administered in the country.

On October 8 this year, the Australian government published data on TTS occurrence following a first dose of the AstraZeneca vaccine and found that the risk was around 2.4 per 100,000 in people aged under 60 and 1.8 per 100,000 in people aged 60 or older.

Importance of Booster Shots

As of Thursday morning the CDC continued to recommend the use of the J&J COVID vaccine in people aged 18 and older, though it noted that women younger than 50 should be especially aware of "the rare but increased risk of TTS," which it described as "a serious condition that involves blood clots with low platelets."

The meeting comes as scientists around the world are stressing the importance of booster vaccines amid the rise of the Omicron variant of COVID, which may be highly resistant to existing vaccines, according to early data.

On December 9, the CDC strengthened is booster recommendations and encouraged everyone 16 and older to go and get one, with CDC Director Dr Rochelle Walensky saying that "initial data suggests that COVID-19 boosters help broaden and strengthen the protection against Omicron and other variants."

As of December 15, more than 186 million, or 72.2 percent, of U.S. citizens over the age of 18 had been fully vaccinated against the coronavirus, according to CDC data. About 56 million, or 30 percent, had received a booster shot.

Janssen COVID vaccine
A close-up photo of a Janssen vaccine vial taken in Nieuwegein, the Netherlands, on June 25, 2021. U.S. health officials are due to discuss the Janssen vaccine on Thursday. Patrick van Katwijk/BSR Agency / Getty