Apr. 13, 2021 Citing an “abundance of caution,” federal health officials called for a pause in the use of the Johnson & Johnson vaccine Tuesday, following concerns that the vaccine may be linked to a rare but severe type of blood clotting. The concerns stem from six reported cases of the blood clot in the United States. All of the cases were reported in women under the age of 50. Nearly 7 million doses of the Johnson & Johnson vaccine have been administered in the U.S. That means the blood clotting was reported in about 1 in 1.1 million vaccinations. Some women quickly noted that those rates are far lower than that of some hormonal contraceptives, which also carry risks of blood clotting.