FDA and CDC release statement recommending pauseSix reported US cases of ‘rare and severe problem’ Johnson & Johnson developed a single-shot Covid-19 vaccine. Photograph: Tom Williams/CQ-Roll Call, Inc/Getty Images US health agencies have recommended states pause the administration of the Johnson & Johnson coronavirus vaccine, after reports of rare and severe blood clots emerged in six women. More than 6.8m doses have been administered nationally. The concerns mirror those of drugs agencies in Europe and Australia over the AstraZeneca vaccine, which has not authorized in the US. There have been no significant safety concerns raised about the two other vaccines that make up the majority of US supply, from Pfizer-BioNTech and Moderna. The FDA and CDC said in a joint statement: “People who have received the J&J vaccine who develop severe headache, abdominal pain, leg pain, or shortness of breath within three weeks after vaccination should contact their healthcare provider.” All six women were between the ages of 18 and 48. One woman died, and a woman in Nebraska is hospitalized in critical care, according to the New York Times. Johnson & Johnson’s vaccine is also under scrutiny by the European Medicines Agency, which is investigating four cases of clotting. Health agencies said the blood clotting concern is “extremely rare”. Authorities are still investigating whether the clotting is indeed caused by the vaccine. Technically, the disorder is a thrombosis, or blood clot, with thrombocytopenia, a low count of platelets, the component of blood responsible for clotting. The same symptoms have been observed in a very small number of AstraZeneca recipients. As of 4 April, there have been 222 cases of blood clots among the more than 34 million globally who have received the AstraZeneca vaccine. The European Medicines Agency has examined 86 cases of blood clots, 18 of which have been fatal. J&J said in a statement: “The safety and wellbeing of the people who use our products is our No 1 priority. At present, no clear causal relationship has been established between these rare events and the Janssen Covid-19 vaccine. We continue to work closely with experts and regulators to assess the data and support the open communication of this information to healthcare professionals and the public.” Janssen is the division of Johnson & Johnson that developed the vaccine. J&J and AstraZeneca use a vaccine technology called an adenovirus platform to prompt immunity. The technology uses a second, weakened cold virus to deliver the genetic payload of the coronavirus to the immune system, and spur the body to make antibodies. However, a mechanism that may cause the potential connection between clotting and the adenovirus platform is not clear. Moderna and Pfizer use a different vaccine platform called messenger RNA, to provoke the body to build antibodies. Independent experts have said the “pause” in administration shows federal monitoring systems for potential adverse side effects of the vaccine are working. Ashish Jha, the dean of the Brown University school of public health, said on Twitter: “My sense is confidence comes from people believing that we have a vigorous system that takes adverse events seriously.” He said, “while unfortunate,” the pause is the “right step”. Scott Gottlieb, a former FDA commissioner, said on CNBC’s Squawk Box: “For most consumers, I wouldn’t be concerned about this. Really this is an alert to doctors. That’s how FDA framed it. It’s advice to doctors to be monitoring more closely.” The pause in administration of the Johnson & Johnson vaccine may also cause a hit to the American immunization campaign, which was set to administer hundreds of thousands of easy-to-administer doses provided by the company. The White House denied the pause would have a significant impact. Jeff Zients, the White House Covid response chief, said: “This announcement will not have a significant impact on our vaccination plan. [The] vaccine makes up less than 5% of the recorded shots in arms in the US to date.” Johnson & Johnson’s vaccine requires only one dose, and can be stored in a common refrigerator. Pfizer and Moderna’s vaccine require ultra-cold storage and a two-dose regiment. The pause represents a blow to Johnson & Johnson, which recently was forced to throw away between 13m and 15m doses of vaccine after a federal contractor botched doses. The J&J pause at a perilous time in the pandemic. In spite of the strides made in immunizing all adult Americans, with 74 million people and 22% of the public fully immunized, Covid-19 cases are rising in several states, such as Minnesota, and remain high in others, such as Michigan. With a weary public and the return of warm weather in much of the country, politicians have had little appetite to renew restrictions on social life and many instead say the vaccination campaign can curb cases. The new concerns are also likely to inflame partisan tensions and the conspiracy theorists. Republicans, especially men, remain the most hesitant to receive a coronavirus vaccine after national politicians and Donald Trump downplayed the seriousness of the virus. Vaccine hesitancy could play an increasingly significant role in whether the US is able to curb the pandemic, or if the viral spread is allowed to continue and circulate regionally. Although the exact level of immunity needed to squash viral spread is not known, experts believe between 70-90% of the public will need to be vaccinated. Because children make up about a quarter of the US population, that level of immunity would require nearly every US adult to be vaccinated to stop spread. Federal regulators said they will convene an emergency meeting of vaccine regulators to discuss the matter. A press conference was expected on Tuesday morning.