The US laboratory Johnson & Johnson announced on Thursday that the US Food and Drug Administration (FDA) authorized an extension of the shelf life of its COVID-19 vaccine from three months to four and a half months.
"The decision is based on data from the stability assessment studies that are being carried out," the company said in a statement reported by the AFP news agency.
According to the Centers for Disease Control and Prevention, 21 million doses of the vaccine were distributed throughout the United States, but only 11 million have been administered.
Ohio Gov. Mike DeWine warned this week that 200.000 doses in his state will expire on June 23.
Although not as effective in preventing symptomatic covid as the messenger RNA vaccines developed by Pfizer and Moderna, J & J's immunizer, based on adenovirus vector technology, was found to be 85% effective in preventing severe forms of the disease in an important study.
That figure rose to 100% 28 days after the injection. The fact that the vaccine only required one dose was a key selling point in targeting hard-to-reach populations.
Authorities believe that the J&J vaccine carries an increased risk of developing a rare but serious type of clotting that occurs mostly in women between the ages of 18 and 49.
The condition, characterized by a low level of platelets, is called vaccine-induced immune thrombotic thrombocytopenia (TVI).
The United States now has a significant stock of leftover doses, highlighting the growing vaccine disparity between rich and poorer nations.