The FDA yesterday set limits on Johnson & Johnson’s Covid-19 vaccine because of the risk of a clotting disorder discovered weeks after the vaccine was first put into use in spring 2021. The agency said its review of the available data on the risk of thrombosis with thrombocytopenia — or TTS — suggested limiting access to the vaccine is warranted. The condition, though rare, can be fatal. The single-dose vaccine will now be available only to adults 18 and older who would not otherwise agree to be vaccinated or who cannot take one of the other available vaccines for medical reasons.