Brazil’s Covid-19 vaccination program is being put at risk by people failing to show up for their second shot, with 1.5 million people missing appointments for the follow-up dose needed to maximize protection, according to the Health Ministry. Specialists say that is particularly concerning after a recent real-world study from Chile found that the Sinovac Biotech (SVA.O) Covid-19 vaccine, which has accounted for some 80% of Brazil's program, is just 16% effective after one shot. “Without the two doses, we get neither full protection nor a long duration of protection,” Juarez Cunha, head of the Brazilian Society of Immunizations, told Reuters. “We need people to do the full cycle.”