The Russian developer of the Sputnik V coronavirus vaccine said on Thursday it would sue the Brazilian health regulator Anvisa for defamation, prompting a stern rebuttal from the agency.

Anvisa's board on Monday denied requests by Brazilian states to approve Sputnik V for import. The agency's manager for medicines and biological products, Gustavo Mendes, said there was evidence an adenovirus used in the vaccine could reproduce, which he called a "serious" defect...