ST. LOUIS (AP) — Two African lions and six other big cats at the St. Louis Zoo have tested positive for COVID-19.

The St. Louis Post-Dispatch reports that zoo officials said Thursday that the animals are expected to make a full recovery. Besides the lions, two snow leopards two jaguars, an Amur tiger and a puma have been infected.

Most of the infected cats showed no signs of illness, zoo officials said, but a few had a decreased appetite and were less active for short periods of time. Some also developed respiratory symptoms, zoo officials said.

Officials suspect the animals became infected in the window after they had received their first dose of an animal-specific version of the COVID-19 vaccine but before they received their second dose.

“As in humans, we would expect that full protection against this virus would not be developed until a few weeks after the second injection in a series,” said Dr. Sathya Chinnadurai, the zoo’s director of animal health.

An investigation did not reveal the source of the infection, which has been has been limited to Big Cat Country. All staff members are required to be vaccinated and to wear masks indoors and around potentially at-risk animals.

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