As coronavirus cases continue to climb, researchers are beginning to realize that while testing COVID-19 vaccines on animals is required by the Food and Drug Administration (FDA), it isn’t the only option or the most effective one.

More than 150 COVID-19 vaccines are currently in development around the world. In the process, thousands of mice, monkeys, and other species are being used in research experiments.

During COVID-19 vaccine tests, researchers may inject animals with vaccines and then purposely infect them with the virus. In early trials, the Centers for Disease Control and Prevention (CDC) report that monkeys have shown signs of sickness when infected and that ferrets, cats, and hamsters have spread the infection to other animals in laboratories. But after nearly 60 years of research, experts are not certain that drugs and vaccines tested on animals can be effectively translatable to humans.