The U.S. Food and Drug Administration issued its final guidelines for approving a COVID-19 vaccine. Under the advisory, a vaccine candidate must be at least 50% effective in treating COVID-19 to be approved by the agency.

The news of the guidelines comes as Russia announced that it had approved its own vaccine. The announcement was greeted with skepticism because of a lack of widespread clinical testing to prove its safety and efficacy.

The FDA guidelines allow for emergency use authorization for a vaccine but note it would be difficult to determine the vaccine’s effectiveness before a large-scale clinical trial is conducted.

To date, there are six vaccines currently in phase 3 clinical trials as determined by the World Health Organization. The Russian vaccine was not one of those listed.

Many of the companies developing a COVID-19 vaccine said they are looking to deliver it by the end of the year or in early 2021.

The FDA said it could issue an emergency use authorization if there is enough data on the safety and efficacy of a vaccine, but it would prefer more scientific testing prior to making the decision.

Without emergency use authorization, vaccine producers would need to conduct animal studies to prove that a worsened infection would not occur from the vaccine, and a 50% effectiveness in a placebo-controlled trial would need to be obtained, the FDA said.