Johnson & Johnson says its single-shot COVID-19 vaccine is effective in preventing severe cases of COVID-19, but not as well as other two-shot variants of the vaccine that are already on the market.

The company released results from its Phase 3 trial on Friday, saying that it was 66% effective in preventing moderate to severe cases of the virus, and 85% effective in preventing the most severe cases of COVID-19.

By contrast, two-shot vaccines made by Pfizer and Moderna were both more than 90% effective in preventing COVID-19. However, because the Johnson & Johnson shot only requires a single dose, a large supply of the vaccine could potentially solve some logistical problems in widespread distribution.

Johnson & Johnson also said that the vaccine candidate performed better in the U.S. than it did in South Africa, where a mutated form of the virus is spreading throughout the country. According to the Associated Press, the vaccine was 72% effective in preventing moderate to severe cases of COVID-19 in the U.S., while only 57% effective in South Africa.

The company says it will file for Emergency Use Authorization within a week. Johnson & Johnson has already committed to providing 100 million doses of the vaccine by June and could provide doses as soon as it is cleared by the CDC and FDA.