On Saturday, the U.S. Food and Drug Administration (F.D.A.) granted Johnson & Johnson's (JNJ  ) request to allow the company's one-shot coronavirus vaccine to be approved for emergency use. This authorization gives the United States a third effective vaccine against the pandemic, even as highly contagious variants remain at play across the country.

The federal health regulator approved the use of Johnson & Johnson's vaccine for people aged 18 years or older. Just like the emergency use authorizations (E.U.A.) given to the mRNA vaccines developed by Pfizer (PFE  )-BioNTech (BNTX  ) and Moderna (MRNA  ), this is not a full approval from the F.D.A. In order for a vaccine to receive full approval, researchers would have to submit at least six months of safety data, whereas an E.U.A. only requires two months. The company plans to file for a Biologics Licenses Application later this year.

The F.D.A.'s decision was expected, following the unanimous recommendation to approve the one-shot vaccine for public use from the regulator's Vaccines and Related Biological Products Advisory Committee. The group of independent scientists and health experts plays a key role in approving vaccines in the U.S.

Johnson & Johnson found that it's vaccine's level of protection varied by region studied in its late stage clinical trials, the company outlines in the vaccine data it submitted to the F.D.A. The drugmaker found that the shot was overall 66% effective at preventing severe coronavirus infection, while in the U.S. it was 72%, in Latin America is was 66%, and in South Africa--where the concerning B.1.351 variant strain is rapidly spreading--it was 57%. However, the vaccine demonstrated that it was 64% effective in South Africa a month after initial inoculation in later data analysis.

Comparatively, Pfizer's vaccine was found to be 95% effective at preventing norovirus infection, while Moderna's demonstrated roughly 94% efficiency. Both mRNA vaccines require two doses administered about 21 to 28 days apart.

Importantly, Johnson & Johnson found that the vaccine prevented 100% hospitalizations and deaths, meaning that while it may not be fully effective at preventing infection, it will still help combat the virus overall.

"We believe the Johnson & Johnson single-shot COVID-19 vaccine is a critical tool for fighting this global pandemic, particularly as it shows protection across countries with different variants. A vaccine that protects against COVID-19, especially against the most dire outcomes of hospitalization and death, will help ease the burden on people and the strain on health systems worldwide," said CEO Dr. Paul Stoffels in a statement.

The F.D.A. did not identify any safety concerns with the one-shot vaccine, with its most common side effects being headaches, fatigue, muscle pain.

Johnson & Johnson stated that it plans to ship its vaccine, which contains five doses per vial, at average refrigerator temperatures, about 36 to 46 degrees Fahrenheit (2 to 8 degrees Celsius). For comparison, Pfizer's vaccine needs to be shipped and stores at ultra-cold freezer temperatures ranging from -112 to -76 degrees (-80C to -60C) and Moderna's vaccine needs to be shipped at -13 to 5 degrees (-13C to -15C).

The Biden administration has already moved to distribute the one-shot vaccine, with U.S. Centers for Disease Control and Prevention Dr. Rochelle Walensky tweeting on Sunday that the federal health agency has recommended the use of the vaccine in those 18 years of age and older.

"Today marks an encouraging step toward an end to the #COVID19 pandemic," Walensky wrote on Twitter. "I have now signed CDC's Advisory Committee on Immunization Practices' (ACIP) recommendation that endorse the safety and effectiveness of Janssen's COVID-19 vaccine for people 18 & up."