Johnson & Johnson on Friday said its single-shot coronavirus vaccine was 72% effective in preventing moderate-to-severe COVID-19 in the U.S, but fell to 66% in a larger trial conducted worldwide. The results stem from a Phase 3 ENSEMBLE clinical trial, which involved 43,783 participants.

The shot was found to be 66% effective in preventing moderate-to-severe illness in Latin America, and 57% effective in South Africa at 28 days post-vaccination. When the company only looked at severe cases, protection rose to 85%.

J&J’s vaccine differs from currently approved jabs in the U.S. in that it requires a single shot as opposed to two doses, and was created using an adenovirus rather than mRNA technology.

"Johnson & Johnson embarked on the global effort to combat the COVID-19 pandemic a year ago, and has brought the full force of our capabilities, as well as tremendous public-private partnerships, to enable the development of a single-shot vaccine. Our goal all along has been to create a simple, effective solution for the largest number of people possible, and to have maximum impact to help end the pandemic," Alex Gorsky, Chairman, Board of Directors and Chief Executive Officer, Johnson & Johnson said in a press release Friday. "We’re proud to have reached this critical milestone and our commitment to address this global health crisis continues with urgency for everyone, everywhere."

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The company suggested the shot was safe and well-tolerated; 9% of trial participants developed a fever and there were no serious allergic reactions. 

J&J also boosted hopes its vaccine candidate will be effective against variant strains.

"Protection was generally consistent across race, age groups, including adults over 60 years of age (N= 13,610), and across all variants and regions studied, including South Africa where nearly all cases of COVID-19 (95%) were due to infection with a SARS-CoV-2 variant from the B.1.351 lineage," reads the release.

The company said it plans to file for an emergency use authorization (EUA) in the U.S. in early February, with product ready to ship immediately after authorization. The company expects the vaccine to remain stable for two years at minus 20 degrees Celsius, and at least three months at 2 degrees Celsius to 8 degrees Celsius.

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Top officials with the U.S. Centers for Disease Control and Prevention (CDC) weighed in on the results Friday. One voiced disappointment in the vaccine's efficacy compared to previously authorized shots developed by Pfizer-BioNTech and Moderna, which are about 95% effective against COVID-19.

"Any vaccine is better than no vaccine as long as it meets the standards required under the EUA," Dr. John Brooks, the CDC’s chief medical officer of COVID-19 response, who was participating in the Infectious Diseases Society of America briefing, said on Friday. "In the event you have the chance to be vaccinated, I encourage you to take the vaccine you are given as long as it meets the requirements under the FDA EUA."

Dr. Jay Butler, the CDC’s deputy director of infectious diseases, said that while the 66% efficacy is "disappointing compared" to the mRNA vaccines, the agency would "be celebrating the seasonal influenza vaccine with a 60% efficacy."