2 doses of Johnson & Johnson's COVID-19 vaccine 85% effective against hospitalizations, South Africa study shows

A real-world study of South African health care workers found that two doses of the Johnson & Johnson COVID-19 vaccine offer 85% protection against hospitalization from the omicron variant.

Separately, the company announced new data from a laboratory study that shows its vaccine likely also works well as a booster for people who got the Pfizer shots originally.

The lab study specifically tested two types of immune system responses -- antibody and T-cell responses -- against the omicron variant.

Using the J&J vaccine as a booster raised people's antibodies and T-cells to levels higher than those seen among people who got a third dose of Pfizer -- according to samples taken four weeks after each booster.

The new data adds weight to the argument that mixing and matching vaccine types could be an effective strategy, but the data is limited because it was a laboratory study, not real-world data.

The new findings were described in a press release and submitted to pre-print journals.

"As the Omicron variant has mutated from the original SARS-CoV-2 strain, there is a need to understand how effective currently authorized COVID-19 vaccines remain at protecting against severe disease," Dr. Dan Barouch, Ph.D., director of the Center for Virology and Vaccine Research at BIDMC, said in a statement. "Our analysis shows that a booster shot of the Johnson & Johnson COVID-19 vaccine generated a robust increase in both neutralizing antibodies and T-cells to Omicron."

Since its launch, the single-shot J&J vaccine has been dogged by the perception that it is less effective than Pfizer and Moderna's vaccines. And indeed, many experts agree that one dose of J&J isn't as effective as two shots from the other brands; but when given as two doses, the J&J shot seems to be an effective vaccine.

"While one dose to prevent COVID was always desirable to improve vaccine access and acceptance, we now have irrefutable evidence that two doses provides significantly more protection," said John Brownstein, Ph.D, chief innovation officer at Boston Children's Hospital and ABC News contributor. "The second dose triggers the immune system to produce antibodies and memory cells that ultimately yield longer term vaccine effectiveness."

Earlier this month, the Centers for Disease Control and Prevention recommended that anyone considering getting vaccinated should get the Pfizer and Moderna vaccines, if available, over the J&J single-shot vaccine. This isn't because the single-shot J&J vaccine -- which has been associated with a risk of very rare blood clots -- isn't safe and effective, CDC researchers said, but because the Pfizer and Modern two-shot vaccines appear to work even better. Collectively, this means the risk-benefit analysis is more favorable for the Pfizer and Moderna vaccines, the CDC said.