By Wendell Roelf

CAPE TOWN (Reuters) -A booster dose of Johnson & Johnson (NYSE:) Inc’s single-dose COVID-19 vaccine was 84% effective at preventing hospitalization in South African healthcare workers who became infected as the Omicron variant spread, researchers said on Thursday.

The real-world study, which has not been peer-reviewed, was based on a second dose of the J&J vaccine administered to 69,092 workers between Nov. 15 and Dec. 20.

Omicron is rapidly spreading in many countries, and it has only been proven that an initial inoculation can offer very limited protection.

Numerous studies suggest that the booster dose may provide significant protection from severe illnesses caused by this variant.

The South African study showed the J&J vaccine’s effectiveness at preventing hospitalization rose from 63% shortly after a booster was administered to 84% 14 days later. After a booster was administered, the vaccine’s effectiveness reached 85%.

Linda-Gail Bekker was the co-lead researcher in the study. “It gives us confidence that COVID-19 vaccinations are still effective for their intended purpose, which is the protection of people against serious disease and death.”

“This is yet more evidence that our impact has not been lost, even when faced with a highly mutated variant.”

Bekker said the jury was “still out” on the issue of further boosters of the J&J shot.

“What we’re showing is that just two doses can restore complete protection. And I don’t believe that it is possible to extrapolate that we would need a third, or fourth boost.”

The researchers noted that their study had limitations. They found that healthcare workers receiving a boost in the past 13 days averaged 8 days. 32 days were for people who received it 1-2 months prior. This could have a negative impact on vaccine effectiveness.

This month, another South African-based study showed that in South Africa, a second round of vaccination with COVID-19 vaccine by Pfizer BioNTech was less effective than a third.