A booster dose of Johnson & Johnson Inc's single-dose COVID-19 vaccine was 84 per cent effective at preventing hospitalisation 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The real-world study, which has not been peer-reviewed, was based on a second dose of the J&J vaccine administered to 69,092 healthcare workers between November 15 and December 20.
An initial course of inoculation has been shown to offer greatly reduced protection against Omicron, particularly against infection. However, several studies have suggested that a booster dose still provides significant protection against severe illness.
The new South African study of the J&J shot showed that the vaccine's effectiveness at preventing hospitalisation rose from 63 per cent shortly after a booster was administered to 84 per cent 14 days later. Effectiveness reached 85 per cent at one to two months post-boost.
Earlier this month, another South African-based study showed that a first round of inoculation with two doses of Pfizer-BioNTech's COVID-19 vaccine had been less effective in South Africa at keeping people infected with the virus out of hospital since the Omicron variant emerged last month.
The trial has been evaluating the efficacy of the J&J vaccine in the field after it was temporarily suspended due to concerns over extremely rare cases of blood clots.
Scientists in South Africa first alerted the World Health Organisation that they had detected Omicron in late November. The highly-mutated variant has spread quickly in other countries, and is fueling a new wave of infections.