Two doses of China’s Sinovac vaccine offered older people only a moderately high level of protection against severe disease and death from Covid-19, but a third dose significantly bolstered their defenses, according to a new study by scientists in Hong Kong.
The study, based on patients infected during the current devastating Omicron wave in Hong Kong, serves as a cautionary note for mainland China, where Sinovac is a pillar of the country’s vaccination program. Many older people there have yet to receive booster shots.
For people 60 and older, two Sinovac doses were 72 percent effective against severe or fatal Covid-19 and 77 percent effective against Covid-related death, the study found. Those levels of protection were lower than those provided by two Pfizer-BioNTech doses. The same study found they were 90 percent effective against severe or fatal Covid and 92 percent effective against death among Hong Kong residents of the same age group.
A Sinovac booster shot helped considerably, proving to be 98 percent effective against severe or fatal Covid among people at least 60 years old, the study found.