Sinopharm's COVID-19 vaccine was less effective in offering protection against the disease among the elderly, according to the results of a Hungarian study, reports Reuters.
The study of 450 participants who had received two doses of the vaccine showed measurable antibody levels were present in about 90 per cent of people under the age of 50, but the protection reduced as age increased.
The estimated probability of no antibody response was about 25 per cent in people aged 60 and about 50 per cent at the age of 80 years, according to the study, which was published on medRxiv earlier this week and has not been peer-reviewed.
Several elderly subjects were unable to produce any protective antibodies, suggesting that measures should be put in place to prevent an outbreak of COVID-19 among them, the study's authors said.
But the authors warned that the reliable estimation of a direct relationship between the risk of the COVID-19 disease, hospitalisation, or death and the antibody levels after vaccination is extremely difficult.
Sinopharm, formally known as China National Pharmaceutical Group, was not immediately available for comment.
The two-dose vaccine is one of the most widely used COVID-19 shots in China, and Sinopharm has agreed to provide up to 170 million doses of the shot to the global vaccine sharing scheme COVAX through to the middle of 2022.
A recent study showed the vaccine-elicited weaker antibody responses against the Delta variant, which was first found in India and is now the dominant variant worldwide.
