Researchers said those aged 60 and over were slower to respond to the BBIBP-CorV vaccine, but they said it was “encouraging” that the vaccine did trigger such a response, ITV reported.
They also found antibody levels to be lower in those aged 60 to 80 years, compared with those aged 18 to 59.
The researchers said the trial was not designed to assess efficacy of the vaccine so it they could not conclude whether the antibody responses induced by the vaccine could protect from coronavirus infection.
The research, published in the journal Lancet Infectious Disease, is based on small early phase randomised clinical trials involving 640 participants.
“Protecting older people is a key aim of a successful Covid-19 vaccine”, Professor Xiaoming Yang said.
Study author Professor Xiaoming Yang, from the Beijing Institute of Biological Products Company Limited, said: “Protecting older people is a key aim of a successful Covid-19 vaccine as this age group is at greater risk of severe illness from the disease.
“However, vaccines are sometimes less effective in this group because the immune system weakens with age.
“It is therefore encouraging to see that BBIBP-CorV induces antibody responses in people aged 60 and older, and we believe this justifies further investigation.”
Inactivated vaccines are those that contain whole viruses that have been killed or small parts of viruses, such as proteins or sugars, that cannot cause disease.
The first phase of the study was designed to find the optimal safe dose for BBIBP-CorV, in which 192 participants aged between 18 and 80 received either the vaccine or a placebo.
In the second phase of the study, 448 participants aged between 18 and 59 were randomly assigned to receive either one eight-microgram shot of vaccine or placebo, or two shots of four micrograms or placebo at zero and 14 days, zero and 21 days or zero and 28 days.
The researchers said no serious adverse events were reported within 28 days of the final vaccination, while the most common side-effect was pain at the injection site, although a small number of participants reported experiencing a fever.
Prof Yang added: “Our findings indicate that a booster shot is necessary to achieve the greatest antibody responses against Sars-CoV-2 and could be important for protection.”
The authors said there were some limitations to their study, one of which includes a short follow-up duration of just 42 days.