One of China's leading COVID-19 vaccine candidates, called BBIBP-CorV, was shown to be safe and elicited immune response in a small early-phase human trial, researchers said on Friday. A previous clinical trial reported similar results for a different vaccine that is also based on inactivated whole SARS-CoV-2 virus, but in that study the vaccine was only tested in people aged under 60 years.
The latest study, published in The Lancet Infectious Diseases journal, included participants aged between 18 and 80 years, and found that antibody responses were induced in all recipients. Participants aged 60 and over were slower to respond, taking 42 days before antibodies were detected in all recipients compared with 28 days for participants aged 18-59, the researchers said.
Antibody levels were also lower in those aged 60-80 years compared with those aged 18-59, they said. The BBIBP-CorV vaccine used in the study is based on a sample of the virus that was isolated from a patient in China.
Stocks of the virus were grown in the lab using cell lines and then inactivated using a chemical called beta-proprionolactone. BBIBP-CorV includes the killed virus mixed with another component, aluminium hydroxide, which is called an adjuvant because it is known to boost immune responses.
The trial was not designed to assess efficacy of the vaccine, so it is not possible to say whether the antibody responses induced by the vaccine, called BBIBP-CorV, are sufficient to protect from SARS-CoV-2 infection, according to the researchers. "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," said Professor Xiaoming Yang, one of the authors of the study, from the Beijing Institute of Biological Products Company Limited.
"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," said Yang.
There are currently 42 vaccines for COVID-19 in clinical trials, the researchers noted. These vary in type and include DNA plasmid vaccines, inactivated virus vaccines, adenovirus-vectored vaccines, RNA vaccines, protein subunit vaccines and virus-like particle vaccines, they said.
Some of these have already been shown to be safe and to elicit immune responses in early phase clinical trials. The first phase of the study involved 96 healthy volunteers aged between 18 and 59 years and a second group of 96 participants aged between 60 years and 80 years.
Within each group, the vaccine was tested at three different dose levels, with two vaccinations administered on day 0 and 28. A fourth group within each age group were given two doses of a placebo vaccine. In the second phase of the study, 448 participants aged between 18 and 59 years were randomly assigned to receive either one 8 microgramme shot of vaccine or placebo, or two shots of 4 microgramme vaccine or placebo.
No serious adverse events were reported within 28 days of the final vaccination, and the most common side effect was pain at the injection site, the researchers said. There were no instances of clinically significant changes in organ functions detected in laboratory tests in any of the groups, they said.
The greatest antibody responses were elicited by two 4 microgramme doses of the vaccine at either days 0 and 21 or 0 and 28, according to the resaerchers. "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. This provides useful information for a phase 3 trial, Yang said.
The researchers noted some limitations with the study, including the short duration of follow up at just 42 days. They also highlighted that the study did not include children and adolescents aged under 18.
" More studies are needed to establish whether the inactivated SARS-CoV-2 vaccines are capable of inducing and maintaining virus-specific T-cell responses," said Professor Larisa Rudenko from the Institute of Experimental Medicine, Russia, who was not involved in the study.
This is because CD4-positive T-cell help is important for optimal antibody responses, as well as for cytotoxic CD8-positive T-cell activation, which, in turn, are crucial for viral clearance if neutralising antibody-mediated protection is incomplete, Rudenko said.
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