Chinese Communists say their 2nd vaccine candidate made from inactivated Covid-19 virus needs two doses 21 days apart to get peak antibody levels. People over 60 years old make less antibodies may not reach peak antibodies for 48+ days
The latest study 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. Antibody levels were also lower in those aged 60-80 years compared with those aged 18-59 (Mean neutralising antibody titre 42 days after receiving a 8μg vaccine dose was 228.7 for people aged 18-59, and 170.9 for those aged 60-80).
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.
Professor Xiaoming Yang, one of the authors of the study, from the Beijing Institute of Biological Products Company Limited, Beijing, China, 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."
There are currently 42 vaccines for COVID-19 in clinical trials. 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. Some of these have already been shown to be safe and to elicit immune responses in early phase clinical trials.
The BBIBP-CorV vaccine used in the study reported here 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.
