Sinovac Biotech's CoronaVac vaccine can produce antibody responses in two doses given 14 days apart over 28 days, British medical journal Lancet revealed in a new study.
Despite producing antibodies lower than levels in previous COVID-19 patients, researchers believe the CoronaVac vaccine may produce sufficient immunity against the disease compared with other vaccines, the study read.
Further phase 3 studies will be "crucial" to determine the full efficacy of the vaccine against SARS-CoV-2, the study said, adding that additional tests with other age groups and patients with pre-existing conditions would also need to be trialled.
“Our findings show that CoronaVac is capable of inducing a quick antibody response within four weeks of immunisation by giving two doses of the vaccine at a 14 day interval. We believe that this makes the vaccine suitable for emergency use during the pandemic," Professor Feng-Cai Zhu of the Jiangsu Provincial Centre for Disease Control and Prevention in Nanjing said.
CoronaVac Phase Trials Show Positive Results
The news comes as researchers trial CoronaVac along with dozens other candidates, with the first and second clinical trials taking place in Suining county in Jiangsu. 144 healthy volunteers took part in phase one trials from 16 to 25 April this year.
Two groups of 72 volunteers were randomly given low, high and placebo doses of the vaccine, with 96 receiving the former two doses of CoronaVac and 47 the latter, respectively.
All remaining candidates were monitored for antibody counts after 14 and 28 days of immunisation. Participants reported side effects with notes, with more severe symptoms monitored six months after the final dose.
Investigations found that boosted manufacturing processes led to a higher number of spike proteins on inactivated viruses in the vaccine, which are used to recognise COVID-19 and trigger an immune response.
According to the study, stronger antibody responses were produced with doses given on day 0 and 28 of the trial. Phase 2 trials did not assess T-cell responses but will be studied in ongoing phase 3 trials.
“CoronaVac could be an attractive option because it can be stored in a standard refrigerator between 2 and 8 degrees centigrade, which is typical for many existing vaccines including flu," Dr Gang Zeng of Sinovac Biotech in Beijing said.
CoronaVac can also remain stable for up to three years in storage, allowing vaccines to reach regions with limited access to refrigeration, Gang added.
But Dr Naor Bar-Zeev of Johns Hopkins University, who was not involved in the Lancet study, warned that results should be "interpreted with caution until phase 3 results are published".
The ongoing pandemic has seen numerous countries race for an effective vaccine against COVID-19, with Sinovac running phase 3 trials in Brazil, Indonesia and Turkey, Reuters reported.
Further vaccines from US phramaceutical giant Pfizer/ BioNTech and Moderna are under development, and Russia's Sputnik V vaccine has been considered for a United Nations list of emergency vaccines after meeting essential criteria.
According to Moscow, Russia's COVID-19 vaccine has shown 92 percent efficacy based on a 21-day evaluation.