The data comes from a phase 1/2 trial with the CoronaVac vaccine.
CoronaVac, an investigational COVID-19 vaccine, was shown to be both safe and induced an immune response in a recent study.
The data comes from it randomized controlled phase 1/2 trial, and the findings were published in The Lancet Infectious Diseases.
The CoronaVac vaccine was developed by Chinese company Sinovac, and based on inactivated SARS-CoV-2 virus.
“Our findings show that CoronaVac is capable of inducing a quick antibody response within four weeks of immunization by giving two doses of the vaccine at a 14 day interval,” Fengcai Zhu, professor and joint lead author of the study, from the Jiangsu Provincial Center for Disease Control and Prevention, Nanjing, China, said. “We believe that this makes the vaccine suitable for emergency use during the pandemic. In the longer term, when the risk of COVID-19 is lower, our findings suggest that giving two doses with a one month interval, rather than a two week interval, might be more appropriate for inducing stronger and potentially longer-lasting immune responses. However, further studies are needed to check how long the antibody response remains after either vaccination schedule.”
The phase 1/2 clinical trial was conducted in China with trial participants who were healthy and ages 18 to 59. The participants did not have any symptoms of COVID-19 and have not traveled to areas where there were high incidence rates of the virus.
One hundred and forty-four participants were enrolled in April. Participants were split into 2 groups to receive either 2 injections given 14 days apart or 2 injections given 28 days apart.
“Within each of the two groups, participants were randomly assigned to receive either a low dose of the vaccine (3µg, 24 participants), a high dose (6µg, 24 participants) or placebo (24 participants),” according to the investigators. “In total, in this first phase, 96 participants received two doses of CoronaVac and 47 received the placebo (one participant withdrew from the placebo group). Antibody levels were checked 14 days and 28 days after the final immunization.”
After each vaccination, for 7 days, participants recorded side effects they experienced including pain or redness at the injection site, or body-wide symptoms such as fever or cough. Serious adverse events were collected throughout the study and until 6 months after the last dose.
Just 1 participant suffered a of severe adverse event within 48 hours of receiving the first dose in the 6µg group. Investigators This was considered to be possibly related to vaccination. The participant quickly recovered—within three days—and did not experience a similar reaction after the second vaccine.
Phase 2 of the trial was initiated when all participants in phase 1 had finished a 7-day observation period after their first dose. They enrolled 600 participants in this study in May. The investigators again used the same dosing criteria.
“Overall, the researchers found the 0 and 28 schedule induced the strongest antibody responses (Mean neutralizing antibody titers 28 days after final immunization: Day 0 and 14 schedule: 3 µg, 23.8; 6 µg, 30.1; Day 0 and 28 schedule: 3 µg, 44.1; 6 µg, 65.4),” the investigators reported. “However, even at the highest levels, antibodies induced by the CoronaVac vaccine candidate were lower than those that have been observed in patients who have recovered from COVID-19 (Mean neutralizing antibody titers: CoronaVac, 65.4; COVID-19 patients, 163.7).”
There are additional trials being conducted in Indonesia, Turkey, and Brazil. In Brazil the trial was briefly paused due to a report of an adverse event, but has since resumed.
“CoronaVac is one of many COVID-19 vaccine candidates that are being explored in parallel,” Gang Zeng, PhD, one of the authors of the study, said. “There are a multitude of different vaccine technologies under investigation, each with their own advantages and disadvantages. 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. The vaccine may also remain stable for up to three years in storage, which would offer some advantages for distribution to regions where access to refrigeration is challenging. However, data from phase 3 studies will be crucial before any recommendations about the potential uses of CoronaVac can be made.”