An interim analysis of the phase 3 control trial has proven the CoronaVac COVID-19 vaccine to be safe and effective at preventing infection.
The findings, published in The Lancet and presented at this year’s European Congress of Clinical Microbiology & Infectious Diseases (ECCMID), indicate that two doses of the CoronaVac vaccine offer 83.5% protection against symptomatic COVID-19. Amongst the more than 10,000 trial participants in Turkey, no adverse events or deaths were reported. Most of the side effects reported were mild and occurred within seven days of the vaccination.
Approved for emergency use in 22 countries
Developed by Sinovac Life Sciences, CoronaVac uses an inactivated whole virus. The vaccine encourages the immune system to attack the harmless form of the virus by producing antibodies to fight it off, leading to immunity. It has been approved for emergency use in 22 countries and has been in phase 3 trials since the middle of 2020 in Brazil, Indonesia, Chile, and Turkey.
Lead author Professor Murat Akova, from Hacettepe University Medical School, Turkey, said: “In order to bring the COVID-19 pandemic under control, the world needs every single dose of safe and effective vaccines, and our results add important evidence of the safety and effectiveness of inactivated-virus vaccines. One of the advantages of CoronaVac is that it does not need to be frozen, making it easier to transport and distribute. This could be particularly important for global distribution, as some countries may struggle to store large amounts of vaccine at very low temperatures.”
In the trial, participants were given two 3μg doses of CoronaVac 14 days apart. Between September 14 2020 and January 5 2021, 10,218 adults aged between 18 and 59 years old were randomly assigned to receive two doses of the vaccine (6,650) or a placebo (3,568). The trial was conducted across 24 centres in Turkey. The average age of the participants was 45 years old and 5,907 (58%) were male.
Following their first dose, 87 participants in the vaccine group and 98 in the placebo group were excluded for reasons such as returning a positive COVID-19 test. The most common reasons in the placebo arm were unblinding before the second dose and returning a positive COVID-19 test. A further four participants in the vaccine group were excluded after the second dose as they were aged over 59 years. In total, 10,029 participants (6,559 in the vaccine group and 3,470 in the placebo group) were included in the efficacy analysis, and 10,214 participants were included in the safety analysis.
Over 80% effective
A total of 150 COVID-19 cases were confirmed by PCR after an average follow-up of 43 days, an incidence rate of 123 cases per 1,000 people per year. From 14 days after the second dose, nine cases of symptomatic COVID-19 were confirmed in the vaccine group, an incidence rate of 32 cases per 1,000 people per year. In the placebo group, 32 cases were reported, an incidence rate of 192 cases per 1,000 people per year. Following careful analysis, the authors estimate that this is equivalent to a vaccine efficacy of 83.5%.
To evaluate the immune response induced by the vaccine, the researchers looked at a sample of 1,413 participants (981 from the vaccine group and 432 from the placebo group). CoronaVac induced an antibody response among 90% of those who received the vaccine, with antibody response decreasing with increasing age in men and women.
Mild and few adverse reactions
Adverse reactions were analysed using data from 10,214 participants (6,646 in the vaccine group and 3,568 in the placebo group). The incidence of adverse events in those who received the vaccine was relatively low at 19%. The incidence in the placebo group was 17%.
A total of 3,845 adverse effects were reported in 1,862 participants. Most of the reported adverse effects (90%) were mild, and included fatigue, pain at the injection site, and myalgia. No severe adverse events or fatalities were recorded during the study period, and only six participants in the vaccine group and one in the placebo group were withdrawn from the study due to adverse events. Only one adverse event, an allergic reaction, required hospitalisation.
Further research required
Though these results are significant, the authors acknowledge that the analysis only looked at a short follow-up period and involved a relatively young and low-risk population. Researchers say that further data is needed on the duration of protection, and the safety and efficacy of the vaccine in elderly people, adolescents, young children, and those with chronic diseases. Data on the effectiveness of CoronaVac against variants of concern is also required. Study participants received doses 14 days apart, whereas community immunisation has involved a 28-day interval. While it has been claimed that 28-day immunisation schemes lead to better immunogenicity, the longer the interval, the higher the chances of contracting COVID-19 before getting fully immunised.
The phase 3 trial results follow an earlier phase 1/2 trial that reported on the safety and immunogenicity of CoronaVac in healthy children and adolescents.