*Note: this paper is being presented at the European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) and is being published in The Lancet. Please credit both the congress and the journal in your stories*
A new study presented at this year's European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) and published in The Lancet, shows that the CoronaVac vaccine is safe and effective at preventing symptomatic COVID-19.
Interim results from a phase 3 trial in Turkey found the vaccine to offer 83.5% protection against symptomatic infections after two doses and be 100% effective against hospitalisation. Adverse effects were mainly mild and resolved within a day.
Vaccination is a crucial measure in breaking the transmission of COVID-19 infections. Thirteen vaccines in development, including CoronaVac, are inactivated vaccines. These contain virus particles that have been killed or altered and, while they can't cause disease, they can still provoke an immune response.
CoronaVac has been in phase 3 trials since mid-2020 in Brazil, Indonesia, Chile and Turkey and, as of April 28, 2021, had been approved in 22 countries for emergency use. Professor Murat Akova, Department of Infectious Diseases and Clinical Microbiology, Hacettepe University School of Medicine, Ankara, Turkey, and colleagues, studied the safety and efficacy of the vaccine in adults, including healthcare workers.
The double-blind randomised placebo-controlled phase 3 trial involved adults aged 18-59 who were enrolled at 24 centres in Turkey and randomised to receive two doses of CoronaVac, 14 days apart, or placebo. The median age was 45, 57.8% were male, 36% were healthcare workers and 15.6% were obese.
The primary outcome was the prevention of PCR-confirmed symptomatic COVID-19 at least 14 days after the second dose in 10,029 participants - 6,559 in the vaccine group and 3,470 in the placebo arm.
The follow-up time was a median of 43 days. This is shorter than planned because the vaccine was approved for emergency use in a national vaccination programme that started during the study. Consequently, the study's ethics committee decided it would be unethical to continue giving volunteers the placebo and offered them the vaccine instead.
There were 41 cases of symptomatic COVID-19 at least 14 days after the second dose of vaccine or placebo. Nine were in the vaccine group and 32 in the placebo group. This equates to an efficacy of 83.5% in preventing PCR-confirmed symptomatic COVID-19.
There were no fatal cases of COVID-19. There were six hospitalisations in the placebo group and none in the vaccine group, giving an efficacy of 100% for the prevention of COVID-19-related hospitalisation.
Adverse events were reported by 18.9% of the vaccine group and 16.9% of the placebo group. The majority (90.2%) were mild and resolved within a day. No potentially life-threatening adverse events related to vaccination were observed and only one adverse event, an allergic reaction, required hospitalisation.
Immunological assays were carried out on a subset of the study group. The analysis is ongoing but initial results show that 89.7% of vaccine recipients developed antibodies against the virus's spike protein.
The authors say: "The world needs every possible dose of any safe and effective vaccine against SARS-CoV-2.
"Our results show that CoronaVac has high efficacy against symptomatic SARS-CoV-2 infection and hospitalisation, along with a very good safety profile in a population aged 18-59 years.
"This analysis involved a young and low-risk population and a very short follow-up period and therefore further data is needed on the efficacy of duration of protection of the vaccine and to assess the safety and efficacy in older adult populations, adolescents, children and individuals with chronic diseases.
"Data is also needed on the efficacy of the vaccine against new variants of the virus."