Two new large studies of China's CoronaVac COVID-19 vaccine showed good efficacy against symptomatic infection and severe disease, albeit with lower efficacy than the two mRNA coronavirus vaccines currently in use.
Overall 83.5% efficacy against infection
Interim efficacy and safety results from a phase 3 trial in Turkey were published yesterday in The Lancet. A team led by researchers from Hacettepe University School of Medicine in Ankara randomly assigned either the inactivated whole-virion CoronaVac vaccine or a placebo to 10,214 healthcare and community volunteers aged 18 to 59 years at 24 centers from Sep 14, 2020, to Jan 5, 2021. Participants received two doses of the vaccine or placebo 14 days apart.
Phase 3 trials have been testing CoronaVac since mid-2020 in Brazil, Indonesia, Chile, and Turkey, the authors noted.
Over a median follow-up of 43 days in the Lancet study, 9 of 6,646 (0.14%) participants in the vaccine group and 32 of 3,568 (0.90%) in the placebo group had symptomatic COVID-19 at least 14 days after their second dose, for a vaccine efficacy of 83.5%.
No vaccinees were hospitalized, compared with six in the placebo group, for a vaccine efficacy against coronavirus-related hospitalization of 100%. While the analysis of immunologic tests done on a subset of participants is ongoing, early results show that 89.7% of vaccinees had antibodies against the coronavirus's spike protein.
Adverse events occurred in 18.9% of vaccinees and 16.9% in placebo recipients. No deaths or serious adverse effects were reported. The most common systemic reaction was fatigue (8.2% in the vaccine group, 7.0% in the placebo group), and the most common local reaction was injection-site pain (2.4% in vaccinees, 1.1% in placebo recipients).
Pros, cons of inactivated vaccines
Median participant age was 45 years, 57.8% were men, 36.0% were healthcare workers, and 15.6% were obese (body mass index, 30 kg/m2 or greater). High blood pressure was the most common underlying condition, affecting 11.8% of 6,217 participants who had available comorbidity data.
The authors noted that inactivated vaccines may offer the advantages of no virus replicability or transmissibility in recipients, and the generation of a wide range of humoral and cellular immune responses against epitopes, or the parts of antigens recognized by the immune system. Potential disadvantages are the need for adjuvants to boost the immune response, handling of large quantities of live virus, and the verification of the integrity of antigens or epitopes.
The World Health Organization (WHO) gave emergency use approval to the vaccine, which is also called Sinovac, on Jun 1, 2021.
In a Lancet press release, lead study author Murat Akova, MD, PhD, said that the world needs every single dose of safe, effective vaccines to bring the pandemic under control.
"Our results add important evidence of the safety and effectiveness of inactivated-virus vaccines," he said. "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."
More data on the way
In a commentary in the same journal, Maheshi Ramasamy, MD, DPhil, of the University of Oxford and Lucy Jessop, MBBChir, of the National Immunisation Office in Dublin, said that open access to data on vaccines yet to be adopted locally will help inform decisions by countries on whether to allow in travelers who have received those vaccines.
"The recent WHO recommendation for use of CoronaVac, which is currently approved in 32 countries, could also facilitate free, safe movement of vaccinated individuals," Ramasamy and Jessop wrote.
They also said they eagerly anticipate the results of ongoing effectiveness and immunogenicity studies. "More data are needed on its efficacy against emerging SARS-CoV-2 variants and on its duration of protection across different age groups and geographical settings and in the presence of comorbidities," they wrote.
Second study: 65.9% protective against infection
A real-world study, published earlier this week in the New England Journal of Medicine, involved testing nearly 10.2 million Chilean residents 16 years and older who either had received at least one dose of CoronaVac or were unvaccinated against COVID-19 from Feb 2 to May 1, 2021.
The team, led by researchers from the Chilean Ministry of Health, found an adjusted vaccine effectiveness against infection of 65.9% in participants who received two doses of CoronaVac at least 14 days before, with 87.5% protection against hospitalization, 90.3% effectiveness against intensive care unit (ICU) admission, and 86.3% effectiveness against coronavirus-related death.
Vaccine effectiveness in fully immunized participants 60 years or older was 66.6% against infection, 85.3% against hospitalization, 89.2% protective against ICU admission, and 86.5% effective against death.
In participants who had received only the first dose at least 14 days before, vaccine effectiveness was only 15.5% against infection, 37.4% effective against hospitalization, 44.7% effective against ICU admission, and 45.7% protective against COVID-19 death.
Among a subset of participants who had been tested for COVID-19 using polymerase chain reaction or antigen test during the analysis segment of the study, vaccination effectiveness was higher than when the whole cohort was included. Adjusted vaccine effectiveness among fully vaccinated participants in this group was 72.9% against infection, 89.2% against hospitalization, 91.6% against ICU admission, and 87.8% against death.
The authors said that the study results are consistent with those from phase 2 trials of CoronaVac and with preliminary efficacy data. "Overall, our results suggest that the CoronaVac vaccine had high effectiveness against severe disease, hospitalizations, and death, findings that underscore the potential of this vaccine to save lives and substantially reduce demands on the health care system," they wrote.
The researchers added that estimates of vaccine effectiveness against infection are critical because they "reflect real-world challenges, such as logistics, cold chains, vaccination schedules, and follow-up, and also involve more diverse populations than those selected in randomized clinical trials, such as older or immunocompromised persons or those with coexisting conditions."
