Sinovac’s COVID-19 vaccine CoronaVac has yielded some underwhelming clinical trial results, with a reported 50.4% efficacy rate according to new data from a Brazilian trial.
In the new Brazilian results, the vaccine was found to be just 50.4% effective at preventing symptomatic COVID-19 infections, only just meeting the World Health Organization’s (WHO) recommendation of at least 50% efficacy.
According to Reuters, officials from Brazil’s Butantan Institute announced last week that results showed a 78% clinical efficacy for CoronaVac against ‘mild-to-severe’ COVID-19 cases.
On Tuesday, Ricardo Palacios, medical director for clinical research at the Butantan Institute, said the new data, and respective efficacy rate, now also includes a group of ‘very mild’ COVID-19 infections observed in participants who received the vaccine.
In November 2020, Sinovac said that CoronaVac produced neutralising antibodies in an early-to-mid-stage trial, although the levels in the vaccinated group were lower than those observed in recovered COVID-19 patients.
The results from phase 1 and phase 2 trials, published in The Lancet Infectious Diseases, evaluated the CoronaVac vaccine in over 700 participants.
The primary immunogenic endpoint in the trials was the seroconversion of neutralising antibodies against the SARS-CoV-2 virus, which causes COVID-19. Seroconversion is defined as the time period during which antibodies develop and become detectable within the blood.
In the phase 2 trial, immune responses were ‘much better’ than those seen in the phase 1 trial, with seroconversion rates coming in at above 90% in both the 3μg and 6μg dose groups.
The researchers found that a more robust antibody response was generated and ‘longer persistence’ could be expected in the day 0 and 28 vaccination schedule compared to the day 0 and 14 schedule.
However, the study also found that the level of neutralising antibodies induced by the vaccine at day 28 was lower than that seen in patients who had recovered from COVID-19.
The researchers maintained that the vaccine could still provide ‘satisfying protection’ against COVID-19. This conclusion was based on researchers’ previous experience with other vaccines and preclinical data involving macaques.
Last month, researchers in Turkey said that the CoronaVac vaccine was 91.25% effective, according to an interim analysis.
Meanwhile, Indonesia granted Sinovac’s vaccine an emergency use approval earlier this week based on interim data in which CoronaVac demonstrated 65% efficacy.