Vaccine CoronaVac has general efficacy of 50.38%

The rate is slightly above the 50% minimum required by WHO

Published in 13/01/2021 - 12:01 By Elaine Patricia Cruz - São Paulo

CoronaVac, the vaccine against the novel coronavirus manufactured by Butantan Institute in collaboration with Chinese pharmaceutical company Sinovac, has a general efficacy of 50.38%. The information was announced by the São Paulo state government on Tuesday (Jan. 12).

Last week, the government had said that the efficacy rate of the vaccine was 78 percent. But this refers only to light cases and those that require medical attention.

The results were observed in studies carried out in Brazil on health agents, who are more exposed to the virus. However, when light cases that demand no medical care whatsoever are taken into account, efficacy was lower. “Other studies, from other manufacturers, did not include cases with people who had a headache for two days, even with a positive RT-PCT outcome. But we did,” said Ricardo Palácios, medical director for clinical research with Butantan Institute.

In the testing phase, general efficacy is gauged by comparing the amount of all registered COVID-19 cases (light, moderate, and severe) between volunteers who were vaccinated and the volunteers that received the placebo.

Over the course of the efficacy study in Brazil, 252 volunteers experienced a light COVID-19 case (no need for medical assistance), 85 of whom had received the vaccine and 167 the placebo. Of all Brazilian volunteers, 4,653 were given the vaccine and 4,599 took the placebo. The result for the efficacy for light cases in patients who needed to receive some sort of medical assistance was 77.96 percent—a group within which seven had received the vaccine and 31 the placebo.

The efficacy of CoronaVac is above the minimum required by the World Health Organization (WHO) and by Brazil’s national sanitary regulator Anvisa. The recommended minimum efficacy for a vaccine is 50 percent. According to the São Paulo government, the efficacy rate was lower because it included all COVID-19 cases reported among volunteers, including light cases. “The vaccine is able to mitigate the intensity of the clinical disease in a high-exposure environment. This effect is higher the more [the severity of the disease] increases,” Palácios noted.

The vaccine ensured total protection against severe cases and deaths caused by the disease, Butantan stated. In these cases, the efficacy was a hundred percent. No volunteer that received the vaccine died or needed to be hospitalized.

The vaccine is stored at refrigerator temperature, between of the vaccine 2ºC and 8ºC. “We have today one of the world’s best vaccines—one of the vaccines with the easiest logistics because is transported in room temperature, is resistant outside of the refrigerator and may get to any city in the country,” said Butantan Director Dimas Covas.

Translation: Fabrício Ferreira -  Edition: Aline Leal / Nira Foster

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