RIO DE JANEIRO (BLOOMBERG) - A study of a small Brazilian town vaccinated with the shot made by Sinovac Biotech showed it can control Covid-19 outbreaks more effectively than expected from clinical testing, giving another boost to the Chinese-made inoculation that is relied on by dozens of developing countries.
While neighbouring cities were being hit hard by the pandemic, Serrana - a town of 45,000 people where the study was carried out by the Sao Paulo state government - saw deaths fall by 95 per cent in the five weeks right after the mass vaccination was completed.
Symptomatic cases dropped by 80 per cent and hospitalisations decreased by 86 per cent.
About 75 per cent of the town's residents were fully vaccinated; of the target adult population, 95 per cent came forward to receive both doses.
No severe side effects from the vaccine were reported and there were no Covid-related deaths among participants 14 days after the second dose was applied.
The area around Serrana, some 315km from Sao Paulo, was overrun by the P1 variant during the study, affirming the jab's effectiveness against the strain first found in Brazil, said Dr Ricardo Palacios, research director at Butantan Institute.
"Now we can say that it's possible to control the pandemic with vaccines," he said, adding that Covid-19 numbers also fell for children.
The Serrana study may offer clues for other developing nations on how much of the public needs to be vaccinated in order to begin moving past the pandemic that continues to wreak havoc in Latin America and beyond.
It is also the latest in a string of real-world evidence validating the controversial Chinese shot, which only just cleared the minimum 50 per cent efficacy threshold in clinical trials, the lowest among first-generation Covid-19 vaccines.
Sinovac, a Bejing-based company, has also been criticised for disclosing less trial and safety data than Western vaccine makers.
How well Sinovac's shot works is a high-stakes question for the developing world, which is largely reliant on the Chinese vaccine after rich countries snapped up the extraordinarily effective mRNA inoculations by Western companies BioNTech, Pfizer and Moderna.
The vaccine, called CoronaVac, is being used by several dozen places ranging from Hong Kong to Peru, and over 600 million doses have already been distributed. It also forms the backbone of the immunisation effort in China, where more than 20 million doses of six different vaccines are administered every day.
The study was led by the Butantan Institute, which produces CoronaVac in Brazil. Almost two-thirds of Serrana's inhabitants got the vaccine between February and April, with another third ineligible to receive the shot if they were under 18 years old or pregnant.
"This is the first study of its kind in the world," Butantan's director Dimas Covas said at a press conference on Monday (May 31). "This is primary data on the effects of vaccination in a population that will help the authorities to develop public policies."
The Chinese vaccine, made from the traditional method of injecting an inactivated form of the virus to stimulate immune response, came under intense international scrutiny and criticism early this year after the shot's clinical trials across Brazil, Turkey and Indonesia put the vaccine's efficacy anywhere between 50 per cent and over 90 per cent.
The company and its trial partners did not address the discrepancies, further fuelling doubt.
But data that is emerging from countries that widely deployed the shot in recent months has been broadly positive.
Last month, a study based on nearly 130,000 health workers in Indonesia's capital Jakarta shows the shot is 94 per cent effective against symptomatic infection, and slashes hospitalisation and death by 96 per cent and 98 per cent, respectively, rates comparable with mRNA vaccines.
It is still unknown how well the shot works to stop onward transmission, that is, whether it can also halt the spread of infection and not just sickness.
While infection rates improved after first doses were administered, Covid-19 was not properly controlled in Serrana until after a second shot was given. A complete study will be published soon.
That underlines the importance of people returning for a second shot. In Brazil, some 66 million vaccines have been administered, covering 21.4 per cent of the population with a single dose. About 10.5 per cent of the country is now considered to be fully inoculated, according to the Bloomberg vaccine tracker.
Despite the vaccine's widespread use around the world, it has yet to be granted emergency use listing from the World Health Organisation (WHO), the body's version of regulatory approval that has been given to Western vaccines and a similar shot from China's Sinopharm.
The international health agency's stamp of approval would enable the shot to be distributed even more widely through the Covax facility that aims to ensure access to safe and effective vaccines especially for poor countries.
WHO is seeking more data from the company on the shot's safety and manufacturing process, Dow Jones reported last week, citing people familiar with the matter.