[14] In Brazil, after 75% of the population in Serrana, São Paulo, received CoronaVac, preliminary results show deaths fell by 95%, hospitalizations by 86%, and symptomatic cases by 80%.

[15][16] In Indonesia, real-world data from 128,290 healthcare workers showed 94% protection against symptomatic infection by the vaccine, beating results in clinical trials.

[17] Phase III results from Turkey, published in The Lancet, showed an efficacy of 84% based on 10,218 participants in the trials.

Three doses of CoronaVac, however, did not provide adequate levels of protective antibodies by the same measure,[42] in direct contradiction to claims made by the vaccine manufacturer.

[49] After 75% of the adult population received the vaccine, preliminary results show deaths fell by 95%, hospitalizations by 86% and symptomatic cases by 80%.

According to Ricardo Palacios, a director at São Paulo's Instituto Butantan, "The most important result was understanding that we can control the pandemic even without vaccinating the entire population.

"[50][51] In July 2021, researchers from the Chilean Ministry of Health published a paper containing real-world data for their vaccination campaign.

[68] The study also found that effectiveness against symptomatic disease decreased with increasing age: Preliminary data from a large effectiveness study in Brazil with 61 million individuals from 18 January to 30 June 2021, when the Gamma variant was dominant in the country, indicate that effectiveness is markedly reduced in those aged 90 or older, attributable to immunosenescence:[65] On 21 October 2021, the WHO recommended a third dose as part of the initial course for older adults 3–6 months after the second dose and for immunocompromised individuals 1–3 months after the second dose because these groups mount a weaker immune response compared to healthy adults.

[13] CoronaVac could remain stable for up to three years in storage, which might offer some advantage in vaccine distribution to regions where cold chains are not developed.

[71] In November 2020, Brazil's Instituto Butantan began building a facility to manufacture 100 million doses of CoronaVac a year, with a target completion date in September 2021.

[72] On 10 December, São Paulo Governor João Doria said that in the interim, prior to the local manufacture of CoronaVac, Instituto Butantan aimed to fill and finish 1 million doses of the vaccine per day.

[75] In May 2021, Hungary announced an agreement to fill and finish CoronaVac, with the goal to eventually manufacture it locally in a new plant in Debrecen.

[81] In July 2020, Sinovac began Phase III trials to evaluate efficacy and safety on 9,000 volunteer healthcare professionals in Brazil, collaborating with Butantan Institute.

[82][83] On 19 October, São Paulo Governor João Doria said the first results of the clinical study conducted in Brazil proved that among the vaccines being tested in the country, CoronaVac is the safest, the one with the best and most promising immunization rates.

[94] In July, Sinovac began Phase III trials in Chile with 14,000 participants for children and adolescents and expand from 6 months to 17 years old.

[96] On 1 April 2021, a preliminary report[97] from a phase III clinical trial in Chile[98] revealed that CoronaVac is safe and induces humoral and cell-mediated immunity in adults (18–59 years old) and the elderly (60 years or older) similar to previous phase II trials conducted in China with the same age groups and immunization schedule consisting of two doses with a 14-day interval.

A robust increase of T helper cells (CD4+) secreting interferon gamma was detected 14 days after both doses in response to stimulation with peptides of the S protein and of other viral particles, but the response to S protein peptides was reduced in the elderly due to a natural reduction of activated CD4+ T cells in this age group, as found in studies of other vaccines.

[99][100] Ricardo Palácios, medical director of Brazil's Instituto Butantan, said Sinovac's relatively low efficacy rate of 50% was due to more rigorous standards for what counted as an infection among trial participants.

[99][100] Possible explanations for lower efficacy rate included: trial was largely made up of frontline health care workers who were more exposed to the virus;[100] two vaccine doses were given at shorter intervals (2 weeks);[100][102] counting very mild cases;[100][103] and the Gamma variant (lineage P.1), more transmissible and perhaps evaded immunity better, was circulating.

[103] According to Instituto Butantan director Dimas Covas, the Brazilian group was considered more vulnerable to infection and exposure to higher viral loads.

[105] Preliminary results from a large study of health care workers suggest one dose of CoronaVac is still about 50% effective against symptomatic COVID-19 in Manaus.

[106] In June, Thailand's Public Health Ministry stated the vaccine had 71%-91% efficacy against infection by the Alpha strain.

[107] In June 2021, Reuters reported that more than 350 Indonesian doctors and medical workers out of 5,000 in Kudus contracted the Delta strain despite being vaccinated with the CoronaVac, an infection rate of 7%.

[19] In late August 2020, China approved CoronaVac for emergency use to vaccinate high-risk groups such as medical staff.

[127] Turkey approved emergency use on 13 January[128] and President Recep Tayyip Erdoğan received his first dose at Ankara City Hospital.

[133] Indonesia approved emergency use authorization on 11 January[134] and President Joko Widodo received the first shot of the vaccine.

The immunization campaign was initially focused on teachers, health professionals, firefighters, police, and military personnel.

"[204] Earlier in February 2022, health authorities refused to disclose data on which COVID-19 vaccine had been taken by Omicron patients, claiming the information "was not readily available.

However, CoronaVac's limited effectiveness compared to the BioNTech vaccine, along with the zero-COVID strategy, have been regarded as factors behind Hong Kong's spiking cases as of March 2022.

[207] A political showdown began in October 2020, when Bolsonaro vetoed a deal between the Brazilian health ministry and the São Paulo government for the purchase of 46 million doses of the vaccine.