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For the past year, we have been stuck in our homes, social distancing, wearing masks, and binge-watching every title on Netflix. Thankfully, vaccine technology has been developing at a rapid pace during the past few months. We now have multiple options to get immunized and save ourselves from anxiety and stress, one of which is the CoronaVac developed by the Chinese pharmaceutical firm SinoVac. Currently, this vaccine is being shipped around the world and used on millions of people. In order to ensure the safety of this vaccine, researchers in China conducted phase one and phase two trials (Wu et al. 2021). They monitored any adverse reactions in the participants through a 28-day period where the patients reached the desired seroconversion rate. The seroconversion rate is the amount of time it takes for antibodies to be produced and released into the blood. The study tests the hypothesis that the CoronaVac is safe and tolerated for people aged 60 years or more and it was published in the peer-reviewed medical journal The Lancet.

The CoronaVac vaccine is an inactivated vaccine. This means that in order to produce this vaccine, virus particles and other pathogens that cause disease have been killed. Once these dead particles are recognized by the immune system, antibodies are made to combat the live virus. Until now many vaccines like the Cholera vaccine or the Polio vaccine have been inactivated vaccines. With new technology, scientists are now able to easily produce mRNA vaccines that do not contain inactive virus molecules. Companies like Moderna and Pfizer resorted to using this new technology for the fight against COVID-19 (Miller 2020).

Countries other than China have also conducted their own research into the safety of the SinoVac. Notably, Brazil started its testing in late July (Pearson et al. 2021), one of the earliest countries outside of China to do so. The Brazilian study, however, conducted phase three trials which are different from the Chinese study. Moreover, Turkey, Bangladesh, Indonesia, and Saudi Arabia have also conducted their phase three trials.

This study was a randomized, double-blind clinical trial that was also placebo-controlled. The study took place in Renqui, China. The subjects were given either the vaccine or the placebo on day zero and day twenty-eight. Phase one was used to determine the best dose to be used for phase two. Phase two trials were used to determine the seroconversion rate of the vaccine. The researchers, monitored if any adverse effects of the vaccine appeared on the patients or not during this period.

The phase one clinical trials conducted between May 22 and June 1 of 2020 saw 72 people enter. First, the researchers assessed the safety of a low dose (3 µg) in a short seven-day period, then they repeated with a high dosage (6 µg).  Eleven days later, 350 people participated in phase two trials. During this trial, researchers have also tested a dose of 1.5 µg.  Thirty-nine of the 421 total participants reported slight or reasonable pain, the most common complaint was pain on the site of injection. The study also accounted for systemic effects like allergies and regularly monitored the patients on day eight, day fourteen, and day twenty-eight. The effects were assessed based on China National Medical Products Administration Guideline. All examinations were based on blood and urine samples collected from the patients.

The findings of this experiment suggest that the vaccine is safe for use in adults older than sixty. Although there was an instance that worried the researchers. One of the patients reported symptoms of pancreatitis in the 3 µg group but it was believed to be unrelated. In the past, some vaccines were linked to pancreatitis but those vaccines incorporated an aluminum adjuvant thought to provoke pancreatitis (Bizjak et al. 2017). This material was not present in the SinoVac. The difference in dose does not have a direct influence on the safety of the vaccine but the researchers have found that 1.5 µg dose has a relatively smaller response than 3 µg or 6 µg doses (Wu et al. 2021).

One of the most obvious critiques of the experiment is the diversity of the subjects. As stated by the researchers, this experiment has been conducted in a specific region in China and subjects were of Han ethnicity. This raises the question that whether genetic diversity can affect the outcomes of the study. The researchers have also noted that the long-term effects of the vaccine could not be evaluated at the time, but the trials would follow up for at least a year. Most importantly, the researchers have stated that the p values of the study were only present for reference and should be interpreted with caution. The p-value is a statistical term that determines the statistical significance of a study. Thus, the researchers are not certain of the statistical significance of this study.

In conclusion, these successful phase one and two trials make way for phase three trials to be conducted. Moreover, the results of a study like this can have great implications on vaccine development, government planning, economic planning, and the future plans of individuals. Finally, this research can alleviate some of the anxiety and doubts that people feel about the CoronaVac vaccine.



Wu Z, Hu Y, Xu M, Chen Z, Yang W, Jiang Z, Li M, Jin H, Cui G, Chen P, et al. 2021. Safety, tolerability, and immunogenicity of an inactivated SARS-CoV-2 vaccine (CoronaVac) in healthy adults aged 60 years and older: a randomized, double-blind, placebo-controlled, phase 1/2 clinical trial. The Lancet infectious diseases. doi:10.1016/S1473-3099(20)30987-7


Miller K. 2020 Dec 19 [accessed 2021 Feb 25]. What are the differences between the Pfizer and Moderna COVID-19 vaccines? Here’s what we know so far.

Pearson S, Magalhaes L, Deng C. 2021 Jan 7 [accessed 2021 Feb 25]. Sinovac’s covid-19 vaccine is 78% effective in Brazil late-stage trials. Wall Street Journal (Eastern ed.).


Bizjak M, Bruck O, Praprotnik S, Dahan S, Shoenfeld Y. 2017. Pancreatitis after human papillomavirus vaccination: a matter of molecular mimicry. Immunologic research.65(1):164–167.

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