This Snapshot article discusses the safety and side effects of CoronaVac, a COVID-19 vaccine that was recently validated by the World Health Organization (WHO) to protect against the SARS-CoV-2 virus.

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What do we know about Sinovac’s COVID-19 vaccine, CoronaVac?
Image credit: CHAIDEER MAHYUDDIN/Getty Images

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CoronaVac is a COVID-19 vaccine produced by Sinovac Biotech, a China-based pharmaceutical company with headquarters in Beijing. The company focuses specifically on the development and manufacturing of vaccines to target human infectious diseases.

This two-dose vaccine is recommended for individuals aged 18 years and above. It has an efficacy rate of 50.4% for preventing symptomatic infection, according to data from a Brazilian trial, and an effectiveness of 67%, according to a real-world study in Chile.

Sinovac’s vaccine was validated for Emergency Use Listing (EUL) by the WHO on June 1. WHO’s EUL procedure for CoronaVac included a review of the vaccine’s safety and efficacy, as well as “onsite inspections of the production facility.”

The Strategic Advisory Group of Experts on Immunization (SAGE), WHO’s main advisory board regarding vaccines, also reviewed the vaccine as part of WHO’s EUL validation.

As of January 2022, the vaccine is approved for use in 52 countries.

CoronaVac is an inactivated vaccine. It uses a dead version of the SARS-CoV-2 virus so that it cannot replicate, but it keeps the surface spike protein intact to trigger the body’s immune system to create antibodies for protection against the live virus, if it were to invade.

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Phase 1 and 2 clinical trial data for the vaccine, published in The Lancet in February 2021, reveal some of the side effects reported by trial participants.

According to the data, the most common side effect reported within 28 days of the second dose was injection-site pain (13–21%, depending on the dosing schedule). Injection site reactions are common with other COVID-19 vaccines, including the two inactivated COVID-19 vaccines by Sinopharm.

Other side effects included fatigue, diarrhea, and muscle pain. Most of these side effects were mild and lasted only for 2 days.

Additionally, the paper notes that participants who received CoronaVac reported a lower occurrence of fever in comparison to other COVID-19 vaccines, including the mRNA-based vaccine from Moderna and viral vector vaccines from Oxford-AstraZeneca and CanSino.

Similar to other COVID-19 vaccines approved by WHO, the global health agency recommends the CoronaVac vaccine for people with comorbidities, those who are immunocompromised, or those who previously have had COVID-19.

The WHO also recommends CoronaVac for people living with HIV. It states that while the trials reviewed by SAGE did not include this specific population, CoronaVac is a nonreplicating vaccine and can be recommended.

The WHO also notes that while this vaccine has not been sufficiently tested in pregnant people, its similarity to other vaccines deemed safe, such as those for hepatitis B, suggests that there are no expected concerns for the use of the vaccine during pregnancy.

Until studies have adequately evaluated the safety of CoronaVac in pregnant individuals, the WHO recommends its use when the benefits of vaccination outweigh the potential risks.

As with other authorized COVID-19 vaccines, individuals with a history of anaphylaxis to any of the vaccine’s ingredients should not receive the vaccine.

An article by the Global Times notes that, according to phase 2 clinical trials for the vaccine, a booster shot of CoronaVac after the initial two doses may boost antibody levels, with a tenfold increase in activity a week after the shot.

Sinovac plans to continue its clinical trials to determine the efficacy and timing of the booster shot, as well as the vaccine’s effectiveness against emerging SARS-CoV-2 variants.

Phase 3 clinical trial data for the vaccine will likely provide further insight into the efficacy and safety profile of the vaccine.

Since experts named Omicron a SARS-CoV-2 variant of concern, researchers have been looking into whether or not CoronaVac is effective against Omicron.

A paper published in Nature Medicine in January 2022 indicates that two doses of CoronaVac could not neutralize the Omicron variant.

“Notably, none of the individuals fully vaccinated with CoronaVac [whose data the study analyzed] had detectable neutralizing [antibodies] against [the] SARS-CoV-2 Omicron variant,” the paper authors write.

Adding a booster dose of the Pfizer-BioNTech mRNA vaccine somewhat improved the immune response to this variant. Still, participants had significantly reduced neutralization antibodies against Omicron compared with those produced against the Delta variant, suggesting a greater risk of vaccine breakthrough infections, the researchers warn.

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