How well does the Sinovac vaccine work against Covid-19? We take a look at the latest data

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  • The CoronaVac Covid vaccine by Sinovac is being tested in children and adolescents in South Africa.
  • Initial trial results were promising and showed it was highly protective against severe disease, hospitalisation and death.
  • Data on its effectiveness against the Delta variant is still lacking, but lab studies show that a booster shot may be needed.

Chinese company Sinovac has been given the go-ahead by the South African Health Products Regulatory Authority (Sahpra) to test its Covid-19 vaccine in children and adolescents in South Africa, as part of a global Phase 3 study, News24 reported on Friday.  

The two-dose vaccine, known as CoronaVac, has been granted emergency use approval in more than 40 countries. Around 1.8 billion doses of the vaccine were supplied globally, including China, by the end of August 2021, according to Sinovac. 

In South Africa, the jab received conditional approval from Sahpra in July 2021. It may only be administered to people aged 18 to 59, although it has not yet been rolled out to adults in the country. 

The vaccine is currently not recommended for people under 18 years of age, pending the results of further studies in this age group, the World Health Organization (WHO) stated in September 2021. 

We round-up what the latest research shows on how well it protects against hospitalisation and death, its safety profile, as well as side-effects seen in people who received the vaccine.

Type of vaccine technology used

The vaccine uses an inactivated-virus technology – in other words, it is a dead version of the SARS-CoV-2 virus. It, therefore, cannot replicate and cause Covid disease, but can still trigger the body's immune system to create antibodies and protect against the virus when encountered, Health24 previously reported.

Late-stage trials

CoronaVac was found to be 51% effective at preventing Covid infection in late-stage trials.  

While this figure is lower than that provided by some of the other Covid vaccines already listed by the WHO, the trials also suggested that the vaccine was 100% effective at preventing severe disease and hospitalisation, starting 14 days after receiving the second dose.

How well it protects against variants of concern

An observational study in healthcare workers in Brazil showed that it remained effective against the Gamma variant of concern (VOC), which accounted for the majority of cases in the country.  

A real-world study, published in July 2021, found that CoronaVac was highly protective against Covid-related hospitalisation (87.5%), ICU admission (90%) and death (86%) among fully vaccinated adults aged 16 years and older, Health24 reported.  

The results were based on data from Chile's vaccination programme, which launched in February 2021. The researchers evaluated the vaccine's effectiveness in approximately 10.2 million fully immunised Chileans. 

But these results were based on the vaccine's performance against the Gamma and Alpha variants. There is currently limited data on how well CoronaVac protects against the highly transmissible Delta variant, which is dominating Covid infections in SA and multiple other countries.

Booster doses show promise

In people who received the second dose of the CoronaVac vaccine, samples taken six months later showed that there were no neutralising antibody activities against Delta, a study posted in preprint server medRxiv in September 2021 revealed.  

The same study, which involved laboratory research, indicated that a booster dose of the vaccine reversed a decline in antibody levels against Delta, easing concerns about long-term immunity against the worrying variant.  

According to the paper, there was a 2.5-fold higher neutralising potency against Delta about one month after the third dose, compared with the level seen about one month after the second shot. This type of antibody plays a key role in preventing the coronavirus from infecting cells.  

The study was conducted by researchers from the Chinese Academy of Sciences, Fudan University, Sinovac, and other Chinese institutions.

The findings “rationalise the use of three-dose immunisation regimens for inactivated vaccines”, they wrote in their paper.

Several countries, which are administering the vaccine, have started to give booster shots to those who are fully vaccinated with CoronaVac.

100 million doses to be shipped

According to a separate Reuters report, 100 million doses of the vaccine are expected to be shipped by the end of September 2021, via the WHO's pandemic programme. Most of the doses will reach Africa and Asia.

Is it safe?

Clinical trial data for the vaccine was published in The Lancet in February 2021 and indicated the most commonly experienced side-effects within 28 days after vaccination in trial participants were pain at the injection site (arm), which are common with other Covid vaccines. 

Other mild side-effects reported include fatigue, diarrhoea and muscle pain. These generally lasted only around two days.

People over 60

A small number of participants in the CoronaVac trials were above 60 years of age, which means safety data is currently limited for this age group. However, the WHO stated that, despite this limited data, there are no theoretical reasons to believe that the vaccine would be less safe in older adults than in younger adults. Available data indicate that it is safe in older adults, it said.

Safe for breastfeeding mothers

The WHO recommends the use of CoronaVac in pregnant women "when the benefits of vaccination to the pregnant woman outweigh the potential risks". 

Research on the vaccine's safety and effectiveness in this group is ongoing, but since the type of vaccine technology used is commonly used in many other vaccines that has a well-documented safety profile, including in pregnant women, the effectiveness of CoronaVac in pregnant women is expected to be comparable to that observed in non-pregnant women of similar age, says the WHO.  

The WHO also recommends that breastfeeding women get the vaccine.

"WHO does not recommend discontinuing breastfeeding after vaccination," it says.

People with comorbidities

CoronaVac is safe for people with comorbidities, including obesity, cardiovascular disease, and respiratory disease. These groups have been shown to have an increased risk of severe Covid, should they contract the virus.

What about people with HIV, immunocompromised?

People with HIV and those who are immunocompromised are also at higher risk of severe Covid. Given that CoronaVac is a non-replicating vaccine and cannot cause disease, it is also recommended that these groups be vaccinated with this vaccine.

'Big role for CoronaVac to play'

The approval and rollout of Sinovac's jab have been said by some experts to be crucial in curbing the Covid pandemic. In an article for The Conversation, Michael Head, Senior Research Fellow in Global Health, University of Southampton, said: "The inactivated vaccine method is a much more well-established way of designing a vaccine. Inactivated vaccines are typically easy to manufacture at large scale and have an excellent safety record.

"While vaccine demand continues to greatly outstrip supply and there's huge inequity in the global vaccine rollout, there remains a big role for CoronaVac to play – even if it is slightly less effective than some other vaccines." 

*For more Covid-19 research, science, and news, click here. You can also sign up for our Daily Dose newsletter here.

READ | What we know about the CoronaVac Covid-19 vaccine

READ | Covid-19: Promising findings on CoronaVac in new study - but questions remain about Delta variant

READ | OPINION | CoronaVac vaccine: Its results are patchy, but the world can’t ignore its usefulness

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