Last weekend, the China surpassed the mark of one billion applied doses of its vaccines against the Covid-19. Most of them were developed by local companies Sinovac and Sinopharm.

WHO has "very low confidence" in data on side effects of Chinese Sinopharm vaccine
Sinopharm received World Health Organization approval for emergency use in May. Image: Steve Heap – Shutterstock

Another hundreds of millions of doses of these immunizers were sent to more than 80 countries around the world.

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Last month, Sinopharm received approval from the World Health Organization (WHO) for emergency use. This month, it was Sinovac's turn.

Vaccines from Sinopharm and Sinovac laboratories do not register significant reactions

Both are inactivated virus vaccines. That is, they are made from viral particles produced in a laboratory, which are then inactivated so that they cannot be able to infect the organism. Many other widely known vaccines use similar technology, including those for polio, hepatitis A, and flu.

The formulas are mixed with an adjuvant, which is a substance added to vaccines to stimulate a stronger immune response.

Both contain a series of proteins to which the immune system can respond by stimulating the production of Antibodies to fight Covid-19.

Neither vaccine has a high incidence of side effects. There were a very low number of adverse events identified overall, suggesting substantial underreporting of cases.

Once vaccines are approved and used in large populations, they are continually monitored for very rare side effects. No significant safety concerns were identified during the launch of Sinovac's immunizer in China or Brazil. The same was observed in Indonesia and Chile.

Sinovac vaccine has no record of significant adverse reactions. Image: Vladimka production – Shutterstock

For example, in China, there were only 49 cases of serious adverse reactions reported, after more than 35,8 million doses of Sinovac administered in the country.

Regarding Sinopharm's vaccine, only 79 people reported having had reactions, all mild, after 1,1 million doses given in China, rates much lower than the usual rates of adverse event reporting from other manufacturers after immunization.

Effectiveness of Chinese Vaccines

The overall effectiveness of Sinovac's immunizing agent in preventing symptomatic infection was 51% in Brazil, 67% in Chile, 65% in Indonesia and 84% in Turkey. Differences in results can be explained, for example, by the different variants circulating in each country at the time, as well as by differences in the populations included in the studies.

In relation to Sinopharm, the effectiveness was 78% in the United Arab Emirates, Bahrain, Egypt and Jordan combined.

As with all vaccines for which data are available, the effectiveness against the most serious outcomes is greatest. The effectiveness of Sinovac's formula against cases requiring hospitalization in Chile, Brazil and Turkey was 85%, 100% and 100%, respectively.

For Sinopharm's immunizing agent, the effectiveness against hospitalization was 79%.

Currently, there are no data on the efficacy of Sinopharm's immunizer against any variant of concern, despite its use in more than 50 countries. 

As for the Sinovac vaccine, the efficacy against symptomatic infection with the Alpha and Gamma variants in Chile was 67%.

In Brazil, with the circulation of the Gamma variant, a preprinted study suggested that the efficacy against symptomatic infection was 42%.

As with any vaccine, it is also necessary to understand the effectiveness of these formulas in the elderly, adolescents, pregnant women and immunocompromised groups, and how long the protection lasts.

Increase in cases in countries that received immunizations from China worries

However, it is worrying that there has been an increase in infections in some countries where these vaccines have been widely used.

For example, the Seychelles vaccinated 68% of their population with two doses of Sinopharm's vaccine and the rest with AstraZeneca's immunizer.

The Seychelles is an archipelago of 115 islands in the Indian Ocean, off the east coast of Africa. There, there has been a recent record of an increase in the number of Covid-19 cases, suggesting that the herd immunity threshold may not have been reached. The exact threshold for this is unknown, but it is influenced by variants in circulation, the number of people vaccinated and the effectiveness of the vaccines.

According to Medical Xpress, detailed epidemiological studies are needed to investigate the issue, but news suggests that 20% of hospitalized and 37% of new active cases are fully vaccinated.

Bahrain and the United Arab Emirates also achieved high vaccination coverage, predominantly with the Sinopharm vaccine. They have also experienced recent Covid-19 outbreaks and are offering a booster dose of Pfizer six months after two doses of the Chinese immunizer, believing it may not provide enough protection. However, there is no publicly available data to determine whether this combination schedule is safe and produces a protective immune response.

There is also concern about the increase in cases in Indonesia. Almost all healthcare professionals have been vaccinated with Sinovac's vaccine, but some are developing serious illnesses.

Chile also achieved high vaccination coverage, especially with Sinovac's formula. About 75% of the adult population received one dose and 58% two. Despite this, a current rise in infections and a consistent high number of deaths has led to a general blockade across the capital, Santiago. The spread may be related to the Gamma variant, which is more transmissible and appeared for the first time in Brazil.

However, in Serrana, a small town in the interior of São Paulo, with about 45 inhabitants, 95% of adults' very high vaccination coverage with Sinovac's vaccine, here called CoronaVac, supposedly reduced symptomatic infections in 80% and deaths at 95%.

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