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How effective is the Sinovac vaccine?

COVID-19 antibodies from Sinovac may last about six months, according to a new study

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A medical worker gives a shot of the Sinovac COVID-19 vaccine.

In this July 14, 2021, file photo, a medical worker gives a shot of the Sinovac COVID-19 vaccine during a vaccination campaign in Tangerang, Indonesia.

Tatan Syuflana, Associated Press

New research on Sinovac vaccines has shown that antibodies decline below a key threshold six months after the second dose of the vaccination, reported Reuters. The same research also found a third Sinovac booster shot can provide a strong immune response.

  • The CoronaVac vaccine from Sinovac Biotech is a Chinese-made vaccine commonly referred to as Sinovac, reported The Conversation.
  • Sinovac is the dominant vaccine for Brazil, China, Indonesia and Chile, per Reuters.

While Sinovac has a mixed reputation, the vaccine remains a useful component of effectively responding to ongoing COVID-19 outbreaks, reported The Conversation.

Let’s unpack the situation.

How effective is China’s Sinovac vaccine?

The WHO approved Sinovac in June for emergency usage, per a news release on the organization's website.

  • Sinovac had a 51% efficacy against symptomatic cases of COVID-19, according to the WHO.
  • The vaccine also had a 100% efficacy against severe cases and hospitalization in the studied populations, per the WHO.

However, the uncertain question with Sinovac — and other COVID-19 vaccines — remained about the duration of immunization and the efficacy against more transmissible variants, reported The Global Times.

How long do antibodies last after a Sinovac vaccine dose?

Chinese researchers published a new Sinovac study on Sunday that has not yet been peer-reviewed, reported Reuters. The study found that COVID-19 preventing antibodies from the Sinovac vaccine declined below detectable thresholds for a majority of vaccinated individuals six months after their second dose.

  • Among those who had received two Sinovac doses two weeks apart, only 16.9% of participants still had a detectable level of antibodies six months later, per Reuters.
  • Among those who had received two Sinovac doses four weeks apart, 35.2% of participants still had a detectable level of COVID-19 antibodies six months later, per Reuters.

However, the study remains “​​unclear how the decrease in antibodies would affect the shot’s effectiveness,” according to Reuters. Scientists have not figured out the exact antibody threshold needed to prevent COVID-19.

  • “In the short-to-medium term, ensuring more people complete the current two-dose schedule of Sinovac’s vaccine should be the priority,” the study concluded per Reuters.

Can booster shots help?

A third Sinovac booster shot does help produce a strong immune response. The new study found that antibody concentrations increase between three- to five-fold with a booster shot, per The Global Times.

  • Multiple countries that used Sinovac to vaccinate their populations have already begun offering boost shots, reported the Deseret News.
  • These boosters include third dose of Sinovac or doses of a different non-Sinovac vaccine, depending on the country, per the Deseret News.

With COVID-19 cases rising worldwide and new more transmissible variants, “the world needs all the vaccines it can get,” reported The Conversation, “and we cannot afford to pick and choose between them. ... There remains a big role for CoronaVac to play — even if it is slightly less effective than some other vaccines.”