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Sinovac Vaccine Falls Short of Expectations, But Options Limited

Steve Baragona

   "Better than nothing."

   That's one infectious disease expert's assessment of Sinovac Biotech's
   COVID-19 vaccine,following reports that hundreds of Indonesian health
   care workers whohadreceived the vaccine caught the disease anyway.

   At least 10 doctors have diedafter getting both doses of Sinovac's
   CoronaVac vaccine, according to the Indonesian Medical Association.

   It's unclear how widespread these "breakthrough" infections are. It's
   also not clear how severe most of the infections are.Little
   peer-reviewed dataon the vaccineareavailable.

   What information is available suggeststhatthe vaccine is less potent
   than others, especially against the highly contagious delta variantthat
   was first detected in India.

   However, access to more effective vaccines is limited in much of the
   world, experts note. Indonesia is one of dozens of countries where the
   Chinese company's vaccine makes up a substantial part of the available
   doses.

   While the shortage of published peer-reviewed data makes it hard to
   evaluate the vaccine, a few available studies provide a glimpse.

   The government of Uruguay [1]released data earlier this month showing
   CoronaVac reduced COVID-19 infections by 61%, hospitalizations by 92%
   and deaths by 95%.

   Although notpeer-reviewed, the study isone ofafew
   thatcompareCoronaVacwithanother vaccine.
   FILE - Empty vials to be filled with the Pfizer/BioNTech vaccine are
   seen at a production facility in Reinbek, near Hamburg, Germany, April
   30, 2021.

   Pfizer-BioNTech
   The Pfizer-BioNTech shot performed better against infections in general
   in the study, lowering rates by 78%. But hospitalizations and deaths
   were about the same.

   It's not clear what the dominant variant was during the study, however.

   A key measure of vaccine potency is the level of neutralizing
   antibodies--the proteins the immune system produces thatpreventthe
   virus from infecting cells.

   The Pfizer and Moderna vaccines produce very high levels of these
   antibodies,which help maintain protection againstvariants,saidPeter
   Hotez, dean of the National School of Tropical Medicine and a professor
   at the Baylor College of Medicine.

   "Yes, you're getting some breakthrough infections with the delta
   variant, but they tend not to be serious infections," he said. "People
   aren't being hospitalized or losing their lives because of COVID-19."

   "When you look at some of the data on the Sinovac vaccine," he added,
   "the levels of virus-neutralizing antibody, even after two doses, can
   still be quite low."

   The Sinovac vaccine produced lower levels of these antibodies than
   seven other vaccines, including those from Pfizer, Moderna, University
   of Oxford-AstraZeneca and Johnson & Johnson, according to a study in
   the journal[2]Nature Medicine.

   The antibody response is even less effective against the delta variant,
   which has exploded in Indonesia and many parts of the world.

   It's not clear, however, exactly what that decline means for patients.
   The vaccine still offers protection against the most serious forms of
   the disease, a Chinese official told state media.

   In China's first delta outbreak, in Guangdong province earlier this
   month, "none of those vaccinated infections became severe cases, and
   none of the severe cases were vaccinated," said Feng Zijian, former
   deputy director at the Chinese Center for Disease Control and
   Prevention.

   Meanwhile, supplies of other vaccines are arriving slowly in much of
   the world.

   "Sometimes,that's all people have access to," Hotez said. "It's better
   than nothing."

References

   1. https://www.gub.uy/ministerio-salud-publica/comunicacion/noticias/segundo-estudio-efectividad-vacunacion-anti-sars-cov-2-uruguay-8-junio-202
   2. https://www.nature.com/articles/s41591-021-01377-8#MOESM1

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