Behind a paywall...Chinese Covid-19 Vaccine Far Less Effective Than Initially Touted in Brazil
China’s effort to boost its image by providing Covid-19 vaccines to the developing world suffered a setback after one of its leading inoculation candidates turned out to be 50% effective in late-stage trials in Brazil, significantly lower than earlier results showed.
Brazil’s Butantan Institute, a São Paulo-based public institute that is the first to complete late-stage trials of the CoronaVac vaccine, had said last week that it was shown to be 78% effective and offer total protection against severe cases of the disease.
But after rising pressure from Brazilian scientists, some of whom accused the trial’s organizers of misleading the public, Butantan said Tuesday those rates only included volunteers who suffered mild to severe cases of Covid-19. When data from all volunteers was considered—including those who contracted “very mild” cases of Covid-19 and required no medical assistance—the total efficacy rate fell to 50.4%, Butantan said.
Sinovac didn’t respond to requests for comment.
Sinovac and Butantan had initially scheduled to reveal the efficacy rate by Dec. 15 but delayed it a week, citing a decision to collect additional data. A week later, the announcement was delayed again, which Brazilian researchers attributed to Sinovac’s request for more time to consolidate data from trials in Indonesia and Turkey.
“It’s extremely unusual, I’ve never seen this,” said Denise Garrett, an epidemiologist at the Washington-based Sabin Vaccine Institute who worked for the Centers for Disease Control and Prevention in Atlanta for more than 20 years. “They had already delayed the results—it seems they found them to be unsatisfactory so they came up with a way to announce the results in a more favorable way,” she said.
The problem for Sinovac's CoronaVac is that it elicits poor neutralizing antibody levels (about 1/3 as much as for Covaxin/AztraZeneca). By simple inference, it was never going to produce a 90-95% efficacy rate. It didn't really need to- just needed to be cheap, effective enough (>50% efficacy is still the threshold for CDC/EMA/WHO) demonstrated by trusted
data, to be a sensible option for many countries. Moreover, the Brazilian data is likely very close to its 'true' efficacy, since there are 15K trial participants there (by far, the biggest proportion of their Phase 3 study enrollment), not a bunch of small 1-2K participant cohorts (in multiple other countries, i.e., Turkey/Indonesia, etc.) amalgamated together. Because there would never be trial enrollment/conduct discrepancies amongst countries, right? It's a bad look, but probably nothing new for the CCP.
AztraZeneca's selective breast-beating debate of 90% vs 62% efficacy is much less egregious (no hiding of data). And may be there's a lesson to be learned for DCGI and Bharat Biotech as well. Sloppy statements such as 'clinical trial mode' without further explanation doesn't cut it anymore in a world of 'transparency'- more nuanced messaging is needed. Inoculate small numbers of people if you must. Better yet, purchase those vials (if one wishes to support the home team), sit on them a bit until BB's Phase 3 interim data analysis comes out, and then when there is reasonable efficacy demonstrated, proceed with mass vaccinations. This might be close to the actual plan, given the limited initial GOI purchasing data in the public domain.
A 50-70% efficacy target is a reasonable neighborhood for this class of (inactivated) vaccines. Not a highly immunogenic mRNA vaccine (with huge neutralizing antibody levels), but as mentioned previously, likely confers more broad-spectrum protection against mutations because of the multiple antigenic targets (against which the host can produce antibodies) presented by a whole virion.