Much of the problem has been the slowness of Sinopharm and Sinovac to publish full data, while trials held abroad have shown very mixed results. For Sinopharm, the World Health Organization quoted an efficacy rate of 79 percent for preventing both symptomatic disease and hospital admissions. In the first respect that would put it on a par with AstraZeneca. In the latter respect it is rather below the performance of the western vaccines so far approved for use. As for Sinovac, results have been all over the place. Brazilian trials at first suggested an efficacy against symptomatic illness of 78 percent — hastily downgraded to just 50.4 percent when mild cases were added. That is only just over the 50 percent threshold that the WHO, and many countries, demand for approval. Other trials have produced better outcomes: interim results from a Turkish study claimed 91 percent efficacy and a study involving Indonesian healthcare workers 65 percent. Why are these results so different? One possibility is that different trials are using different standards to define symptomatic disease. Another is that production of the Sinovac vaccine itself is not constant: that different batches have very different results. That is one problem with producing dead-virus vaccines: the process of inactivating the live virus, either chemically or through the application of heat, can change the way the body reacts to it. But with a lack of good data from the company itself it is hard to tell. The biggest blot against Sinovac remains the real-world data from Chile.