The data presented so far only relate to prevention of disease “of any severity”.  We know that the other Covid-19 vaccines (and this is generally true for vaccines) are more effective at preventing more severe outcomes.  And most people – particularly younger people (and only an eighth of the study population was aged >60 years) – who are infected have relatively mild disease.  This means that it is likely that the efficacy of this vaccine against severe illness – hospital admission, critical care needs (ICU admission), and death will be higher, possibly considerably higher than the efficacy against “disease of any severity”.

While the study was undertaken at a time and in populations in which a number of virus variants were circulating, I note that a relatively small proportion of the cases that arose were of the Beta (South African, B.1.351) or Delta (Indian, B.1.617.2) variants.  These two variants have shown the most “vaccine escape” so far, although other vaccines remain effective after two doses.  As the Delta variant – which appears to be considerably more transmissible – becomes more prevalent, it will be important to know if this vaccine is effective at preventing this variant.

I would be wary of being too dismissive of this vaccine based on the very limited information provided to date.

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