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We are writing in response to the article published on Forbes online on 16th May by William Haseltine relating to the BioRxiv preprint publication ‘ChAdOx1 nCoV-19 vaccination prevents SARSCoV-2 pneumonia in rhesus macaques' by van Doremalen et al (2020).

The article compares vaccine research carried out in rhesus macaques by Sinovac Biotech in Beijing, China and at NIH, USA for The Jenner Institute at Oxford University, UK. These are small studies designed to look at the safety of the vaccine before starting human clinical trials. Head-to-head comparison of these studies are difficult since they differ in some important areas.    

There are a number of key aspects of the studies where the conclusions drawn by the author are incorrect and misleading:    

• Valid comparisons of virus levels post-challenge in nasal secretions cannot be made: these data are currently not available from the Sinovac group, where there was no intranasal challenge. The challenge protocols used differed between the two studies, in particular the dose and route of challenge used. The NIH study exposed the upper and lower respiratory tract to SARS-CoV-2 at a higher combined dose. The Sinovac study exposed the lower respiratory tract only and at a lower dose.    

• Virus neutralisation assays are notoriously lab-specific so, to compare titres, the samples should be assessed side by side in the same lab. However, the high neutralisation titres measured in the Sinovac study are from after the live virus challenge rather than after immunisation. Both of these studies show clear promise, with high efficacy in each case against lung disease, and research on both vaccines should continue as planned. So, the headline result is that the both vaccines were able to provide clear protection against lower respiratory tract infection in the respective models.    

Whilst legitimate to try to ask questions about the relative efficacy of the two vaccines, drawing comparative conclusions about the studies is flawed given the differences in study design. To draw definitive conclusions, one would have to compare the two vaccines side by side under the same experimental conditions. In the end it is the impact on clinical disease that matters. Of course with similar safety and efficacy the single dose Oxford vaccine, now partnered with AstraZeneca, would be preferred to a three dose vaccine for cost, manufacturing and operational reasons.    

As we write the clinical trials of these vaccines continue and we will soon have results giving us a better indication of the safety and potential efficacy of Oxford vaccine. The world needs multiple vaccines and it is our hope that of the many vaccines in development at least some will show promising efficacy and rapidly move to late-stage trials and subsequent approval as soon as possible    

Sarah Gilbert1, Neeltje van Doremalen2, Tonya Villafana3, Teresa Lambe1, Andrew Pollard1, Adrian Hill1, Mene Pangalos3, Vincent Munster2. 1University of Oxford, Oxford, UK; 2Rocky Mountain Labs, Montana, USA; 3AstraZeneca BioPharmaceuticals R&D, Royston, UK.