This piece at Forbes by Bill Haseltine has set off a lot of comment – it’s a look at the Oxford group’s vaccine candidate as compared to the SinoVac candidate, and you may recall (background here) that these are the two teams that have separately reported that their vaccines appear to protect rhesus monkeys from infection after exposure to the coronavirus. Haseltine has some criticisms of the Oxford data, and as you will see from that link to his name, his opinions deserve to be taken seriously. So what’s going on? Update: here’s the take on this at BioCentury.
Looking at the preprint on the Oxford results, Haseltine has a problem with the claim that the monkeys were protected from infection by a dose of ChAdOx1 nCoV-19. The key data are in the preprint’s Figure 3.
The Oxford team checked for viral RNA several different ways. One was using bronchoaveolar lavage (BAL fluid), a sampling technique that involves running a bronchoscope down into the lungs and washing out aveolar spaces – a pretty darn invasive assay, which is why you don’t hear about it all that much compared to the still-not-so-nonivasive nose swabs.
BAL fluid of the virus-exposed unvaccinated animals showed coronavirus genomic RNA throughout the study, and viral subgenomic RNA (more indicative of active replication) at days 3 and 5 after exposure. Meanwhile, the vaccinated animals showed the genomic RNA in only two monkeys, and no subgenomic RNA at all.
So far, so good. But both vaccinated and unvaccinated monkeys showed the same amount of viral genomic RNA from nose swab samples (Figure 3c). That’s the test that’s used out in the human population, and that means that the vaccinated animals would still be declared as positive for the coronavirus after being exposed to it.
And the other thing that Haseltine notes is that the amount (the “titer”, in the lingo) of neutralizing antibodies in the blood of the vaccinated animals does not appear to be that high. You’d like to be able to dilute the blood antibody samples down by hundreds of times or even a thousandfold and still see antiviral activity in an in vitro assay, but in the Oxford case the activity started disappearing at about fortyfold dilution (Figure 2b).