Read on Twitter
As overall infection was reduced, this would suggest that the AZ vaccine does reduce infectiousness so some degree. But even if all adults were vaccinated, it probably wouldn't achieve herd immunity.
In the Moderna vaccine study they only did asymptomatic swabs routinely before the second dose and found a lower number of asymptomatic infections in the vaccine group (14/14134) than in the control group (38/14073)
https://www.fda.gov/media/144453/download
https://www.fda.gov/media/144453/download
In the Pfizer vaccine study, they are planning to do N serology to see if participants get asymptomatic infection, but the results aren't available yet.
https://pfe-pfizercom-d8-prod.s3.amazonaws.com/2020-09/C4591001_Clinical_Protocol.pdf
https://pfe-pfizercom-d8-prod.s3.amazonaws.com/2020-09/C4591001_Clinical_Protocol.pdf
So, these vaccines prevent disease, and some may reduce infectiousness to an uncertain and varying degree. This is not unlike the flu vaccine - it reduces infection by about 50% but we don't get herd immunity.
But there is still benefit in getting a vaccine that protects you, even if it may not block transmission. Getting the vaccine means that you have a reduced risk of getting sick.
Australia has access to 10 million doses of the Pfizer vaccine that is being delivered over the year. We also have access to 53 million doses of the AstraZeneca vaccine (3.8 million doses available soon, and roughly 1 million doses a week). https://www.health.gov.au/initiatives-and-programs/covid-19-vaccines/about-covid-19-vaccines/australias-vaccine-agreements
We also may have some more doses of different vaccines via the COVAX facility. There is also another vaccine that is under development (Novovax) but the phase 3 studies have only just commenced https://www.nih.gov/news-events/news-releases/phase-3-trial-novavax-investigational-covid-19-vaccine-opens
The Pfizer vaccine looks about as good as it gets - it appears to reduce symptomatic infection by about 95%, even if we don't know yet whether it reduces asymptomatic infection
But we if only used this vaccine, we could only vaccinate 5 million people (~20% of the population) over the next year. This wouldn't achieve herd immunity even if it completely prevented infection and infectiousness (which we don't know yet).
The AZ vaccine may not be as good (it reduces infection by about 62-70%) but this can be rolled out more quickly. Even if doesn't protect against transmission, it does protect against disease and that's a benefit.
The choice we have isn't whether to use one vaccine or the other. Our choice is whether to offer everything we have now to protect as many people as we can, or to leave some effective vaccines in the warehouse.
That said, I understand that there are ongoing discussions with vaccine manufacturers. But if you were in charge of a vaccine manufacturer, would you send your supply to a country where there are thousands of deaths a day or to Australia?
