As the World Health Organisation puts it, “No substantive data are available related to impact of [the AstraZeneca vaccine] on transmission or viral shedding”. Or other vaccines.
There are theoretical reasons to hope that the vaccines reduce transmission a fair bit. Getting to know definitely will be difficult. Solid studies of transmission require good knowledge about where each new infected person got the virus.
That’s why we still don’t know how much less never-symptomatic people transmit than eventually-symptomatic ones, and how small a factor transmission via surfaces is, rather than through particles in the air (probably much smaller than first thought, but…)
Meanwhile there is agitation for “vaccine passports” and the like. It lacks scientific grounding.
As Zack Muddle (letters, Solidarity 581) says, the scientists’ committee which decided the vaccination schedule in Britain included health and care workers alongside the old and vulnerable in the priority groups. Health and care workers face much more risk than other occupational groups.
The committee cited a secondary argument, as Zack quotes: “Even a small reduction in transmission arising from vaccination would add to the benefits” here, because health and care workers are also at more risk of transmitting to the old and vulnerable.
Note: even, small, would, add to… The scientists recognise they don’t know about reduction in transmission.
Probably by the time two-dose vaccination of groups prioritised for their risk of Covid death or severe illness is complete (a way off yet) we will know more about transmission, and that can be factored into later prioritisation. We don’t know yet.
Martin Thomas, Islington