As lockdowns ease in New South Wales, Victoria and the ACT, and people return to work and socialising, many of us will be mixing more with others, even though a section of the community is still unvaccinated.
Many vaccinated people are concerned about the prospect of mixing with unvaccinated people. This mixing might be travelling on trains or at the supermarket initially. But also at family gatherings, or, in NSW at least, at pubs and restaurants when restrictions ease further, slated for December 1.
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Some people are wondering, why would a vaccinated person care about the vaccine status of another person?
Briefly, it’s because vaccines reduce the probability of getting infected, which reduces the probability of a vaccinated person infecting someone else. And, despite vaccination providing excellent protection against severe disease, a small proportion of vaccinated people still require ICU care. Therefore, some vaccinated people may have a strong preference to mix primarily with other vaccinated people.
But what exactly is the risk of catching COVID from someone who’s unvaccinated?
What’s the relative risk?
Recent reports from the Victorian Department of Health find that unvaccinated people are 10 times more likely to contract COVID than vaccinated people.
We also know that vaccinated people are less likely to transmit the disease even if they become infected. The Doherty modelling from August puts the reduction at around 65 per cent, although more recent research has suggested a lower estimate for AstraZeneca. Hence for this thought experiment, we’ll take a lower value of 50 per cent.