13 October

The R number. Mentioned a lot in the pandemic, basically a measure of how much a virus spreads between people. There are two Rs - R0, and Re. R0 is how many people each person would infect if there was nothing to prevent the spread. Re is the spread once those preventions are in place. Anything above an R of 1 is exponential spread. For the flu, R0 is between 1 and 2. So if you catch flu, you’ll likely pass it on to only 1 or 2 other people. The R0 for Covid (Delta) is between 6 and 9. If you catch it, you’ll likely pass it on to 6-9 others. (Covid is nothing ‘like the flu’. The lockdowns smashed flu, with its puny R of 1-2. Covid is still going strong.) There’s an equation that lets you calculate Re, once you add vaccinations. Re = R0 x (1-X*Ve) X - proportion of people vaccinated Ve - efficacy of the vaccine you’re using. Let’s say Australia manages to get 90% of all people vaccinated. That will make X = 0.9. We’re using AZ and Pfizer which have different vaccine efficacy (Ve), AZ is about 60-70% (0.6-0.7), Pfizer is about 95% (0.95). So to average out across the country, let’s say 80%, or a Ve of 0.8. We’ll take the R0 of Delta to be 8 (it’s between 6 and 9) Plugging into the equation: Re = 8 x (1 - 0.9 x 0.8 ) = 2.24 So if Australia relies upon just vaccinations, which is the big push, each person who gets Covid will potentially still infect over 2 people. Exponential growth. (Covid is worse than the flu, even *after* vaccinations.) Even if you get 95% vaccine coverage, Re is still nearly 2. Vaccines won’t fix Covid for us. Not by themselves.