As I'm desparately trying to get my lil country over its vaccine hesistancy 'hill' and to a helpful number, this is how I've found it easiest to explain:
1. Yes, two individual, equally symptomatic patients - one vaccinated and one not - have been shown to have similar viral loads of covid - hence could spread it equally. BUT
2. Vaccinated people are less likely to catch covid AND less likely to develop as serious symptoms.
3. To demonstrate, if a population of 20 people all got exposed, three scenarios (just using rough rates):
a. All 20 are unvaccinated, likelyhood of maybe 16 catching covid and showing symptoms - hence 16 vectors to spread.
b. 10 vax'd, 10 not: 3 vax'd catch and display symptoms, 8 non-vax'd catch and display symptoms - hence 11 vectors to spread.
c. All 20 are vaccianted: 6 catch it and display symptoms, so 6 vectors.
That's why it's important for individuals who only care about their own health to get vax'd (to reduce transmission in the community) and how breakthrough patients having similar viral loads does NOT mean vaccinated are less likely to catch and develop symptoms.
Some of the reporting on this has been woeful. And then bad headlines are used by the inexplicably evil anti-vaxxers to promote their bizarre, literally murderous agenda.