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For more than a year, the concept of herd immunity against COVID-19 has fuelled political and economic debate across the world. The idea: when a sufficient number of people achieve medically induced or natural immunity, we can all go about our business and even open up the borders.

Here’s a definition: herd immunity occurs when a large portion of a community (the herd) becomes immune to a disease, making the spread of disease from person to person unlikely. As a result, the whole community becomes protected — not just those who are immune.

But we now have an Australian contribution to the debate thanks to the newish boss of Virgin, Jayne Hrdlicka, the most senior business figure to make the case that borders need to open even if “some people may die”.

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So what might “Hrdlicka immunity” look like? Crikey asked economist Richard Holden to turn his mind to it.

Here’s what he came up with: “Hrdlicka immunity is defined as: Virgin Australia segments flow * (1-mRNA vaccination rate) * R0<1.”

 To spell out the idea in more detail:

  • Virgin Australia segments flow is the average number of Virgin flights per person
  • (1-mRNA vaccination rate) is the proportion of the population susceptible to infection since that proportion haven’t had Pfizer or Moderna vaccine. That assumes Pfizer/Moderna are 100% effective, which is close enough, and assumes AstraZeneca doesn’t help — which is not right but works as an implicit simplification
  • R0 is the basic reproduction number of the virus. We need that product to be less than 1 to achieve herd immunity.

Of course, as Holden notes, the gloss here is we are assuming that only people flying on Virgin might infect others or be infected with COVID-19. Which is obviously cute, if not a tad contrived.

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Peter Fray
Peter Fray
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