NZ modelling shows boosters dampen Omicron transmission

Embargoed until: Publicly released: 2022-04-01 00:01

New Zealand

New Covid-19 modelling suggests booster shots make a big difference to the spread of Omicron. In a modelling scenario reflecting NZ's vaccination rates, the boosted population is 5x larger than the number of unvaccinated individuals, but is predicted to get only 2.1x as many infections, and to pass on just 1.6x as many infections – far less than the 5x as many that would be expected if the vaccine did not offer any protection. A separate model evenly divided the population between unvaccinated, double-vaccinated, and boosted people, and found that unvaccinated people were responsible for 45% of Omicron infections compared to 39% for double-vaccinated, and 15% for those who are boosted. NB: This summary was updated on 30 March.

Media release

From: New Zealand Medical Association (NZMA)

I use a mathematical model to simulate the spread of COVID-19 and track the vaccination status of who causes each infection and who is infected. This provides useful information that cannot be determined from real-world data because, as the numbers of cases has increased, contact tracers are overwhelmed.

Most new infections are caused by unvaccinated individuals (when normalized by population). For Delta, unvaccinated individuals cause 87% of all new infections whereas transmission between vaccinated individuals (two doses) makes up only 3% of infections. For Omicron, unvaccinated individuals cause 45% of all new infections, vaccinated (two doses) cause 39%, and boosted (three doses) cause only 15%. Transmission between boosted individuals is only 3%, indicating that three doses of the vaccine are effective at preventing infection and transmission.

Journal/
conference: New Zealand Medical Journal

Organisation/s: University of Canterbury

Funder: N/A

Media Contact/s

Contact details are only visible to registered journalists.