Modelling direct and herd protection effects of vaccination against the SARS-CoV-2 Delta variant in Australia

McBryde, Emma, Meehan, Michael T., Caldwell, Jamie M., Adekunle, Adeshina I., Ogunlade, Samson T., Kuddus, Md Abdul, Ragonnet, Romain, Jayasundara, Pavithra, Trauer, James M., and Cope, Robert C. (2021) Modelling direct and herd protection effects of vaccination against the SARS-CoV-2 Delta variant in Australia. Medical Journal of Australia, 215 (9). pp. 427-432.

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Objectives: To analyse the outcomes of COVID-19 vaccination by vaccine type, age group eligibility, vaccination strategy, and population coverage.

Design: Epidemiologic modelling to assess the final size of a COVID-19 epidemic in Australia, with vaccination program (Pfizer, AstraZeneca, mixed), vaccination strategy (vulnerable first, transmitters first, untargeted), age group eligibility threshold (5 or 15 years), population coverage, and pre-vaccination effective reproduction number (urn:x-wiley:1461023X:media:mja251263:mja251263-math-0002) for the SARS-CoV-2 Delta variant as factors.

Main outcome measures: Numbers of SARS-CoV-2 infections; cumulative hospitalisations, deaths, and years of life lost.

Results: Assuming urn:x-wiley:1461023X:media:mja251263:mja251263-math-0002 = 5, the current mixed vaccination program (vaccinating people aged 60 or more with the AstraZeneca vaccine and people under 60 with the Pfizer vaccine) will not achieve herd protection unless population vaccination coverage reaches 85% by lowering the vaccination eligibility age to 5 years. At urn:x-wiley:1461023X:media:mja251263:mja251263-math-0002 = 3, the mixed program could achieve herd protection at 60‒70% population coverage and without vaccinating 5‒15-year-old children. At urn:x-wiley:1461023X:media:mja251263:mja251263-math-0002 = 7, herd protection is unlikely to be achieved with currently available vaccines, but they would still reduce the number of COVID-19-related deaths by 85%.

Conclusion: Vaccinating vulnerable people first is the optimal policy when population vaccination coverage is low, but vaccinating more socially active people becomes more important as the urn:x-wiley:1461023X:media:mja251263:mja251263-math-0002 declines and vaccination coverage increases. Assuming the most plausible urn:x-wiley:1461023X:media:mja251263:mja251263-math-0002 of 5, vaccinating more than 85% of the population, including children, would be needed to achieve herd protection. Even without herd protection, vaccines are highly effective in reducing the number of deaths.

Item ID: 72742
Item Type: Article (Research - C1)
ISSN: 1326-5377
Keywords: Keywords: COVID-19; Epidemics; Epidemiologic measurements; Health policy; Infectious diseases; Nonlinear dynamics; Vaccine preventable disease.
Copyright Information: © 2021 AMPCo Pty Ltd
Funders: National Health and Medical Research Council (NHMRC), Australian Research Council (ARC)
Projects and Grants: NHMRC Investigator grant (1195102), NHMRC Early Career Fellowship (1142638), ARC Discovery Early Career Fellowship (210101344)
Date Deposited: 28 Mar 2022 22:56
FoR Codes: 42 HEALTH SCIENCES > 4202 Epidemiology > 420205 Epidemiological modelling @ 100%
SEO Codes: 20 HEALTH > 2002 Evaluation of health and support services > 200205 Health policy evaluation @ 100%
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