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Modelling direct and herd protection effects of vaccination against the SARS-CoV-2 Delta variant in Australia.
Med J Aust. 2021 11 01; 215(9):427-432.MJ

Abstract

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 (R eff v ¯) 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 R eff v ¯ = 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 R eff v ¯ = 3, the mixed program could achieve herd protection at 60-70% population coverage and without vaccinating 5-15-year-old children. At R eff v ¯ = 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 R eff v ¯ declines and vaccination coverage increases. Assuming the most plausible R eff v ¯ 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.

Authors+Show Affiliations

Australian Institute of Tropical Health and Medicine, James Cook University, Townsville, QLD.Australian Institute of Tropical Health and Medicine, James Cook University, Townsville, QLD.Australian Institute of Tropical Health and Medicine, James Cook University, Townsville, QLD. University of Hawai'i at Mānoa, Honolulu, HI, United States of America.Australian Institute of Tropical Health and Medicine, James Cook University, Townsville, QLD. Australian Department of Defence, Melbourne, VIC.Australian Institute of Tropical Health and Medicine, James Cook University, Townsville, QLD.Australian Institute of Tropical Health and Medicine, James Cook University, Townsville, QLD. University of Rajshahi, Rajshahi, Bangladesh.Monash University, Melbourne, VIC.Monash University, Melbourne, VIC.Monash University, Melbourne, VIC.Biological Data Sciences Institute, Australian National University, Canberra, ACT.

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

Language

eng

PubMed ID

34477236

Citation

McBryde, Emma S., et al. "Modelling Direct and Herd Protection Effects of Vaccination Against the SARS-CoV-2 Delta Variant in Australia." The Medical Journal of Australia, vol. 215, no. 9, 2021, pp. 427-432.
McBryde ES, Meehan MT, Caldwell JM, et al. Modelling direct and herd protection effects of vaccination against the SARS-CoV-2 Delta variant in Australia. Med J Aust. 2021;215(9):427-432.
McBryde, E. S., Meehan, M. T., Caldwell, J. M., Adekunle, A. I., Ogunlade, S. T., Kuddus, M. A., Ragonnet, R., Jayasundara, P., Trauer, J. M., & Cope, R. C. (2021). Modelling direct and herd protection effects of vaccination against the SARS-CoV-2 Delta variant in Australia. The Medical Journal of Australia, 215(9), 427-432. https://doi.org/10.5694/mja2.51263
McBryde ES, et al. Modelling Direct and Herd Protection Effects of Vaccination Against the SARS-CoV-2 Delta Variant in Australia. Med J Aust. 2021 11 1;215(9):427-432. PubMed PMID: 34477236.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Modelling direct and herd protection effects of vaccination against the SARS-CoV-2 Delta variant in Australia. AU - McBryde,Emma S, AU - Meehan,Michael T, AU - Caldwell,Jamie M, AU - Adekunle,Adeshina I, AU - Ogunlade,Samson T, AU - Kuddus,Md Abdul, AU - Ragonnet,Romain, AU - Jayasundara,Pavithra, AU - Trauer,James M, AU - Cope,Robert C, Y1 - 2021/10/11/ PY - 2021/08/24/revised PY - 2021/07/16/received PY - 2021/08/25/accepted PY - 2021/9/4/pubmed PY - 2021/11/10/medline PY - 2021/9/3/entrez KW - COVID-19 KW - Epidemics KW - Epidemiologic measurements KW - Health policy KW - Infectious diseases KW - Nonlinear dynamics KW - Vaccine preventable disease SP - 427 EP - 432 JF - The Medical journal of Australia JO - Med J Aust VL - 215 IS - 9 N2 - 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 (R eff v ¯) 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 R eff v ¯ = 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 R eff v ¯ = 3, the mixed program could achieve herd protection at 60-70% population coverage and without vaccinating 5-15-year-old children. At R eff v ¯ = 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 R eff v ¯ declines and vaccination coverage increases. Assuming the most plausible R eff v ¯ 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. SN - 1326-5377 UR - https://www.unboundmedicine.com/medline/citation/34477236/Modelling_direct_and_herd_protection_effects_of_vaccination_against_the_SARS_CoV_2_Delta_variant_in_Australia_ L2 - https://doi.org/10.5694/mja2.51263 DB - PRIME DP - Unbound Medicine ER -