key: cord-1022291-s43wbg7t authors: Watson, L. M. title: Likelihood of infecting or getting infected with COVID-19 as a function of vaccination status, as investigated with a stochastic model for New Zealand (Aotearoa) date: 2021-11-29 journal: nan DOI: 10.1101/2021.11.28.21266967 sha: 7d8764788770584823307c10b3e55c0c59f53708 doc_id: 1022291 cord_uid: s43wbg7t Aim: The New Zealand government is transitioning from the Alert Level framework, which relies on government action and population level controls, to the COVID-19 Protection Framework, which relies on vaccination rates and allows for greater freedoms (for the vaccinated). As restrictions are eased, there is significant interest in understanding the relative risk of spreading COVID-19 posed by unvaccinated and vaccinated individuals. Methods: A stochastic branching process model is used to simulate the spread of COVID-19 for outbreaks seeded by unvaccinated or vaccinated individuals. The likelihood of infecting or getting infected with COVID-19 is calculated based on vaccination status. Results: A vaccinated traveler infected with COVID-19 is 9x less likely to seed an outbreak than an unvaccinated traveler infected with COVID-19. For a vaccination rate of 50%, unvaccinated individuals are responsible for 87% of all infections whereas 3% of infections are from vaccinated to vaccinated. When normalized by population, a vaccinated individual is 6.8x more likely to be infected by an unvaccinated individual than by a vaccinated individual. For a total population vaccination rate of 78.7%, which is equivalent to the 90% vaccination target for the eligible population (over 12 years old), this means that vaccinated individuals are 1.9x more likely to be infected by an unvaccinated individual than by a vaccinated, even though there are 3.7x more vaccinated individuals in the population. Conclusions: This work demonstrates that most new infections are caused by unvaccinated individuals. These simulations illustrate the importance of vaccination in stopping individuals from becoming infected with COVID-19 and in preventing onward transmission. Results: A vaccinated traveler infected with COVID-19 is 9x less likely to seed an outbreak than an 23 unvaccinated traveler infected with COVID-19. For a vaccination rate of 50%, unvaccinated individuals 24 are responsible for 87% of all infections whereas 3% of infections are from vaccinated to vaccinated. When normalized by population, a vaccinated individual is 6.8x more likely to be infected by an . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint The copyright holder for this this version posted November 29, 2021. ; https://doi.org/10.1101/2021.11.28.21266967 doi: medRxiv preprint NOTE: This preprint reports new research that has not been certified by peer review and should not be used to guide clinical practice. there is only a 6% chance. This is because the vaccine is assumed to be 50% effective at preventing 131 onward transmission. 7,13 For an unvaccinated seed infection, there is a 54% chance that the outbreak has 132 up to 151 infections after 31 days. 134 Figure 1 shows the importance of vaccination in stopping outbreaks from being seeded. A vaccinated 135 traveler is 9x less likely to seed an outbreak in a community than an unvaccinated traveler (note that this 136 . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this this version posted November 29, 2021. ; https://doi.org/10.1101/2021.11.28.21266967 doi: medRxiv preprint model does not account for the protection provided by testing requirements prior to traveling, which 137 would reduce the risk factor posed by unvaccinated travelers). This illustrates the importance that 138 travelers are vaccinated (or tested prior to travelling, or both), especially if travelling from regions with 139 significant COVID-19 community transmission (e.g., Auckland) to regions with low vaccination rates 140 (e.g., Northland). Continued community testing (not modeled here) is required to rapidly identify any 141 outbreaks that are seeded before they grow. . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint The copyright holder for this this version posted November 29, 2021. ; https://doi.org/10.1101/2021.11.28.21266967 doi: medRxiv preprint CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint The copyright holder for this this version posted November 29, 2021. ; https://doi.org/10.1101/2021.11.28.21266967 doi: medRxiv preprint COVID-19 Vaccine Data. 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JAMMI Crisanti 263 A; Imperial College COVID-19 Response Team International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint The copyright holder for this this version posted ENE-COVID): a nationwide, population-based seroepidemiological 268 study Modelling to support a future COVID-19 strategy for Aotearoa 270 Te Pūnaha Matatini Children are unlikely to be the main drivers of the COVID-19 pandemic -a 272 systematic review The role of children in the spread of COVID-19: using 274 household data from Bnei Brak, Israel, to estimate the relative susceptibility and infectivity in 275 children Maori and Pacific people in New Zealand have a higher . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprintThe copyright holder for this this version posted November 29, 2021. ; https://doi.org/10.1101/2021.11.28.21266967 doi: medRxiv preprint