New Zealand delayed the introduction of the Omicron variant of SARS-CoV-2 into the community by the continued use of strict border controls through to January 2022.This allowed time for vaccination rates to increase a...New Zealand delayed the introduction of the Omicron variant of SARS-CoV-2 into the community by the continued use of strict border controls through to January 2022.This allowed time for vaccination rates to increase and the roll out of third doses of the vaccine(boosters)to begin.It also meant more data on the characteristics of Omicron became available prior to the first cases of community transmission.Here we present a mathematical model of an Omicron epidemic,incorporating the effects of the booster roll out and waning of vaccine-induced immunity,and based on estimates of vaccine effectiveness and disease severity from international data.The model considers differing levels of immunity against infection,severe illness and death,and ignores waning of infection-induced immunity.This model was used to provide an assessment of the potential impact of an Omicron wave in the New Zealand population,which helped inform government preparedness and response.At the time the modelling was carried out,the date of introduction of Omicron into the New Zealand community was unknown.We therefore simulated outbreaks with different start dates,as well as investigating different levels of booster uptake.We found that an outbreak starting on 1 February or 1 March led to a lower health burden than an outbreak starting on 1 January because of increased booster coverage,particularly in older age groups.We also found that outbreaks starting later in the year led to worse health outcomes than an outbreak starting on 1 March.This is because waning immunity in older groups started to outweigh the increased protection from higher booster coverage in younger groups.For an outbreak starting on 1 February and with high booster uptake,the number of occupied hospital beds in the model peaked between 800 and 3,300 depending on assumed transmission rates.We conclude that combining an accelerated booster programme with public health measures to flatten the curve are key to avoid overwhelming the healthcare system.展开更多
We couple a simple model of quarantine and testing strategies for international travellers with a model for transmission of SARS-CoV-2 in a partly vaccinated population.We use this model to estimate the risk of an inf...We couple a simple model of quarantine and testing strategies for international travellers with a model for transmission of SARS-CoV-2 in a partly vaccinated population.We use this model to estimate the risk of an infectious traveller causing a community outbreak under various border control strategies and different levels of vaccine coverage in the population.Results are calculated from N¼100,000 independent realisations of the stochastic model.We find that strategies that rely on home isolation are significantly higher risk than the current mandatory 14-day stay in government-managed isolation.Nevertheless,combinations of testing and home isolation can still reduce the risk of a community outbreak to around one outbreak per 100 infected travellers.We also find that,under some circumstances,using daily lateral flow tests or a combination of lateral flow tests and polymerase chain reaction(PCR)tests can reduce risk to a comparable or lower level than using PCR tests alone.Combined with controls on the number of travellers from countries with high prevalence of COVID-19,our results allow different options for managing the risk of COVID-19 at the border to be compared.This can be used to inform strategies for relaxing border controls in a phased way,while limiting the risk of community outbreaks as vaccine coverage increases.展开更多
文摘New Zealand delayed the introduction of the Omicron variant of SARS-CoV-2 into the community by the continued use of strict border controls through to January 2022.This allowed time for vaccination rates to increase and the roll out of third doses of the vaccine(boosters)to begin.It also meant more data on the characteristics of Omicron became available prior to the first cases of community transmission.Here we present a mathematical model of an Omicron epidemic,incorporating the effects of the booster roll out and waning of vaccine-induced immunity,and based on estimates of vaccine effectiveness and disease severity from international data.The model considers differing levels of immunity against infection,severe illness and death,and ignores waning of infection-induced immunity.This model was used to provide an assessment of the potential impact of an Omicron wave in the New Zealand population,which helped inform government preparedness and response.At the time the modelling was carried out,the date of introduction of Omicron into the New Zealand community was unknown.We therefore simulated outbreaks with different start dates,as well as investigating different levels of booster uptake.We found that an outbreak starting on 1 February or 1 March led to a lower health burden than an outbreak starting on 1 January because of increased booster coverage,particularly in older age groups.We also found that outbreaks starting later in the year led to worse health outcomes than an outbreak starting on 1 March.This is because waning immunity in older groups started to outweigh the increased protection from higher booster coverage in younger groups.For an outbreak starting on 1 February and with high booster uptake,the number of occupied hospital beds in the model peaked between 800 and 3,300 depending on assumed transmission rates.We conclude that combining an accelerated booster programme with public health measures to flatten the curve are key to avoid overwhelming the healthcare system.
文摘We couple a simple model of quarantine and testing strategies for international travellers with a model for transmission of SARS-CoV-2 in a partly vaccinated population.We use this model to estimate the risk of an infectious traveller causing a community outbreak under various border control strategies and different levels of vaccine coverage in the population.Results are calculated from N¼100,000 independent realisations of the stochastic model.We find that strategies that rely on home isolation are significantly higher risk than the current mandatory 14-day stay in government-managed isolation.Nevertheless,combinations of testing and home isolation can still reduce the risk of a community outbreak to around one outbreak per 100 infected travellers.We also find that,under some circumstances,using daily lateral flow tests or a combination of lateral flow tests and polymerase chain reaction(PCR)tests can reduce risk to a comparable or lower level than using PCR tests alone.Combined with controls on the number of travellers from countries with high prevalence of COVID-19,our results allow different options for managing the risk of COVID-19 at the border to be compared.This can be used to inform strategies for relaxing border controls in a phased way,while limiting the risk of community outbreaks as vaccine coverage increases.
