Based on current work (BMC Infectious Diseases https://doi.org/10.1186/s12879-020-05737-6 , Preprint https://doi.org/10.1101/2021.03.10.21253251 ), a model-based assessment of the effect of natural and vaccine immunization is updated monthly and made publicly available. This makes it possible to classify the already effective reduction of the propagation dynamics through this aspect.
As of August 1, 2021 an adapted chart is introduced. It takes into account the waning of immunity of recovered persons. It can be seen by the drop of the blue curves (immune by past un-/detected infection) from April 2021. This effect is compensated by the start of the vaccination program (incl. recovered persons), which are shown by the green curves.
By September 1, 2021 percentages for vaccination effectiveness and the average duration for waning of immunity after recovery were updated with new data. The prior was slightly lowered, the latter was increased from 150 days to 300 days.
By 1 September 2021, approximately 51% of the Austrian population had been immunised. Of these, the vast majority (approx. 35 percentage points) are now vaccinated persons (incl. vaccinated recovered persons). Only about 6 percentage points now have their immunity solely due to having recovered from a SARS-CoV-2 infection. This leads to a reduction of the effective reproduction number by approx. 39% compared to a fully susceptible population (or the current effective reproduction number would be more than 64% higher with a fully susceptible population).
The following graph, an enlargement of the blue and dark green curves from the figure above, illustrates the decline in immunity due to recovery:
The decline in the recovered-only immune population from April 2021 is very clear here. Plotted with the dashed lines are the total numbers of COVID-19 infected (proven cases below; unreported cases above). Due to the loss of immunity after 300 days (= 10*30 days), the number of immunized population decreases noticeably each 10 months after the start of an epidemic wave.
Comparisons with the estimates from 1 August 2021 (see below) are not fully legitimate since parameters for vaccinations and waning of immunity were updated.
To model the occurrence of the contribution of the effect of vaccination: percentage values of efficacy as well as duration of delay of the effect influence the modelled immunisation of the population. The assumptions are summarised here: see Picture For more information on vaccination modelling, please refer to the COVID-TAV project (https://www.dwh.at/news/covid-19-entscheidungsgrundlage-fur-gezielte-impfstrategien-vorgestellt/, https://www.umit-tirol.at/page.cfm?vpath=departments/public_health/tavcovid19&switchLocale=de_AT), for more information.
Funded by the Austrian Research Promotion Agency (FFG) COVID-19 Emergency Call, the Vienna Science and Technology Fund WWTF-COVID-19 Rapid Response Funding, the Medical Scientific Fund of the Mayor of the City of Vienna