Episode Details

Clear graphics from Italy, The decline of COVID-19 severity and lethality over two years of pandemic https://www.medrxiv.org/content/10.1101/2022.07.01.22277137v1 20 to 40-fold reductions during the period of dominance of Omicron compared to the initial acute phase. Phase 1, Ancestral Probability of hospitalization per infection of 5.4% Probability of ICU admission of 0.65% Probability of death of 2.2% Phase 5, Omicron Probability of hospitalization, 95.1% reduction in risk Probability of ICU admission, 97.3% reduction in risk Probability of death, 97.5% reduction in risk Using epidemiological and genomic surveillance data To estimate the number of daily infections in Italy in the first two years of pandemic. Attack rate Ascertainment of SARS-CoV-2 infections Phase 1 (ancestral) NPIs Attack rate 2.8% Phase 2 (ancestral) Less stringent NPIs Attack rate 11.4% Phase 3 Alpha variant Mid -February 2021 to early July 2021 Alpha infected about 10.1% of the Italian population Phase 4, Delta Second half of 2021 Progressive relaxation of NPIs Attack rate 17.3% Phase 5, Omicron End of December 2021 Attack rate, 51.1% of the Italian population became infected with Omicron Evolution of population susceptibility Percentage of the population susceptible to SARS-CoV-2 End of first phase, 97.5% February 20, 2022, 13% By February 20th, 2022 a marked proportion of individuals unprotected against SARS-CoV-2 infection can be found among vaccinated subjects, due to the waning of vaccine protection Evolution of COVID-19 severity and lethality Probability of hospitalisation Probability of ICU admission Probability of death Evolution of population susceptibility Natural, post infection immunity is now the main factor reducing population sensitivity Vaccination protection is seen to be declining Omicron natural infection had the largest protective effect Repeat exposure to omicron (and sub variants) is likely to have the same effect going forward. NPIs will reduce repeat exposures NPIs will reduce exposure to other respiratory viruses such as RSV

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