{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,5]],"date-time":"2026-02-05T08:22:15Z","timestamp":1770279735550,"version":"3.49.0"},"reference-count":34,"publisher":"MDPI AG","issue":"13","license":[{"start":{"date-parts":[[2022,7,4]],"date-time":"2022-07-04T00:00:00Z","timestamp":1656892800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Veneto Regional Authority","award":["DGR 1643 del 24\/11\/2020"],"award-info":[{"award-number":["DGR 1643 del 24\/11\/2020"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJERPH"],"abstract":"<jats:p>In December 2021\u2013January 2022 the Veneto region in Italy faced an unprecedented wave of SARS-CoV-2 infections, even though both the vaccine coverage and the number of previously infected individuals keep increasing. In this study we address the protection against the SARS-CoV-2 infection offered by natural immunity and a three-dose regimen through a retrospective study based on Veneto\u2019s regional databases. In particular, we compared these protection levels during two distinct periods respectively representative of the Delta (B.1.617.2) and the Omicron (B.1.1.529) variants, in order to investigate and quantify the immunological evasion, especially of the Omicron. For each period we compared the incidence rate of infection among the population with various immunological protections against SARS-CoV-2 and performed a multivariable proportional hazard Cox binomial regression to assess the effectiveness afforded by both forms of active immunization. We found out that a previous SARS-CoV-2 infection (irrespective of its timing) offers 85% (83\u201387%) and 36% (33\u201339%) protection against being reinfected by Delta and Omicron, respectively. In addition, we estimated the third dose to be more effective in both periods and to have a minor proportional loss of effectiveness due to the rise of the Omicron variant, with an afforded effectiveness against SARS-CoV-2 Delta and Omicron infection of 97% (96\u201397%) and 47% (45\u201348%), respectively. Our findings suggest that viral variant factors may affect any form of active immunization but that receiving a booster vaccination cycle is more effective and less variable than natural immunity in terms of afforded protection against SARS-CoV-2 infections.<\/jats:p>","DOI":"10.3390\/ijerph19138179","type":"journal-article","created":{"date-parts":[[2022,7,4]],"date-time":"2022-07-04T11:15:05Z","timestamp":1656933305000},"page":"8179","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":7,"title":["Differences in Immunological Evasion of the Delta (B.1.617.2) and Omicron (B.1.1.529) SARS-CoV-2 Variants: A Retrospective Study on the Veneto Region\u2019s Population"],"prefix":"10.3390","volume":"19","author":[{"given":"Silvia","family":"Cocchio","sequence":"first","affiliation":[{"name":"Department of Cardiac Thoracic and Vascular Sciences and Public Health, University of Padua, 35131 Padua, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6321-7272","authenticated-orcid":false,"given":"Federico","family":"Zabeo","sequence":"additional","affiliation":[{"name":"Department of Cardiac Thoracic and Vascular Sciences and Public Health, University of Padua, 35131 Padua, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Giacomo","family":"Facchin","sequence":"additional","affiliation":[{"name":"Department of Cardiac Thoracic and Vascular Sciences and Public Health, University of Padua, 35131 Padua, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Nicol\u00f2","family":"Piva","sequence":"additional","affiliation":[{"name":"Department of Cardiac Thoracic and Vascular Sciences and Public Health, University of Padua, 35131 Padua, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Giovanni","family":"Venturato","sequence":"additional","affiliation":[{"name":"Department of Cardiac Thoracic and Vascular Sciences and Public Health, University of Padua, 35131 Padua, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1028-8119","authenticated-orcid":false,"given":"Thomas","family":"Marcon","sequence":"additional","affiliation":[{"name":"Azienda Zero of Veneto Region, 35100 Padua, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2235-1325","authenticated-orcid":false,"given":"Mario","family":"Saia","sequence":"additional","affiliation":[{"name":"Azienda Zero of Veneto Region, 35100 Padua, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4917-404X","authenticated-orcid":false,"given":"Michele","family":"Tonon","sequence":"additional","affiliation":[{"name":"Regional Directorate of Prevention, Food Safety, Veterinary, Public Health\u2014Veneto Region, 30123 Venice, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Michele","family":"Mongillo","sequence":"additional","affiliation":[{"name":"Regional Directorate of Prevention, Food Safety, Veterinary, Public Health\u2014Veneto Region, 30123 Venice, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Filippo","family":"Da Re","sequence":"additional","affiliation":[{"name":"Regional Directorate of Prevention, Food Safety, Veterinary, Public Health\u2014Veneto Region, 30123 Venice, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Francesca","family":"Russo","sequence":"additional","affiliation":[{"name":"Regional Directorate of Prevention, Food Safety, Veterinary, Public Health\u2014Veneto Region, 30123 Venice, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6012-9453","authenticated-orcid":false,"given":"Vincenzo","family":"Baldo","sequence":"additional","affiliation":[{"name":"Department of Cardiac Thoracic and Vascular Sciences and Public Health, University of Padua, 35131 Padua, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2022,7,4]]},"reference":[{"key":"ref_1","unstructured":"Worldometer (2022, March 14). Information on COVID-19 Coronavirus Pandemic. Available online: https:\/\/www.worldometers.info\/coronavirus\/."},{"key":"ref_2","unstructured":"Italian Institute of Statistics (ISTAT) (2022, March 04). Population with Permanent Address in Veneto Region on 1 January 2021, Available online: http:\/\/dati.istat.it\/Index.aspx?QueryId=18549."},{"key":"ref_3","unstructured":"Italian Department of Civil Protection (2022, March 14). COVID-19 Italy\u2014Monitoring of the Situation. Available online: https:\/\/opendatadpc.maps.arcgis.com\/apps\/dashboards\/b0c68bce2cce478eaac82fe38d4138b1."},{"key":"ref_4","unstructured":"Italian Agency of Drugs (AIFA) (2022, March 14). Annual Report on the Safety of Anti-COVID-19 Vaccines, 27\/12\/2020\u201326\/12\/2021, Available online: https:\/\/www.aifa.gov.it\/documents\/20142\/1315190\/Rapporto_annuale_su_sicurezza_vaccini%20anti-COVID-19.pdf."},{"key":"ref_5","unstructured":"Italian Ministry of Health (2022, March 14). Vaccinations Web Portal. Legislative Archive, Available online: https:\/\/www.salute.gov.it\/portale\/vaccinazioni\/archivioNormativaVaccinazioni.jsp."},{"key":"ref_6","unstructured":"Veneto Region (2022, March 07). Veneto Region Web Portal. Anti-COVID-19 Vaccination Campaign. Available online: https:\/\/regione.veneto.it\/dati-vaccinazioni\/."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"e85","DOI":"10.1056\/NEJMoa2114228","article-title":"Waning Immunity after the BNT162b2 Vaccine in Israel","volume":"385","author":"Goldberg","year":"2021","journal-title":"N. Engl. J. Med."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1393","DOI":"10.1056\/NEJMoa2114255","article-title":"Protection of BNT162b2 Vaccine Booster against Covid-19 in Israel","volume":"385","author":"Goldberg","year":"2021","journal-title":"N. Engl. J. Med."},{"key":"ref_9","unstructured":"Italian Ministry of Health (2022, March 14). General Direction of Health Prevention. Preliminary Indications for the Administration of Additional and \u201cBooster\u201d Doses during the Anti-SARS-CoV-2\/COVID-19 Vaccination Campaign, Available online: https:\/\/www.trovanorme.salute.gov.it\/norme\/renderNormsanPdf?anno=2021&codLeg=82776&parte=1%20&serie=null."},{"key":"ref_10","unstructured":"Italian Ministry of Health (2022, March 04). Vaccinations Web Portal. Anti-COVID-19 Vaccination Strategy, Available online: https:\/\/www.salute.gov.it\/portale\/nuovocoronavirus\/dettaglioContenutiNuovoCoronavirus.jsp?lingua=italiano&id=5452&area=nuovoCoronavirus&menu=vuoto."},{"key":"ref_11","unstructured":"(2021, June 23). COVID-19 on the Veneto Region: Report. Coronavirus: Cases and Vaccines, 8 March 2022. Veronasera. Available online: https:\/\/www.veronasera.it\/attualita\/coronavirus-covid19-Veneto-Verona-dati-bollettino-casi-vaccino-8-marzo-2022.html."},{"key":"ref_12","unstructured":"Coronavirus Statistics (2022, March 04). Coronavirus Statistics on the Veneto Region. Available online: https:\/\/statistichecoronavirus.it\/coronavirus-italia\/coronavirus-veneto\/."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"1255","DOI":"10.12998\/wjcc.v10.i1.1","article-title":"Omicron variant (B.1.1.529) of SARS-CoV-2: Mutation, infectivity, transmission, and vaccine resistance","volume":"10","author":"Ren","year":"2022","journal-title":"World J. Clin. Cases"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"100","DOI":"10.1140\/epjp\/s13360-021-02321-y","article-title":"Omicron: A mysterious variant of concern","volume":"137","author":"Gowrisankar","year":"2022","journal-title":"Eur. Phys. J. Plus"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1532","DOI":"10.1056\/NEJMoa2119451","article-title":"COVID-19 Vaccine Effectiveness against the Omicron (B.1.1.529) Variant","volume":"386","author":"Andrews","year":"2022","journal-title":"N. Engl. J. Med."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"492","DOI":"10.1056\/NEJMc2119358","article-title":"Third BNT162b2 Vaccination Neutralization of SARS-CoV-2 Omicron Infection","volume":"386","author":"Nemet","year":"2022","journal-title":"N. Engl. J. Med."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1063","DOI":"10.1038\/s41591-022-01753-y","article-title":"Effectiveness of mRNA-1273 against SARS-CoV-2 Omicron and Delta variants","volume":"28","author":"Tseng","year":"2022","journal-title":"Nat. Med."},{"key":"ref_18","unstructured":"Italian Superior Institute of Health (ISS) (2022, March 14). Extended Report on COVID-19. COVID-19: Surveillance, Infections Impact and Vaccine Efficacy, 11\/03\/2022. Available online: https:\/\/www.epicentro.iss.it\/coronavirus\/bollettino\/Bollettino-sorveglianza-integrata-COVID-19_9-marzo-2022.pdf."},{"key":"ref_19","unstructured":"World Health Organization (WHO) (2022, March 16). Tracking SARS-CoV-2 Variants. Available online: https:\/\/www.who.int\/en\/activities\/tracking-SARS-CoV-2-variants."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"494","DOI":"10.1056\/NEJMc2119270","article-title":"Effectiveness of BNT162b2 Vaccine against Omicron Variant in South Africa","volume":"386","author":"Collie","year":"2022","journal-title":"N. Engl. J. Med."},{"key":"ref_21","doi-asserted-by":"crossref","unstructured":"Altarawneh, H.N., Chemaitelly, H., Ayoub, H.H., Tang, P., Hasan, M.R., Yassine, H.M., Al-Khatib, H.A., Smatti, M.K., Coyle, P., and Al-Kanaani, Z. (2022). Effects of Previous Infection and Vaccination on Symptomatic Omicron Infections. N. Engl. J. Med.","DOI":"10.1056\/NEJMoa2203965"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"2126","DOI":"10.1016\/S0140-6736(21)02758-6","article-title":"Omicron SARS-CoV-2 variant: A new chapter in the COVID-19 pandemic","volume":"398","author":"Karim","year":"2021","journal-title":"Lancet"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1253","DOI":"10.1136\/jim-2021-001853","article-title":"COVID-19 reinfection: A rapid systematic review of case reports and case series","volume":"69","author":"Wang","year":"2021","journal-title":"J. Investig. Med."},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Cocchio, S., Zabeo, F., Facchin, G., Piva, N., Furlan, P., Nicoletti, M., Saia, M., Tonon, M., Mongillo, M., and Russo, F. (2022). The Effectiveness of a Diverse COVID-19 Vaccine Portfolio and Its Impact on the Persistence of Positivity and Length of Hospital Stays: The Veneto Region\u2019s Experience. Vaccines, 10.","DOI":"10.3390\/vaccines10010107"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"315","DOI":"10.1016\/j.cmi.2020.11.028","article-title":"Definitions for coronavirus disease 2019 reinfection, relapse and PCR re-positivity","volume":"27","author":"Yahav","year":"2021","journal-title":"Clin. Microbiol. Infect."},{"key":"ref_26","unstructured":"Experimental Zooprophylactic Institute of Venices (2022, March 16). Diseases and Pathogens: COVID-19. Available online: https:\/\/www.izsvenezie.it\/categoria\/covid-19\/."},{"key":"ref_27","unstructured":"Centers for Disease Control and Prevention (2022, March 04). COVID Data Tracker, Available online: https:\/\/covid.cdc.gov\/covid-data-tracker\/#demographicsovertime."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"30","DOI":"10.1093\/infdis\/jiab556","article-title":"Effectiveness of a Third Dose of BNT162b2 mRNA Vaccine","volume":"225","author":"Saciuk","year":"2022","journal-title":"J. Infect. Dis."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"1288","DOI":"10.1056\/NEJMc2200133","article-title":"Protection against the Omicron Variant from Previous SARS-CoV-2 Infection","volume":"386","author":"Altarawneh","year":"2022","journal-title":"N. Engl. J. Med."},{"key":"ref_30","doi-asserted-by":"crossref","unstructured":"Mallapaty, S. (2022). COVID reinfections surge during Omicron onslaught. Nature, 10.","DOI":"10.1038\/d41586-022-00438-3"},{"key":"ref_31","unstructured":"Veneto Region (2022, March 20). Decision of the Regional Council (DGR) n. 1511, 11\/11\/2021. Available online: https:\/\/www.aulss3.veneto.it\/index.cfm?action=mys.apridoc&iddoc=30075."},{"key":"ref_32","unstructured":"Veneto Region Council (2022, March 20). Temporary Indications for the Priority Use of SARS-CoV-2 Molecular Tests, 29\/12\/2021. Available online: https:\/\/citynews-veronasera.stgy.ovh\/~media\/7262534639411\/nota-tamponi-1-2.pdf."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"1642","DOI":"10.15585\/mmwr.mm695152a3","article-title":"Performance of an Antigen-Based Test for Asymptomatic and Symptomatic SARS-CoV-2 Testing at Two University Campuses\u2014Wisconsin, September\u2013October 2020","volume":"69","author":"Pray","year":"2021","journal-title":"MMWR Morb. Mortal Wkly. Rep."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"1392","DOI":"10.1126\/science.abj2258","article-title":"Hybrid immunity","volume":"372","author":"Crotty","year":"2021","journal-title":"Science"}],"container-title":["International Journal of Environmental Research and Public Health"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1660-4601\/19\/13\/8179\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T23:42:32Z","timestamp":1760139752000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1660-4601\/19\/13\/8179"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2022,7,4]]},"references-count":34,"journal-issue":{"issue":"13","published-online":{"date-parts":[[2022,7]]}},"alternative-id":["ijerph19138179"],"URL":"https:\/\/doi.org\/10.3390\/ijerph19138179","relation":{},"ISSN":["1660-4601"],"issn-type":[{"value":"1660-4601","type":"electronic"}],"subject":[],"published":{"date-parts":[[2022,7,4]]}}}