{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"institution":[{"name":"medRxiv"}],"indexed":{"date-parts":[[2026,1,16]],"date-time":"2026-01-16T12:21:13Z","timestamp":1768566073758,"version":"3.49.0"},"posted":{"date-parts":[[2023,9,5]]},"group-title":"Public and Global Health","reference-count":14,"publisher":"openRxiv","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"accepted":{"date-parts":[[2023,9,5]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                <jats:p>In Portugal, a bivalent COVID-19 vaccine booster was recommended for those with complete primary COVID-19 vaccination, starting on September 6 2022. This study aims to estimate the mRNA bivalent vaccine effectiveness (VE) against COVID-19 infection, hospitalisation and death in the Portuguese population aged 65 and more years with a follow-up of more than six months.<\/jats:p>\n                <jats:sec>\n                  <jats:title>Methods<\/jats:title>\n                  <jats:p>We used a cohort approach to analyse six electronic health registries using deterministic linkage. The follow-up period comprehend September 2022 to May 2023. The outcomes included SARS-CoV-2 infection, COVID-19-related hospitalisation and death. Individuals were considered vaccinated 14 days following a bivalent mRNA COVID-19 vaccine uptake. For each outcome, COVID-19 bivalent VE was estimated as one minus the confounder adjusted hazard ratio of bivalent vaccine vs no bivalent vaccine, estimated by Cox regression with time-dependent vaccine exposure.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Results<\/jats:title>\n                  <jats:p>In the \u2265 80 year-olds, bivalent VE was 23.2 (95%CI: 20.1 to 26.2), 41.3 (95%CI: 34.5 to 47.5) and 50.3 (44.6 to 55.3), against infection, COVID-19-related hospitalisation and death, respectively. In the 65-79 year-old, bivalent VE against infection was 37.7 (35.5 to 39.8), 58.5 (95%CI: 51.9 to 64.2) against hospitalisation and 65.1 (95%CI: 59 to 70.4) against death. Vaccine effectiveness decay was observed for both age groups and in all outcomes, up to 6 months of vaccine uptake.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Conclusions<\/jats:title>\n                  <jats:p>In a population with a high risk of SARS-CoV-2 complications, we observed moderate bivalent VE estimates against severe COVID-19 and low protection against infection. The lower VE estimates observed in the \u2265 80 year-olds should be interpreted in light of the reference group used for the estimation, i.e., individuals with high vaccine coverage (both primary series and multiple boosters). Significant VE decay was observed up to six months of vaccine uptake, which should be considered when preparing future vaccination campaigns.<\/jats:p>\n                <\/jats:sec>","DOI":"10.1101\/2023.09.05.23295025","type":"posted-content","created":{"date-parts":[[2023,9,5]],"date-time":"2023-09-05T17:45:26Z","timestamp":1693935926000},"source":"Crossref","is-referenced-by-count":2,"title":["Bivalent mRNA vaccine effectiveness against COVID-19 infections, hospitalisations and deaths in Portugal: a cohort study based on electronic health records, September 2022 to May 2023"],"prefix":"10.64898","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-1849-1499","authenticated-orcid":false,"given":"Ausenda","family":"Machado","sequence":"first","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5772-2416","authenticated-orcid":false,"given":"Irina","family":"Kislaya","sequence":"additional","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5033-9115","authenticated-orcid":false,"given":"Patricia","family":"Soares","sequence":"additional","affiliation":[]},{"given":"Sarah","family":"Magalh\u00e3es","sequence":"additional","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2264-4723","authenticated-orcid":false,"given":"Ana Paula","family":"Rodrigues","sequence":"additional","affiliation":[]},{"given":"Rafael","family":"Franco","sequence":"additional","affiliation":[]},{"given":"Pedro Pinto","family":"Leite","sequence":"additional","affiliation":[]},{"given":"Carlos Matias","family":"Dias","sequence":"additional","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6230-7209","authenticated-orcid":false,"given":"Baltazar","family":"Nunes","sequence":"additional","affiliation":[]}],"member":"54368","reference":[{"key":"2023090804450559000_2023.09.05.23295025v1.1","unstructured":"Dire\u00e7\u00e3o Geral da Sa\u00fade. Norma n\u00b0 008\/2022 de 02\/09\/2022 atualizada 06\/09\/2022 -Campanha de Vacina\u00e7\u00e3o Sazonal contra a COVID-19: OutonoInverno 2022-2023. Lisboa, Portugal: Dire\u00e7\u00e3o Geral da Sa\u00fade; 2022. p. 3."},{"key":"2023090804450559000_2023.09.05.23295025v1.2","unstructured":"Dire\u00e7\u00e3o Geral da Sa\u00fade. Norma n\u00b0 009\/2022 de 06\/09\/2022 Vacina Comirnaty Original\/Omicron BA.1\u00ae. Dire\u00e7\u00e3o Geral da Sa\u00fade; 2022. p. 3."},{"key":"2023090804450559000_2023.09.05.23295025v1.3","unstructured":"Dire\u00e7\u00e3o Geral da Sa\u00fade. Norma n\u00b0 010\/2022 de 20\/09\/2022 Vacina\u00e7\u00e3o contra a COVID-19: Vacina Comirnaty Original\/Omicron BA.4-5\u00ae. Lisboa, Portugal: Dire\u00e7\u00e3o Geral da Sa\u00fade; 2022."},{"key":"2023090804450559000_2023.09.05.23295025v1.4","unstructured":"Dire\u00e7\u00e3o Geral da Sa\u00fade. Norma n\u00b0 011\/2022 de 21\/09\/2022 Vacina\u00e7\u00e3o contra a COVID-19: Vacina Spikevax Bivalente Original\/Omicron BA.1\u00ae. Lisboa, Portugal: Dire\u00e7\u00e3o Geral da Sa\u00fade; 2022."},{"key":"2023090804450559000_2023.09.05.23295025v1.5","unstructured":"Dire\u00e7\u00e3o Geral da Sa\u00fade. Norma n\u00b0 002\/2021 de 30\/01\/2021 atualizada 02\/09\/2022. Lisboa, Portugal; 2022."},{"key":"2023090804450559000_2023.09.05.23295025v1.6","unstructured":"European Centre for Disease Prevention and Control. COVID-19 Vaccine Tracker. 2023."},{"key":"2023090804450559000_2023.09.05.23295025v1.7","unstructured":"Instituto Nacional de Sa\u00fade Doutor Ricardo Jorge. Genetic diversity of the novel coronavirus SARS-CoV-2 (COVID-19) in Portugal. 2023."},{"key":"2023090804450559000_2023.09.05.23295025v1.8","doi-asserted-by":"publisher","DOI":"10.1038\/s41467-023-38435-3"},{"key":"2023090804450559000_2023.09.05.23295025v1.9","doi-asserted-by":"crossref","unstructured":"Kislaya I , Machado A , Magalh\u00e3es S , Rodrigues AP , Franco R , Leite PP , et al. COVID-19 mRNA vaccine effectiveness (second and first booster dose) against hospitalisation and death during Omicron BA.5 circulation: cohort study based on electronic health records, Portugal, May to July 2022. Eurosurveillance. 2022;27(37).","DOI":"10.2807\/1560-7917.ES.2022.27.37.2200697"},{"issue":"9","key":"2023090804450559000_2023.09.05.23295025v1.10","doi-asserted-by":"crossref","first-page":"e0274008","DOI":"10.1371\/journal.pone.0274008","article-title":"COVID-19 vaccine effectiveness against symptomatic SARS-CoV-2 infections, COVID-19 related hospitalizations and deaths, among individuals aged \u226565 years in Portugal: A cohort study based on data-linkage of national registries February-September 2021","volume":"17","year":"2022","journal-title":"PLoS One"},{"key":"2023090804450559000_2023.09.05.23295025v1.11","doi-asserted-by":"publisher","DOI":"10.2807\/1560-7917.ES.2021.26.38.2100833"},{"key":"2023090804450559000_2023.09.05.23295025v1.12","doi-asserted-by":"publisher","DOI":"10.1016\/S0140-6736(22)00152-0"},{"issue":"19","key":"2023090804450559000_2023.09.05.23295025v1.13","doi-asserted-by":"crossref","first-page":"1818","DOI":"10.1056\/NEJMc2302462","article-title":"Durability of Bivalent Boosters against Omicron Subvariants","volume":"388","year":"2023","journal-title":"N Engl J Med"},{"issue":"23","key":"2023090804450559000_2023.09.05.23295025v1.14","first-page":"1","article-title":"Duration of protection of ancestral-strain monovalent vaccines and effectiveness of bivalent BA. 1 boosters against COVID-19 hospitalisation in England : a test-negative casecontrol study","volume":"3099","year":"2023","journal-title":"Lancet Infect Dis"}],"container-title":[],"original-title":[],"link":[{"URL":"https:\/\/syndication.highwire.org\/content\/doi\/10.1101\/2023.09.05.23295025","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,1,15]],"date-time":"2026-01-15T19:40:25Z","timestamp":1768506025000},"score":1,"resource":{"primary":{"URL":"http:\/\/medrxiv.org\/lookup\/doi\/10.1101\/2023.09.05.23295025"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2023,9,5]]},"references-count":14,"URL":"https:\/\/doi.org\/10.1101\/2023.09.05.23295025","relation":{},"subject":[],"published":{"date-parts":[[2023,9,5]]},"subtype":"preprint"}}