Kislaya, IrinaCasaca, PedroBorges, VítorSousa, CarlosFerreira, Bibiana I.Fonte, AnaFernandes, EugéniaDias, Carlos MatiasDuarte, SílviaAlmeida, José PedroGrenho, InêsCoelho, LuísFerreira, RitaFerreira, Patrícia PitaBorges, Cláudia MedeirosIsidro, JoanaPinto, MiguelMenezes, LuísSobral, DanielNunes, AlexandraSantos, DanielaGonçalves, António MaiaVieira, LuísGomes, João PauloLeite, Pedro PintoNunes, BaltazarMachado, AusendaPeralta-Santos, André2024-01-222024-01-222023-03Emerg Infect Dis. 2023 Mar;29(3):569-575. doi: 10.3201/eid2903.221367. Epub 2023 Feb 31080-6040http://hdl.handle.net/10400.18/8950Author affiliations: Instituto Nacional de Saúde Doutor Ricardo Jorge, Lisbon, Portugal (I. Kislaya, V. Borges, C. Matias Dias, S. Duarte, L. Coelho, R. Ferreira, J. Isidro, M. Pinto, D. Sobral, A. Nunes, D. Santos, L. Vieira, J.P. Gomes, B. Nunes, A. Machado).We estimated comparative primary and booster vaccine effectiveness (VE) of SARS-CoV-2 Omicron BA.5 and BA.2 lineages against infection and disease progression. During April-June 2022, we implemented a case-case and cohort study and classified lineages using whole-genome sequencing or spike gene target failure. For the case-case study, we estimated the adjusted odds ratios (aORs) of vaccination using a logistic regression. For the cohort study, we estimated VE against disease progression using a penalized logistic regression. We observed no reduced VE for primary (aOR 1.07 [95% CI 0.93-1.23]) or booster (aOR 0.96 [95% CI 0.84-1.09]) vaccination against BA.5 infection. Among BA.5 case-patients, booster VE against progression to hospitalization was lower than that among BA.2 case-patients (VE 77% [95% CI 49%-90%] vs. VE 93% [95% CI 86%-97%]). Although booster vaccination is less effective against BA.5 than against BA.2, it offers substantial protection against progression from BA.5 infection to severe disease.engBA.2BA.5COVID-19OmicronSARS-CoV-2Coronavirus DiseaseDeathHospitalizationPostinfection Vaccine EffectivenessRespiratory InfectionsSevere Acute Respiratory Syndrome Coronavirus 2Vaccine-preventable DiseasesVirusesPortugalInfecções RespiratóriasDoenças Evitáveis pela VacinaçãoDeterminantes da Saúde e da Doençajournal article10.3201/eid2903.221367