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Falência vacinal secundária contra o sarampo: casos identificados em 2024
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Advisor(s)
Abstract(s)
Portugal alcançou o estatuto de eliminação do sarampo em 2015, no entanto, continuam a ocorrer surtos esporádicos, incluindo casos em indivíduos previamente vacinados. O teste de avidez das IgG avalia a força de ligação das imunoglobulinas ao seu antigénio específico, a qual aumenta ao longo da resposta imunitária, permitindo assim distinguir infeções primárias de respostas imunes pré-existentes.
Este estudo teve como objetivo identificar casos de falência vacinal secundária contra o sarampo que ocorreram em 2024 utilizando o teste de avidez das IgG. Em 2024 foram confirmados 35 casos de sarampo em pacientes com idades entre 1 e 61 anos. A avidez de IgG foi avaliada em 17 casos (48,6%): 14 vacinados com duas doses de VASPR e 3 com estado vacinal desconhecido.
Todos os soros, exceto um, foram colhidos durante a primeira semana após o início do exantema e utilizados reagentes comerciais com ureia como agente desnaturante.
O RNA do vírus do sarampo foi detetado em todos os 16 casos. A IgM foi positiva em 6 pacientes: 5 vacinados e 1 com vacinação desconhecida. IgG de baixa avidez (IA < 40%) ocorreu apenas no paciente com vacinação desconhecida e IgM positiva, indicando infeção primária. Os outros 2 pacientes com vacinação não documentada apresentaram IgG de alta avidez e IgM negativa sugerindo falência vacinal secundária ou reinfeção. Todos os 14 casos vacinados apresentaram IgG de alta avidez (IA > 60%), sendo 5 também positivos para a IgM.
O estudo identificou uma infeção primária e dois casos de falência vacinal secundária ou reinfeção em indivíduos com status desconhecido. Todos os casos em vacinados ocorreram em adultos, mais de 10 anos após a segunda dose da VASPR, sendo compatíveis com uma falência vacinal secundária e representando 40% dos casos de 2024. Isso reflete o contexto pós-eliminação em Portugal,
onde a baixa exposição ao vírus selvagem reduz o reforço natural da imunidade, permitindo sintomas moderados e replicação viral apesar da vacinação prévia.
Portugal achieved measles elimination status in 2015; however, sporadic outbreaks continue to occur, including in vaccinated individuals. The IgG avidity test assesses the net force by which antibodies bind specific antigen, which increases over the course of the immune response, allowing differentiation between primary infections and pre-existing immune responses. This study aimed to identify cases of secondary measles vaccine failure that occurred in 2024 using the IgG avidity test. In 2024, 35 measles cases were confirmed in patients aged 1–61 years. IgG avidity was assessed in 17 cases (48.6%): 14 fully vaccinated with two MMR doses and 3 with unknown vaccination status. All sera, except one, were collected during the first week after the onset of the rash and analysed using commercial reagents with urea as a denaturing agent. Measles RNA was detected in al l 16 cases. IgM was positive in 5 patients: 5 vaccinated and 1 with unknown status. Low-avidi ty IgG (AI < 40%) was observed only in the patient with unknown vaccination and positive IgM, indicating a primary infection. The other 2 patients wi th undocumented status showed high-avidi ty IgG and negative IgM, suggesting secondary failure or reinfection. Al l 14 vaccinated cases had high-avidi ty IgG (AI >60%), with 5 also positive for IgM. The study identified one primary infection and two cases of secondary vaccine failure or reinfection among individuals with unknown status. All vaccinated cases occurred in adults, more than 10 years af ter MMR second dose which is consistent with a secondary vaccine failure, representing 40% of 2024 cases, reflecting Portugal’s post-elimination context, where limited exposure to wild virus reduces natural immune boosting, allowing moderate symptoms and viral replication despite prior vaccination.
Portugal achieved measles elimination status in 2015; however, sporadic outbreaks continue to occur, including in vaccinated individuals. The IgG avidity test assesses the net force by which antibodies bind specific antigen, which increases over the course of the immune response, allowing differentiation between primary infections and pre-existing immune responses. This study aimed to identify cases of secondary measles vaccine failure that occurred in 2024 using the IgG avidity test. In 2024, 35 measles cases were confirmed in patients aged 1–61 years. IgG avidity was assessed in 17 cases (48.6%): 14 fully vaccinated with two MMR doses and 3 with unknown vaccination status. All sera, except one, were collected during the first week after the onset of the rash and analysed using commercial reagents with urea as a denaturing agent. Measles RNA was detected in al l 16 cases. IgM was positive in 5 patients: 5 vaccinated and 1 with unknown status. Low-avidi ty IgG (AI < 40%) was observed only in the patient with unknown vaccination and positive IgM, indicating a primary infection. The other 2 patients wi th undocumented status showed high-avidi ty IgG and negative IgM, suggesting secondary failure or reinfection. Al l 14 vaccinated cases had high-avidi ty IgG (AI >60%), with 5 also positive for IgM. The study identified one primary infection and two cases of secondary vaccine failure or reinfection among individuals with unknown status. All vaccinated cases occurred in adults, more than 10 years af ter MMR second dose which is consistent with a secondary vaccine failure, representing 40% of 2024 cases, reflecting Portugal’s post-elimination context, where limited exposure to wild virus reduces natural immune boosting, allowing moderate symptoms and viral replication despite prior vaccination.
Description
Keywords
Sarampo Doenças Evitáveis por Vacinação Vigilância Laboratorial Efetividade das Vacinas Doenças Infecciosas Portugal
Pedagogical Context
Citation
Boletim Epidemiológico Observações. 2025 maio-agosto;14(38): 28-31
Publisher
Instituto Nacional de Saúde Doutor Ricardo Jorge, IP