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Background: The lack of precise definitions and terminological consensus about the impact studies of COVID-19 vaccination leads to confusing statements from the scientific community about what a vaccination impact study is. Objective: The present work presents a narrative review, describing and discussing COVID-19 vaccination impact studies, mapping their relevant characteristics, such as study design, approaches and outcome variables, while analyzing their similarities, distinctions, and main insights. Methods: The articles screening, regarding title, abstract, and full-text reading, included papers addressing perspectives about the impact of vaccines on population outcomes. The screening process included articles published before June 10, 2022, based on the initial papers' relevance to this study's research topics. The main inclusion criteria were data analyses and study designs based on statistical modelling or comparison of pre- and post-vaccination population. Results: The review included 18 studies evaluating the vaccine impact in a total of 48 countries, including 32 high-income countries (United States, Israel, and 30 Western European countries) and 16 low- and middle-income countries (Brazil, Colombia, and 14 Eastern European countries). We summarize the main characteristics of the vaccination impact studies analyzed in this narrative review. Conclusion: Although all studies claim to address the impact of a vaccination program, they differ significantly in their objectives since they adopt different definitions of impact, methodologies, and outcome variables. These and other differences are related to distinct data sources, designs, analysis methods, models, and approaches.

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Resumo O presente texto trata de refletir sobre a campanha de vacinação contra COVID-19 no Brasil à luz da consideração das evidências científicas no processo de tomada de decisão. O Brasil possui um dos maiores e mais completos programas de vacinação do mundo, o Programa Nacional de Imunizações (PNI). Infelizmente, no contexto atual, com as interferências políticas do governo federal, o PNI perdeu seu protagonismo na condução da campanha de vacinação contra a COVID-19. Apesar de ser uma campanha de vacinação com muito potencial e uma das mais aceitas pela população entre os países no mundo, apresentou muitos problemas e deixou diversas lacunas no cenário brasileiro. Nesse sentido, é fundamental que as evidências científicas de qualidade produzidas nesse período possam guiar uma remodelagem constante da estratégia de vacinação. Quatro pontos merecem ser destacados: 1) o intervalo entre as doses; 2) a intercambialidade entre vacinas; 3) a vacinação em adolescentes; e 4) a necessidade de melhores evidências para definir a estratégia de vacinação em certos grupos e faixas etárias.

Abstract This paper reflects on the vaccination campaign against COVID-19 in Brazil in light of the consideration of scientific evidence in the decision-making process. Brazil has one of the largest and most complete vaccination programs in the world, the National Immunization Program (Programa Nacional de Imunizações or PNI). Unfortunately, in the current context, with the political interference of the federal government, the PNI lost its role in conducting the vaccination campaign against COVID-19. Despite being a vaccination campaign with a lot of potential and one of the most accepted by the population among countries in the world, it presented many problems and left several gaps in the Brazilian scenario. In this sense, it is essential that the quality scientific evidence produced during this period can guide a constant remodeling of the vaccination strategy. Four points deserve to be highlighted: 1) the interval between doses; 2) the interchangeability between vaccines; 3) vaccination in children and adolescentes; and 4) the need for better evidence to define the vaccination strategy in certain groups and age groups.

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BACKGROUND: The COVID-19 pandemic has disrupted the delivery of immunisation services globally. Many countries have postponed vaccination campaigns out of concern about infection risks to the staff delivering vaccination, the children being vaccinated, and their families. The World Health Organization recommends considering both the benefit of preventive campaigns and the risk of SARS-CoV-2 transmission when making decisions about campaigns during COVID-19 outbreaks, but there has been little quantification of the risks. METHODS: We modelled excess SARS-CoV-2 infection risk to vaccinators, vaccinees, and their caregivers resulting from vaccination campaigns delivered during a COVID-19 epidemic. Our model used population age structure and contact patterns from three exemplar countries (Burkina Faso, Ethiopia, and Brazil). It combined an existing compartmental transmission model of an underlying COVID-19 epidemic with a Reed-Frost model of SARS-CoV-2 infection risk to vaccinators and vaccinees. We explored how excess risk depends on key parameters governing SARS-CoV-2 transmissibility, and aspects of campaign delivery such as campaign duration, number of vaccinations, and effectiveness of personal protective equipment (PPE) and symptomatic screening. RESULTS: Infection risks differ considerably depending on the circumstances in which vaccination campaigns are conducted. A campaign conducted at the peak of a SARS-CoV-2 epidemic with high prevalence and without special infection mitigation measures could increase absolute infection risk by 32 to 45% for vaccinators and 0.3 to 0.5% for vaccinees and caregivers. However, these risks could be reduced to 3.6 to 5.3% and 0.1 to 0.2% respectively by use of PPE that reduces transmission by 90% (as might be achieved with N95 respirators or high-quality surgical masks) and symptomatic screening. CONCLUSIONS: SARS-CoV-2 infection risks to vaccinators, vaccinees, and caregivers during vaccination campaigns can be greatly reduced by adequate PPE, symptomatic screening, and appropriate campaign timing. Our results support the use of adequate risk mitigation measures for vaccination campaigns held during SARS-CoV-2 epidemics, rather than cancelling them entirely.

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Resumen Desde 1982, cada año el Departamento de Inmunizaciones del Ministerio de Salud de Chile lleva a cabo la campaña de vacunación contra influenza junto con las Secretarías Regionales Ministeriales-SEREMI, Servicios de Salud y centros de atención primaria de salud. Con los objetivos de prevenir mortalidad y morbilidad grave en grupos de mayor riesgo y de preservar la integridad de los servicios de salud, hasta el 2020 las campañas de vacunación contra influenza serían las más grandes implementadas en Chile, para dar paso, el 2021, a la vacunación contra SARS-CoV-2. Obedeciendo a cambios demográficos y epidemiológicos locales y acogiendo los avances científicos sobre seguridad e inmunogenicidad de la vacuna, el incremento de las vacunas influenza disponibles en Chile forma parte de la planificación anual de la campaña. El 2020, sin embargo, la Campaña Influenza tuvo que ser re-planificada en curso como consecuencia de la incorporación de nuevos grupos a vacunar según dispuso la modificación de la alerta sanitaria por brote de SARS-CoV-2 del 6 de marzo de 2020. Así, de 6.799.800 de dosis, el Departamento de Inmunizaciones logró en menos de dos meses aumentar la disponibilidad a 8.480.325, y cumplir con el compromiso de garantizar el acceso de los grupos de riesgo al beneficio de la vacunación estatal gratuita.

Abstract In Chile, the Immunization Department of the Ministry of Health has carried out the seasonal influenza vaccination campaign annually since 1982 in collaboration with the national health services, regional health offices, and primary health care centres. With the aim of preventing deaths and serious morbidity in high-risk groups and preserving the integrity of health services, the seasonal influenza campaign had been the largest implemented in Chile until 2020, since in 2021 the vaccination campaign against SARS-CoV-2 is expected to become the largest ever implemented. In response to local demographic and epidemiological changes, and taking into account the new scientific evidence on the safety and immunogenicity of vaccines, the influenza vaccines available in Chile would increase annually as a result of campaign planning. In 2020, the influenza campaign had to be re-planned while in progress due to the addition of new high-risk groups to be vaccinated in accordance with the SARS-CoV-2 pandemic health alert modification of March 6th, 2020. Over the course of three weeks, the Immunization Department managed to increase the doses of available influenza vaccines from 6,799,800 previously agreed upon to 8,480,325 and thus serve high-risk groups, guaranteeing their access to state funded influenza vaccination.

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Haiti has historically vaccinated between 100,000 and 300,000 dogs annually against rabies, however national authorities have not been able to reach and maintain the 70% coverage required to eliminate the canine rabies virus variant. Haiti conducts massive dog vaccination campaigns on an annual basis and utilizes both central point and door-to-door methods. These methods require that dog owners are aware of the dates and locations of the campaign. To improve this awareness among dog owners, 600,000 text messages were sent to phones in two Haitian communes (Gonaives and Saint-Marc) to remind dog owners to attend the campaign. Text messages were delivered on the second day and at the mid-point of the campaign. A post-campaign household survey was conducted to assess dog owner's perception of the text messages and the impact on their participation in the vaccination campaign. Overall, 147 of 160 (91.9%) text-receiving dog owners indicated the text was helpful, and 162 of 187 (86.6%) responding dog owners said they would like to receive text reminders during future rabies vaccination campaigns. In areas hosting one-day central point campaigns, dog owners who received the text were 2.0 (95% CI 1.1, 3.6) times more likely to have participated in the campaign (73.1% attendance among those who received the text vs 36.4% among those who did not). In areas incorporating door-to-door vaccination over multiple days there was no significant difference in participation between dog owners who did and did not receive a text. Text message reminders were well-received and significantly improved campaign attendance, indicating that short message service (SMS) alerts may be a successful strategy in low resource areas with large free roaming dog populations.

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BACKGROUND: In Argentina, vaccination with Brucella abortus Strain 19 vaccine is mandatory. The objective of the study was to develop and test a method for evaluating, in an innovative way, some farmers' and veterinarians' management practices in relation to brucellosis and to assess the vaccination campaign and coverage. The work took place in Brandsen and Navarro districts. Four questionnaires were designed (for officials from Local Sanitary Entities, vaccinators, vet practitioners and farmers). Responses were coded as "ideal" (0) and "not ideal" (1). To assess the relative weight of each question ("item"), experts ranked the items according to their impact on management practices and vaccination. A weighted score was then calculated. A higher weighted score was assigned to the worse practices. Farmers obtaining a global weighted score above the third quartile were classified as "inappropriately managed farms", to be compared per type of production system and district. To assess the immunization coverage, female calves were sampled 30 to 50 days post vaccination; they were expected to react positively to serological diagnostic tests (DT+). RESULTS: There were significantly more inappropriately managed farms and higher global scores among beef farmers and in Brandsen. Eighty three percent (83%) of female calves were DT+, significantly under the ideal immunization coverage (95%). Only 48% of farms were considered well vaccinated. DT+ results were positively associated with the Brandsen district (OR = 25.94 [4.60-1146.21] and with the farms having more than 200 cow heads ((OR = 78.34 [4.09-1500.00]). On the contrary, DT+ were less associated with vaccinators being veterinary practitioners (OR = 0.07 [0.006-0.78]). Farmers are well advised by their veterinary practitioners but they should improve some management practices. CONCLUSIONS: The vaccination campaign is globally well implemented, but the immunization coverage and some vaccinators' practices should be improved. This study leads to a better understanding of the most common used management and control practices regarding brucellosis, which affect its epidemiology. Any vaccination campaign should be periodically assessed to highlight possible fails. The described methodology can be extrapolated to other countries and different contexts.

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Rabies, a zoonosis found throughout the globe, is caused by a virus of the Lyssavirus genus. The disease is transmitted to humans through the inoculation of the virus present in the saliva of infected mammals. Since its prognosis is usually fatal for humans, nationwide public campaigns to vaccinate dogs and cats against rabies aim to break the epidemiological link between the virus and its reservoirs in Brazil. During 12 months we evaluated the active immunity of dogs first vaccinated (booster shot at 30 days after first vaccination) against rabies using the Fuenzalida-Palácios modified vaccine in the urban area of Botucatu city, São Pauto state, Brazil. Of the analyzed dogs, 54.7% maintained protective titers (≥0.5 IU/mL) for 360 days after the first vaccination whereas 51.5% during all the study period. The present results suggest a new vaccination schedule for dogs that have never been vaccinated. In addition to the first dose of vaccine, two others are recommended: the second at 30 days after the first and the third dose at 180 days after the first for the maintenance of protective titers during 12 months.

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Background Rabies, a zoonosis found throughout the globe, is caused by a virus of theLyssavirus genus. The disease is transmitted to humans through the inoculation of the virus present in the saliva of infected mammals. Since its prognosis is usually fatal for humans, nationwide public campaigns to vaccinate dogs and cats against rabies aim to break the epidemiological link between the virus and its reservoirs in Brazil.Findings During 12 months we evaluated the active immunity of dogs first vaccinated (booster shot at 30 days after first vaccination) against rabies using the Fuenzalida-Palácios modified vaccine in the urban area of Botucatu city, São Pauto state, Brazil. Of the analyzed dogs, 54.7% maintained protective titers (≥0.5 IU/mL) for 360 days after the first vaccination whereas 51.5% during all the study period.Conclusions The present results suggest a new vaccination schedule for dogs that have never been vaccinated. In addition to the first dose of vaccine, two others are recommended: the second at 30 days after the first and the third dose at 180 days after the first for the maintenance of protective titers during 12 months.(AU)

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BACKGROUND: Rabies, a zoonosis found throughout the globe, is caused by a virus of the Lyssavirus genus. The disease is transmitted to humans through the inoculation of the virus present in the saliva of infected mammals. Since its prognosis is usually fatal for humans, nationwide public campaigns to vaccinate dogs and cats against rabies aim to break the epidemiological link between the virus and its reservoirs in Brazil. FINDINGS: During 12 months we evaluated the active immunity of dogs first vaccinated (booster shot at 30 days after first vaccination) against rabies using the Fuenzalida-Palácios modified vaccine in the urban area of Botucatu city, São Pauto state, Brazil. Of the analyzed dogs, 54.7% maintained protective titers (≥0.5 IU/mL) for 360 days after the first vaccination whereas 51.5% during all the study period. CONCLUSIONS: The present results suggest a new vaccination schedule for dogs that have never been vaccinated. In addition to the first dose of vaccine, two others are recommended: the second at 30 days after the first and the third dose at 180 days after the first for the maintenance of protective titers during 12 months.

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Rabies, a zoonosis found throughout the globe, is caused by a virus of the Lyssavirus genus. The disease is transmitted to humans through the inoculation of the virus present in the saliva of infected mammals. Since its prognosis is usually fatal for humans, nationwide public campaigns to vaccinate dogs and cats against rabies aim to break the epidemiological link between the virus and its reservoirs in Brazil. During 12 months we evaluated the active immunity of dogs first vaccinated (booster shot at 30 days after first vaccination) against rabies using the Fuenzalida-Palácios modified vaccine in the urban area of Botucatu city, São Pauto state, Brazil. Of the analyzed dogs, 54.7% maintained protective titers (≥0.5 IU/mL) for 360 days after the first vaccination whereas 51.5% during all the study period. The present results suggest a new vaccination schedule for dogs that have never been vaccinated. In addition to the first dose of vaccine, two others are recommended: the second at 30 days after the first and the third dose at 180 days after the first for the maintenance of protective titers during 12 months.(AU)

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