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Introduction: Severe acute respiratory syndrome virus 2 (SARS-CoV-2) has caused over million deaths worldwide, with more than 61,000 deaths in Chile. The Chilean government has implemented a vaccination program against SARS-CoV-2, with over 17.7 million people receiving a complete vaccination scheme. The final target is 18 million individuals. The most common vaccines used in Chile are CoronaVac (Sinovac) and BNT162b2 (Pfizer-Biotech). Given the global need for vaccine boosters to combat the impact of emerging virus variants, studying the immune response to SARS-CoV-2 is crucial. In this study, we characterize the humoral immune response in inoculated volunteers from Chile who received vaccination schemes consisting of two doses of CoronaVac [CoronaVac (2x)], two doses of CoronaVac plus one dose of BNT162b2 [CoronaVac (2x) + BNT162b2 (1x)], and three doses of BNT162b2 [BNT162b2 (3x)]. Methods: We recruited 469 participants from Clínica Dávila in Santiago and the Health Center Víctor Manuel Fernández in the city of Concepción, Chile. Additionally, we included participants who had recovered from COVID-19 but were not vaccinated (RCN). We analyzed antibodies, including anti-N, anti-S1-RBD, and neutralizing antibodies against SARS-CoV-2. Results: We found that antibodies against the SARS-CoV-2 nucleoprotein were significantly higher in the CoronaVac (2x) and RCN groups compared to the CoronaVac (2x) + BNT162b2 (1x) or BNT162b2 (3x) groups. However, the CoronaVac (2x) + BNT162b2 (1x) and BNT162b2 (3x) groups exhibited a higher concentration of S1-RBD antibodies than the CoronaVac (2x) group and RCN group. There were no significant differences in S1-RBD antibody titers between the CoronaVac (2x) + BNT162b2 (1x) and BNT162b2 (3x) groups. Finally, the group immunized with BNT162b2 (3x) had higher levels of neutralizing antibodies compared to the RCN group, as well as the CoronaVac (2x) and CoronaVac (2x) + BNT162b2 (1x) groups. Discussion: These findings suggest that vaccination induces the secretion of antibodies against SARS-CoV-2, and a booster dose of BNT162b2 is necessary to generate a protective immune response. In the current state of the pandemic, these data support the Ministry of Health of the Government of Chile's decision to promote heterologous vaccination as they indicate that a significant portion of the Chilean population has neutralizing antibodies against SARS-CoV-2.

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The evaluation of serological responses to COVID-19 is crucial for population-level surveillance, developing new vaccines, and evaluating the efficacy of different immunization programs. Research and development of point-of-care test technologies remain essential to improving immunity assessment, especially for SARS-CoV-2 variants that partially evade vaccine-induced immune responses. In this work, an impedimetric biosensor based on the immobilization of the recombinant trimeric wild-type spike protein (S protein) on zinc oxide nanorods (ZnONRs) was employed for serological evaluation. We successfully assessed its applicability using serum samples from spike-based COVID-19 vaccines: ChAdOx1-S (Oxford-AstraZeneca) and BNT162b2 (Pfizer-BioNTech). Overall, the ZnONRs/ spike-modified electrode displayed accurate results for both vaccines, showing excellent potential as a tool for assessing and monitoring seroprevalence in the population. A refined outcome of this technology was achieved when the ZnO immunosensor was functionalized with the S protein from the P.1 linage (Gamma variant). Serological responses against samples from vaccinated individuals were acquired with excellent performance. Following studies based on traditional serological tests, the ZnONRs/spike immunosensor data reveal that ChAdOx1-S vaccinated individuals present significantly less antibody-mediated immunity against the Gamma variant than the BNT162b2 vaccine, highlighting the great potential of this point-of-care technology for evaluating vaccine-induced humoral immunity against different SARS-CoV-2 strains.

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BACKGROUND: The Pfizer-BioNTech® BNT162b2 vaccine, provides 95% effectiveness from the second dose onwards. The reported rate of anaphylaxis to COVID-19 vaccines is 4.7 cases/million doses administered. CASE REPORT: 30-year-old female, health professional, history of allergic rhinitis, asthma, reaction to eye cosmetics and adhesive tape: erythema, edema, and local pruritus. Immediately after application of the first dose of Pfizer-BioNTech vaccine, she presented grade III anaphylaxis. The patient was stratified, phenotyped and skin tests with PEG 3350 were positive. A recommendation was issued not to reapply vaccine containing polyethylene glycol and alternatives were offered. CONCLUSIONS: An adequate risk stratification should be performed before applying mRNA-based COVID-19 vaccines for the first time in at-risk groups. In case of anaphylaxis at the first dose, phenotyping and further study with PEG skin tests should be performed and vaccination alternatives should be offered.

INTRODUCCIÓN: La vacuna Pfizer-BioNTech® BNT162b2 proporciona efectividad del 95% a partir de la segunda dosis. La tasa de anafilaxia reportada de vacunas para COVID-19 es de 4.7 casos por millón de dosis administradas. REPORTE DEL CASO: Paciente femenina de 30 años, profesional de la salud, con antecedentes de rinitis alérgica, asma, reacción a productos cosméticos en los párpados y al pegamento de la cinta adhesiva (eritema, edema y prurito local). Posterior a la aplicación de la primera dosis de la vacuna Pfizer-BioNTechÒ tuvo un evento de anafilaxia grado III. Se estratificó, fenotipificó y efectuaron pruebas cutáneas con PEG-3350, que resultaron positivas. Se sugirió no aplicar la aplicar vacuna de refuerzo que contuviera polietilenglicol y se ofrecieron alternativas de tratamiento. CONCLUSIONES: Es importante efectuar la adecuada estratificación de riesgo antes de aplicar las vacunas para COVID-19 basadas en ARNm por primera vez. En caso de anafilaxia es necesario fenotipificar y ampliar el estudio con pruebas cutáneas con PEG, además de otorgar alternativas de vacunación.

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BACKGROUND: Little is currently known about vaccine effectiveness (VE) for either 2 doses of Oxford-AstraZeneca (ChAdOx1) viral vector vaccine or CoronaVac (Instituto Butantan) inactivated viral vaccine followed by a third dose of mRNA vaccine (Pfizer/BioNTech) among healthcare workers (HCWs). METHODS: We conducted a retrospective cohort study among HCWs (aged ≥18 years) working in a private healthcare system in Brazil from January to December 2021. VE was defined as 1 - incidence rate ratio (IRR), with IRR determined using Poisson models with the occurrence of laboratory-confirmed coronavirus disease 2019 (COVID-19) infection as the outcome, adjusting for age, sex, and job type. We compared those receiving viral vector or inactivated viral primary series (2 doses) with those who received an mRNA booster. RESULTS: A total of 11 427 HCWs met the inclusion criteria. COVID-19 was confirmed in 31.5% of HCWs receiving 2 doses of CoronaVac vaccine versus 0.9% of HCWs receiving 2 doses of CoronaVac vaccine with mRNA booster (P < .001) and 9.8% of HCWs receiving 2 doses of ChAdOx1 vaccine versus 1% among HCWs receiving 2 doses of ChAdOx1 vaccine with mRNA booster (P < .001). In the adjusted analyses, the estimated VE was 92.0% for 2 CoronaVac vaccines plus mRNA booster and 60.2% for 2 ChAdOx1 vaccines plus mRNA booster, when compared with those with no mRNA booster. Of 246 samples screened for mutations, 191 (77.6%) were Delta variants. CONCLUSIONS: While 2 doses of ChAdOx1 or CoronaVac vaccines prevent COVID-19, the addition of a Pfizer/BioNTech booster provided significantly more protection.

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BACKGROUND: The present case aims to describe a previously healthy man who presented multiple attacks of transient monocular visual loss after Pfizer-BioNTech COVID-19 vaccination and to discuss the possible mechanisms related to occurrence of this condition. CASE PRESENTATION: We report a case of multiple attacks of transient monocular visual loss in a previously healthy middle-aged man two weeks after Pfizer-BioNTech COVID-19 vaccination. TVL attacks were described as sudden and painless complete visual loss, lasting about one minute, followed by a full recovery. He presented several non-simultaneous attacks in both eyes, 16 in the right eye, and 2 in the left eye on the same day, fifteen days after receiving the second dose of the Pfizer-BioNTech COVID-19 vaccine. The brain's magnetic resonance angiography, echocardiogram, and doppler ultrasound imaging of the carotid and vertebral arteries were non-revealing. The complete blood exam revealed a slightly elevated C-reactive protein test. We assessed fundus examination during the transient visual loss attack and revealed diffuse vascular narrowing for both arterial and venous branches, notably in the emergence of the optic disc in right eye. In addition, the circumpapillary optical coherence tomography angiography (OCTA) vessel density map was reduced. Oral verapamil hydrochloride 60 mg twice daily was initiated, and the attacks of transient visual loss improved after two days. CONCLUSIONS: To date, and the best of our knowledge, this is the first case report of multiple transient monocular visual loss attacks due to retinal vasospasm in a previously healthy middle-aged man documented by fundus retinography and OCTA. We discuss in this article the possible association of retinal vasospasm and Pfizer-BioNTech COVID-19 vaccination, probably related to vaccine-induced inflammation.

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The differential diagnosis of the metastatic axillary lymphadenopathies of breast cancer with which they occur secondary to the Pfizer-BioNTech vaccine against COVID-19, is imperative. In a series of cases, we analyzed the characteristics of unilateral axillary lymphadenopathy in patients after Pfizer-BioNTech vaccination. Axillary lymphadenopathy were observed ipsilateral to the vaccination arm. The axillary ultrasound defined these as reactive and that they disappeared in 3 weeks. The pathological findings were benign. The anamnesis, the place and date of vaccination and the radiological findings, play an essential role to carry out a correct differential diagnosis and follow-up of these adenopathies.

El diagnóstico diferencial de las adenopatías axilares metastásicas del cáncer de mama con las que se producen secundarias a la vacuna de Pfizer-BioNTech contra la COVID-19 es imperioso. Analizamos una serie de casos con las características de las adenopatías axilares unilaterales tras la administración de la vacuna de Pfizer-BioNTech. Se observaron adenopatías axilares homolaterales al brazo de vacunación. La ecografía axilar las definió como reactivas y que desaparecían en 3 semanas. Los hallazgos anatomopatológicos fueron de benignidad. La anamnesis, el lugar y la fecha de vacunación, así como los hallazgos radiológicos, desempeñan un papel esencial para realizar un correcto diagnóstico deferencial y el seguimiento de estas adenopatías.

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The SARS-CoV-2 virus was detected for the first time in December 2019 in Wuhan, China. Currently, this virus has spread around the world, and new variants have emerged. This new pandemic virus provoked the rapid development of diagnostic tools, therapies and vaccines to control this new disease called COVID-19. Antibody detection by ELISA has been broadly used to recognize the number of persons infected with this virus or to evaluate the response of vaccinated individuals. As the pandemic spread, new questions arose, such as the prevalence of antibodies after natural infection and the response induced by the different vaccines. In Mexico, as in other countries, mRNA and viral-vectored vaccines have been widely used among the population. In this work, we developed an indirect ELISA test to evaluate S1 antibodies in convalescent and vaccinated individuals. By using this test, we showed that IgG antibodies against the S1 protein of SARS-CoV-2 were detected up to 42 weeks after the onset of the symptoms, in contrast to IgA and IgM, which decreased 14 weeks after the onset of symptoms. The evaluation of the antibody response in individuals vaccinated with Pfizer-BioNTech and CanSinoBio vaccines showed no differences 2 weeks after vaccination. However, after completing the two doses of Pfizer-BioNTech and the one dose of CanSinoBio, a significantly higher response of IgG antibodies was observed in persons vaccinated with Pfizer-BioNTech than in those vaccinated with CanSinoBio. In conclusion, these results confirm that after natural infection with SARS-CoV-2, it is possible to detect antibodies for up to 10 months. Additionally, our results showed that one dose of the CanSinoBio vaccine induces a lower response of IgG antibodies than that induced by the complete scheme of the Pfizer-BioNTech vaccine.

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