Publications by authors named "Tirza de Leon"

Article Synopsis
  • - Norovirus is a leading cause of acute gastroenteritis (AGE), and the study aimed to gather data on its prevalence and impact in Panama while following COVID-19 safety protocols.
  • - The research involved monitoring children under two years old through community and hospital-based surveillance, with 400 participants contributing data over several months from January to September 2020, despite interruptions due to the pandemic.
  • - The results indicated a total of 185 AGE cases in the longitudinal study, with a specific incidence of norovirus-related cases being relatively low (0.3 episodes per 100 child-months), highlighting the need for ongoing research and effective preventive measures.
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Article Synopsis
  • Incidence rates of respiratory syncytial virus-associated lower respiratory tract illness (RSV-LRTI) in infants were assessed in low- and middle-income countries (LMICs) as existing data was limited.
  • The study followed 2,094 infants from 10 LMICs over one year, using surveillance and testing to identify cases during the COVID-19 pandemic.
  • Results indicated a low incidence of RSV-LRTI (1.5% of infants) and all-cause lower respiratory tract infections, likely influenced by reduced viral activity during the pandemic.
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  • A study was conducted to evaluate the safety and immune response of a new RSV vaccine (ChAd155-RSV) in infants aged 6-7 months, comparing different doses and an active comparator.* -
  • The trial involved 201 infants, with results indicating that the vaccine had a safety profile comparable to existing childhood vaccines, and did not lead to adverse respiratory effects associated with RSV infections.* -
  • Higher doses of the ChAd155-RSV vaccine produced stronger immune responses, with increased antibody levels observed after vaccination, especially following the second dose.*
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  • Sabin strains in oral poliovirus vaccines (OPV) can revert to harmful forms, prompting the development of a new OPV2 (nOPV2) designed to remain stable and reduce disease-causing strains in populations with low vaccination rates.
  • In clinical trials conducted in Panama, infants received either monovalent OPV2 (mOPV2) or nOPV2, and researchers analyzed the poliovirus shed in their stools for genetic and phenotypic changes post-vaccination.
  • Results indicated that the Sabin-2 strain rapidly reverts to virulent forms, but nOPV2 showed little to no increase in neurovirulence, indicating it may be a safer option with significantly lower paralysis rates
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Novel oral poliovirus vaccine type 2 (nOPV2) is being developed to reduce the rare occurrence of disease and outbreaks associated with the genetic instability of the Sabin vaccine strains. Children aged 1 to 5 years were enrolled in two related clinical studies to assess safety, immunogenicity, shedding rates and properties of the shed virus following vaccination with nOPV2 (two candidates) versus traditional Sabin OPV type 2 (mOPV2). The anticipated pattern of reversion and increased virulence was observed for shed Sabin-2 virus, as assessed using a mouse model of poliovirus neurovirulence.

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Background: Primary intestinal immunity through viral replication of live oral vaccine is key to interrupt poliovirus transmission. We assessed viral fecal shedding from infants administered Sabin monovalent poliovirus type 2 vaccine (mOPV2) or low and high doses of 2 novel OPV2 (nOPV2) vaccine candidates.

Methods: In 2 randomized clinical trials in Panama, a control mOPV2 study (October 2015 to April 2016) and nOPV2 study (September 2018 to October 2019), 18-week-old infants vaccinated with bivalent oral poliovirus vaccine/inactivated poliovirus vaccine received 1 or 2 study vaccinations 28 days apart.

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Background: Continued emergence and spread of circulating vaccine-derived type 2 polioviruses and vaccine-associated paralytic poliomyelitis from Sabin oral poliovirus vaccines (OPVs) has stimulated development of two novel type 2 OPV candidates (OPV2-c1 and OPV2-c2) designed to have similar immunogenicity, improved genetic stability, and less potential to reacquire neurovirulence. We aimed to assess safety and immunogenicity of the two novel OPV candidates compared with a monovalent Sabin OPV in children and infants.

Methods: We did two single-centre, multi-site, partly-masked, randomised trials in healthy cohorts of children (aged 1-4 years) and infants (aged 18-22 weeks) in Panama: a control phase 4 study with monovalent Sabin OPV2 before global cessation of monovalent OPV2 use, and a phase 2 study with low and high doses of two novel OPV2 candidates.

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We assessed EV-D68 epidemiology and phylogenetics among children aged ≤9 years hospitalized with severe acute respiratory illnesses at five sites in Panama and El Salvador during 2012-2013. Respiratory specimens positive for enterovirus or rhinovirus were tested by real-time RT-PCR for EV-D68, and partial VP1 gene sequences were determined. Of 715 enrolled children, 17 from sites in both countries were EV-D68-positive and commonly had a history of asthma or wheezing.

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Article Synopsis
  • Hepatitis A virus (HAV) remains a significant health issue in Latin America, with a shift from high to intermediate levels of endemicity prompting interest in national immunization programs (NIPs) for children, particularly regarding the long-term effectiveness of 1-dose versus 2-dose vaccination schedules.
  • In a study involving 1,199 children across two surveys conducted 8 and 10 years post-vaccination with the Havrix vaccine, the results showed that seropositivity rates and antibody concentrations were significantly lower in the 1-dose group compared to the 2-dose group.
  • The findings indicate that long-term antibody persistence from a single dose is not non-inferior to
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Background And Objectives: Although acute respiratory illness (ARI) is a leading cause of hospitalization among young children, few data are available about cost of hospitalization in middle-income countries. We estimated direct and indirect costs associated with severe ARI resulting in hospitalization among children aged <10 years in El Salvador and Panama through the societal perspective.

Methods: During 2012 and 2013, we surveyed caregivers of children hospitalized with ARI about their direct medical (i.

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Background: Oseltamivir reduces symptom duration among children with uncomplicated influenza, but few data exist on treatment efficacy and tolerability among hospitalized children, particularly among infants aged <1 year. We evaluated tolerability and efficacy of oseltamivir treatment of children aged 0-9 years hospitalized with influenza.

Methods: We conducted a double-blind, randomized, placebo-controlled trial at tertiary care hospitals in El Salvador and Panama.

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We evaluated the added value of collecting both nasal and oropharyngeal swabs, compared with collection of nasal swabs alone, for detection of common respiratory viruses by reverse transcription-polymerase chain reaction in hospitalized children aged <10 years. Nasal swabs had equal or greater sensitivity than oropharyngeal swabs for detection of respiratory syncytial virus, adenovirus, human metapneumovirus, rhinovirus, and influenza virus but not parainfluenza virus. The addition of an oropharyngeal swab, compared with use of a nasal swab alone, increased the frequency of detection of each respiratory virus by no more than 10% in children aged <10 years.

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Background: The efficacy of a rotavirus vaccine against severe rotavirus gastroenteritis when coadministered with routine Expanded Program on Immunization (EPI) vaccines including oral polio vaccine (OPV) was evaluated in this study.

Methods: Double-blind, randomized (2:1), placebo-controlled study conducted across 6 Latin American countries. Healthy infants (N = 6568) 6 to 12 weeks of age received 2 doses of RIX4414 vaccine or placebo following a 0, 1- to 2-month schedule.

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This multicentre study was designed to establish the reactogenicity and immunogenicity profiles of primary and booster vaccination with diphtheria, tetanus, and pertussis whole-cell-hepatitis B/Haemophilus influenzae type-b (DTPw-HB/Hib) administered as either a syringe mix or as separate injections in 400 Latin American children. Both vaccine regimens were equally well tolerated and elicited post-primary excellent seropositivity rates at or close to 100% for all five component antigens. With regard to HB, 100% of subjects in the combined vaccination group, and 98.

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