1179. PCV13 Pediatric Routine Schedule Completion and Adherence Before and During the COVID-19 Pandemic in the US

Background Coronavirus Disease 2019 (COVID) mitigation measures may have unintended consequences, such as reduced or delayed access to routine immunizations. This study examined (1) PCV13 routine vaccination completion and adherence (C&A) among US infants before and during the COVID pandemic and (2) the relationship between primary dose C&A and booster dose C&A. Methods Retrospective data from the Optum’s de-identified Clinformatics Data Mart Database were used to create 3 cohorts: C1, Pre-COVID; C2, During COVID; C3, Cross-COVID (Figure 1). The completion was defined as number of PCV13 doses received within 8 months of birth, and the adherence was defined number of doses received at ACIP recommended time (@2, 4, 6 months, +/- 5 days). Univariable logistic regression was used to compare the odds of primary dose C&A in cohorts C1 and C3 vs C2 and descriptive analyses were used to explore primary dose C&A in relation to booster dose C&A. Figure 1: Study population and inclusion criteria Results A total of 172,916, 70,049, and 34,854 infants were included in C1, C2, and C3. Among infants with > 8 months of follow-up from birth (N=132,183 for C1&C3, 16,522 for C3), 3-primary dose completion was statistically significantly higher before COVID than during COVID (crude OR = 1.10, 95% CI: 1.06-1.15). The 3-primary dose adherence was also higher before COVID than during COVID (crude OR = 1.10, 95% CI: 1.05-1.15). Among infants with ≥2, 4 and 6 months of follow-up, adherence of each individual dose was consistently higher before COVID than during COVID (1st dose: OR = 1.03, 95% CI: 1.01–1.04; 2nd dose: OR = 1.04, 95% CI: 1.01 – 1.06; 3rd dose: OR = 1.12, 95% CI: 1.08 – 1.15) (Table 1). Booster dose completion was higher in infants who completed or adhered to 3 primary doses than infants who completed or adhered to only 1 or 2 primary doses (Figure 2, Overall) and booster dose C&A was generally higher before COVID than during COVID (Figure 2, Cohort 1 vs. Cohort 3). Table 1. Comparison of completion and adherence of primary dosing series per-COVID vs. during-COVID era Figure 2: Booster dose completion and adherence in relation to primary dosing completion (A) and adherence (B) Conclusion These results indicated that PCV13 full completion was statistically lower during COVID, but the magnitude of the difference in infants was not extensive. Infants who completed or adhered to all three primary doses were more likely to complete or adhere to the booster dose. Further research is warranted as structured datasets mature to capture the full time span of COVID-19 mitigation measures. Disclosures Liping Huang, MD, MA, MS, Pfizer Inc (Employee) Jennifer L Nguyen, ScD, MPH, Pfizer Inc. (Employee) Johnna Perdrizet, MPH, Pfizer Inc (Employee) Tamuno Alfred, PhD, Pfizer Inc. (Employee) Adriano Arguedas, MD, Pfizer (Employee)

NRG Oncology Survey of Monte Carlo Dose Calculation Use in US Proton Therapy Centers

Purpose/Objective(s) Monte Carlo (MC) dose calculation has appeared in primary commercial treatment-planning systems and various in-house platforms. Dual-energy computed tomography (DECT) and metal artifact reduction (MAR) techniques complement MC capabilities. However, no publications have yet reported how proton therapy centers implement these new technologies, and a national survey is required to determine the feasibility of including MC and companion techniques in cooperative group clinical trials. Materials/Methods A 9-question survey was designed to query key clinical parameters: scope of MC utilization, validation methods for heterogeneities, clinical site-specific imaging guidance, proton range uncertainties, and how implants are handled. A national survey was distributed to all 29 operational US proton therapy centers on 13 May 2019. Results We received responses from 25 centers (86% participation). Commercial MC was most commonly used for primary plan optimization (16 centers) or primary dose evaluation (18 centers), while in-house MC was used more frequently for secondary dose evaluation (7 centers). Based on the survey, MC was used infrequently for gastrointestinal, genitourinary, gynecology and extremity compared with other more heterogeneous disease sites (P < .007). Although many centers had published DECT research, only 3/25 centers had implemented DECT clinically, either in the treatment-planning system or to override implant materials. Most centers (64%) treated patients with metal implants on a case-by-case basis, with a variety of methods reported. Twenty-four centers (96%) used MAR images and overrode the surrounding tissue artifacts; however, there was no consensus on how to determine metal dimension, materials density, or stopping powers. Conclusion The use of MC for primary dose calculation and optimization was prevalent and, therefore, likely feasible for clinical trials. There was consensus to use MAR and override tissues surrounding metals but no consensus about how to use DECT and MAR for human tissues and implants. Development and standardization of these advanced technologies are strongly encouraged for vendors and clinical physicists.

Epizootic ulcerative syndrome (EUS) prevention and control measures.

In Bangladesh, CARE, an international NGO working in development with agricultural and natural resource management as an important component, operated a project funded by the European Union to test the potential of farmer participatory research as a tool to improve the agricultural productivity of farmers. As part of the project activities, participatory action research groups were formed involving farmers with interest to work on the concept. Farmers were encouraged to identify their own farming problems and, based on the identified problems, farmers were assisted to develop their own strategies to solve their problems. Epizootic ulcerative syndrome (EUS) emerged as an important problem in aquaculture for farmers practicing carp culture. Based on the available information on the subject and in consultation with experts in the subject area, treatment strategies were developed by the farmers to manage this major disease, which occurs during the winter season from October to February. Lime, salt, a combination of lime and salt in a 1:1 ratio, or ash, were identified as potential treatment measures during the first year trials. Farmers agreed to apply lime and salt at the rate of 1 kg decimal-1 (1 decimal = 40 m2) as a primary dose followed by a fortnightly application at half the initial dose until the end of the season. Ash was applied at a higher dose of 3 kg 40 m-2 as a primary dose, followed by half the initial dose until the end of the season. A control group of farmers was also maintained within the Participatory Action Research Groups (PARGs). Farmers were not given any financial support for the purchase of inputs, but they were given technical support. Though all farmers did not follow the periodic application at the agreed level of chemicals, all the farmers had made more than one application. The results obtained at the end of first year with 315 farmers were highly encouraging, with good results obtained from the application of lime, salt, or ash. In addition to disease prevention, increase in fish production was noticed by the farmers as a result of application of these inputs to the pond. Following these initial encouraging results at field level, the Institute of Aquaculture, University of Stirling, UK, provided technical and monetary support to continue the study. The results conducted with another group of 232 farmers during second year confirmed the beneficial effects of lime, salt and ash and proved their popularity. In addition to the above treatments, two new treatments involving application of neem (Azadirachta indica) stems with leaves as well as application of adequate fertilisers to ensure green colour of water were also tried. The results confirmed the efficacy of lime, salt and ash as treatment materials to prevent the disease. Though neem stems were not highly effective, farmers were able to derive some relief, but the application of fertilisers to ensure adequate plankton production gave highly encouraging results. Many of these field results could not be replicated under laboratory conditions. Furthermore, a treatment that was effective in one pond did not have a similar effect in a neighbouring pond. These varied results support the view that individual pond ecology influences the effect of treatments adopted. It is thus advisable that every farmer should experiment with the successful treatments in their own pond environment to evolve suitable procedures. Most interestingly, ash, which is commonly available to most farmers as a non-purchased input, can be effectively used to prevent the disease as well as increase fish pond productivity.

Measles Maternal Antibodies With Low Avidity Do Not Interfere With the Establishment of Robust Quantity and Quality Antibody Responses After the Primary Dose of Measles, Mumps, and Rubella Vaccine Administered at 12-Months of Age

In this study, we illustrate, for the first time, that preexisting low-avidity neutralizing measles maternal antibodies do not interfere with the development of high concentrations of high-avidity measles antibodies in children immunized at age 12 months. This suggests that the quality of measles maternal antibodies, rather than the quantity, impacts immunogenicity of primary measles immunization.

1478. Efficacy and Safety of a Booster Dose of the MenACWY-TT Vaccine Administered 10 Years After Primary Vaccination with MenACWY-TT or MenACWY-PS

Background The quadrivalent meningococcal ACWY polysaccharide tetanus toxoid conjugate vaccine (MenACWY-TT; Nimenrix) is licensed in various countries to prevent disease caused by meningococcal serogroups A, C, W, and Y. In a previous study (NCT00464815), subjects aged 11‒17 years received a primary dose of MenACWY-TT or a quadrivalent polysaccharide vaccine (MenACWY-PS). Here, we report the long-term antibody persistence of the primary dose and the immunogenicity and safety of a booster dose given 10 years after primary vaccination of subjects. Methods Participants were enrolled from the Philippines and received a booster dose of MenACWY-TT at 10 years postvaccination. Antibody persistence 10 years postprimary vaccination and immunogenicity 1 month after the booster dose were evaluated by serum bactericidal activity assays using rabbit complement (rSBA) to assess the percentages of subjects with titers ≥1:8 and ≥1:128 and geometric mean titers (GMTs) for each serogroup. Safety was assessed for the booster dose. Results Of 229 subjects enrolled in this extension study, 169 and 58 subjects in the MenACWY-TT and MenACWY-PS groups, respectively, completed the booster phase. The percentages of primary MenACWY-TT recipients with prebooster rSBA titers ≥ 1:8 and ≥ 1:128 at year 10 ranged from 71.6%‒90.7% and 64.8%‒85.2% for all serogroups, respectively, compared with 43.1%‒82.4% and 25.5%‒76.5% of primary MenACWY-PS recipients; rSBA GMTs for all serogroups were higher in the MenACWY-TT group than in the MenACWY-PS group at year 10. For the MenACWY-TT and MenACWY-PS groups, respectively, the MenACWY-TT booster dose elicited rSBA titers ≥1:8 in 100% and ≥98.0% of subjects (figure); 100% and ≥96.1% of all subjects had titers ≥1:128. For all serogroups, rSBA GMTs at 1 month after the booster dose were higher than before the booster dose. No new safety signals were observed during the booster phase. Conclusion Functional antibody responses elicited by MenACWY-TT persisted 10 years after primary vaccination; the booster dose was well tolerated and elicited robust immune responses. ClinicalTrials.gov: NCT03189745, EudraCT # 2013-001512-29. Funded by Pfizer. Disclosures All authors: No reported disclosures.

2722 B. Efficacy and Safety of a Booster Dose of the MenACWY-TT Vaccine Administered 10 Years After Primary Vaccination with MenACWY-TT or MenACWY-PS

Background The quadrivalent meningococcal ACWY polysaccharide tetanus toxoid conjugate vaccine (MenACWY-TT; Nimenrix) is licensed in various countries to prevent disease caused by meningococcal serogroups A, C, W, and Y. In a previous study (NCT00464815), subjects aged 11‒17 years received a primary dose of MenACWY-TT or a quadrivalent polysaccharide vaccine (MenACWY-PS). Here, we report the long-term antibody persistence of the primary dose and the immunogenicity and safety of a booster dose given 10 years after primary vaccination of subjects. Methods Participants were enrolled from the Philippines and received a booster dose of MenACWY-TT at 10 years postvaccination. Antibody persistence 10 years postprimary vaccination and immunogenicity 1 month after the booster dose were evaluated by serum bactericidal activity assays using rabbit complement (rSBA) to assess the percentages of subjects with titers ≥ 1:8 and ≥ 1:128 and geometric mean titers (GMTs) for each serogroup. Safety was assessed for the booster dose. Results Of 229 subjects enrolled in this extension study, 169 and 58 subjects in the MenACWY-TT and MenACWY-PS groups, respectively, completed the booster phase. The percentages of primary MenACWY-TT recipients with prebooster rSBA titers ≥ 1:8 and ≥ 1:128 at year 10 ranged from 71.6%‒90.7% and 64.8%‒85.2% for all serogroups, respectively, compared with 43.1%‒82.4% and 25.5%‒76.5% of primary MenACWY-PS recipients; rSBA GMTs for all serogroups were higher in the MenACWY-TT group than in the MenACWY-PS group at year 10. For the MenACWY-TT and MenACWY-PS groups, respectively, the MenACWY-TT booster dose elicited rSBA titers ≥ 1:8 in 100% and ≥ 98.0% of subjects (figure); 100% and ≥ 96.1% of all subjects had titers ≥ 1:128. For all serogroups, rSBA GMTs at 1 month after the booster dose were higher than before the booster dose. No new safety signals were observed during the booster phase. Conclusion Functional antibody responses elicited by MenACWY-TT persisted 10 years after primary vaccination; the booster dose was well tolerated and elicited robust immune responses. ClinicalTrials.gov NCT03189745, EudraCT # 2013-001512-29. Funded by Pfizer. Disclosures All authors: No reported disclosures.

An Empirical Transmitted EPID Dosimetry Method using a Back- Projection Algorithm

Background: The present study aimed to introduce a rapid transmission dosimetry through an electronic portal-imaging device (EPID) to achieve two-dimensional (2D) dose distribution for homogenous environments.Material and Methods: In this Phantom study, first, the EPID calibration curve and correction coefficients for field size were obtained from EPID and ionization chamber. Second, the EPID off-axis pixel response was measured, and the grey-scale image of the EPID was converted into portal dose image using the calibration curve. Next, the scattering contribution was calculated to obtain the primary dose. Then, by means of a verified back-projection algorithm and the Scatter-to-Primary dose ratio, a 2D dose distribution at the mid-plane was obtained.Results: The results obtained from comparing the transmitted EPID dosimetry to the calculated dose, using commercial treatment planning system with gamma function while there is 3% dose difference and 3mm distance to agreement criteria, were in a good agreement. In addition, the pass rates of γ < 1 was 94.89% for the homogeneous volumes.Conclusion: Based on the results, the method proposed can be used in EPID dosimetry.