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Background: Despite the disproportionate morbidity and mortality experienced by American Indian and Alaska Native (AI/AN) persons during the coronavirus disease 2019 (COVID-19) pandemic, few studies have reported vaccine effectiveness (VE) estimates among these communities. Methods: We conducted a test-negative case-control analysis among AI/AN persons aged ≥12 years presenting for care from January 1, 2021, through November 30, 2021, to evaluate the effectiveness of mRNA COVID-19 vaccines against COVID-19-associated outpatient visits and hospitalizations. Cases and controls were patients with ≥1 symptom consistent with COVID-19-like illness; cases were defined as those test-positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and controls were defined as those test-negative for SARS-CoV-2. We used unconditional multivariable logistic regression to estimate VE, defined as 1 minus the adjusted odds ratio for vaccination among cases vs controls. Results: The analysis included 207 cases and 267 test-negative controls. Forty-four percent of cases and 78% of controls received 2 doses of either BNT162b2 or mRNA-1273 vaccine. VE point estimates for 2 doses of mRNA vaccine were higher for hospitalized participants (94.6%; 95% CI, 88.0-97.6) than outpatient participants (86.5%; 95% CI, 63.0-95.0), but confidence intervals overlapped. Conclusions: Among AI/AN persons, mRNA COVID-19 vaccines were highly effective in preventing COVID-associated outpatient visits and hospitalizations. Maintaining high vaccine coverage, including booster doses, will reduce the burden of disease in this population.
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PURPOSE: We assessed 18-month cumulative mother-to-child HIV transmission (MTCT) risk and risk factors for no antiretroviral medication use during pregnancy among adolescent, young women, and adult mothers in Zimbabwe. METHODS: We analyzed data from a prospective survey of 1,171 mother-infant pairs with HIV-exposed infants aged 4-12 weeks who were recruited from 151 immunization clinics from February to August 2013. HIV-exposed infants were followed until diagnosed with HIV, death, or age 18 months. Findings were weighted and adjusted for complex survey design and nonresponse. RESULTS: The 18-month cumulative MTCT risk was highest among adolescent aged ≤19 years (12%) followed by young women aged 20-24 years (7.5%) and adult women aged ≥25 years (6.9%). Across these groups, more than 94% had ≥1 antenatal care visit by 21 weeks of gestation, more than 95% had ≥1 HIV test, and more than 98% knew their HIV status. Of known HIV-positive mothers, maternal antiretroviral medication coverage during pregnancy was 76.8% (95% confidence interval: 65.1-85.5), 83.8% (78.6-87.9), and 87.8% (84.6-90.4) among adolescent, young women, and adult mothers, respectively. Among HIV-positive mothers diagnosed prenatally, the adjusted odds ratio of no ARV use during pregnancy was increased among those who had no antenatal care attendance (adjusted odds ratio: 7.7 [3.7-16.0]), no HIV testing (7.3 [2.3-23.5]), no prepartum CD4 count testing (2.1 [1.3-3.4]), and maternal HIV identification during pregnancy (2.9 [1.8-4.8]). Age was not a risk factor. CONCLUSIONS: With similar coverage of prevention of MTCT services, the 18-month cumulative MTCT risk was higher among adolescents and young women, compared with adults. Additional research should examine the causes to develop targeted interventions.