ABSTRACT
BackgroundIn low- and middle-income countries where SARS-CoV-2 testing is limited, seroprevalence studies can characterise the scale and determinants of the pandemic, as well as elucidate protection conferred by prior exposure. MethodsWe conducted repeated cross-sectional serosurveys (July 2020 - November 2021) using residual plasma from routine convenient blood samples from patients with non-COVID-19 conditions from Cape Town, South Africa. SARS-CoV-2 anti-nucleocapsid antibodies and linked clinical information were used to investigate: (1) seroprevalence over time and risk factors associated with seropositivity, (2) ecological comparison of seroprevalence between subdistricts, (3) case ascertainment rates, and (4) the relative protection against COVID-19 associated with seropositivity and vaccination statuses, to estimate variant disease severity. FindingsAmong the subset sampled, seroprevalence of SARS-CoV-2 in Cape Town increased from 39.2% in July 2020 to 67.8% in November 2021. Poorer communities had both higher seroprevalence and COVID-19 mortality. Only 10% of seropositive individuals had a recorded positive SARS-CoV-2 test. Antibody positivity before the start of the Omicron BA.1 wave (28 November 2021) was strongly protective for severe disease (adjusted odds ratio [aOR] 0.15; 95%CI 0.05-0.46), with additional benefit in those who were also vaccinated (aOR 0.07, 95%CI 0.01-0.35). InterpretationThe high population seroprevalence in Cape Town was attained at the cost of substantial COVID-19 mortality. At the individual level, seropositivity was highly protective against subsequent infections and severe COVID-19. FundingWellcome Trust, National Health Laboratory Service, the Division of Intramural Research, NIAID, NIH (ADR) and Western Cape Government Health. Research in contextO_ST_ABSEvidence before this studyC_ST_ABSIn low- and middle-income countries where SARS-CoV-2 testing is limited, seroprevalence studies can help describe the true extent of the pandemic. Infection from Omicron was associated with less severe disease in South Africa, but it is unclear whether this was due to a decrease in virulence of the variant or if prior infection provided protection. Added value of this studyThe seroprevalence data nested within a population cohort enabled us to assess differential case ascertainment rates, as well as to examine the contribution of both natural and vaccine-induced immunity in protecting communities against infections and severe disease with different SARS-CoV-2 variants. Implications of the available evidenceInequality and differential access to resources resulted in poorer communities having higher seroprevalence and COVID-19 death rates, with lower case ascertainment rates. Antibody positivity provided strong protection against an immune escape variant like Omicron but came at a high mortality cost.
ABSTRACT
ObjectiveWe aimed to compare clinical severity of Omicron BA.4/BA.5 infection with BA.1 and earlier variant infections among laboratory-confirmed SARS-CoV-2 cases in the Western Cape, South Africa, using timing of infection to infer the lineage/variant causing infection. MethodsWe included public sector patients aged [≥]20 years with laboratory-confirmed COVID-19 between 1-21 May 2022 (BA.4/BA.5 wave) and equivalent prior wave periods. We compared the risk between waves of (i) death and (ii) severe hospitalization/death (all within 21 days of diagnosis) using Cox regression adjusted for demographics, comorbidities, admission pressure, vaccination and prior infection. ResultsAmong 3,793 patients from the BA.4/BA.5 wave and 190,836 patients from previous waves the risk of severe hospitalization/death was similar in the BA.4/BA.5 and BA.1 waves (adjusted hazard ratio [aHR] 1.12; 95% confidence interval [CI] 0.93; 1.34). Both Omicron waves had lower risk of severe outcomes than previous waves. Prior infection (aHR 0.29, 95% CI 0.24; 0.36) and vaccination (aHR 0.17; 95% CI 0.07; 0.40 for boosted vs. no vaccine) were protective. ConclusionDisease severity was similar amongst diagnosed COVID-19 cases in the BA.4/BA.5 and BA.1 periods in the context of growing immunity against SARS-CoV-2 due to prior infection and vaccination, both of which were strongly protective.
ABSTRACT
ObjectivesWe aimed to compare COVID-19 outcomes in the Omicron-driven fourth wave with prior waves in the Western Cape, the contribution of undiagnosed prior infection to differences in outcomes in a context of high seroprevalence due to prior infection, and whether protection against severe disease conferred by prior infection and/or vaccination was maintained. MethodsIn this cohort study, we included public sector patients aged [≥]20 years with a laboratory confirmed COVID-19 diagnosis between 14 November-11 December 2021 (wave four) and equivalent prior wave periods. We compared the risk between waves of the following outcomes using Cox regression: death, severe hospitalization or death and any hospitalization or death (all [≤]14 days after diagnosis) adjusted for age, sex, comorbidities, geography, vaccination and prior infection. ResultsWe included 5,144 patients from wave four and 11,609 from prior waves. Risk of all outcomes was lower in wave four compared to the Delta-driven wave three (adjusted Hazard Ratio (aHR) [95% confidence interval (CI)] for death 0.27 [0.19; 0.38]. Risk reduction was lower when adjusting for vaccination and prior diagnosed infection (aHR:0.41, 95% CI: 0.29; 0.59) and reduced further when accounting for unascertained prior infections (aHR: 0.72). Vaccine protection was maintained in wave four (aHR for outcome of death: 0.24; 95% CI: 0.10; 0.58). ConclusionsIn the Omicron-driven wave, severe COVID-19 outcomes were reduced mostly due to protection conferred by prior infection and/or vaccination, but intrinsically reduced virulence may account for an approximately 25% reduced risk of severe hospitalization or death compared to Delta.
ABSTRACT
IntroductionThe outbreak of novel coronavirus disease 2019 (COVID-19) caught the world off guard in the first quarter of the year 2020. To stem the tide of this pandemic, the development, testing, and pre-licensure approval for emergency use of some COVID 19 vaccine candidates were accelerated. This led to raised public concern about their safety and efficacy, compounding the challenges of vaccine hesitancy which was already declared one of the top ten threats to global health in the year 2019. The onus of managing and administering these vaccines to a skeptical populace when they do become available rests mostly on the shoulders of healthcare workers (HCWs). Therefore, the vaccine confidence levels of HCWs becomes critical to the success of vaccination endeavors, especially COVID 19 vaccination. This proposed study aims to estimate the level of vaccine confidence and the intention to receive a COVID 19 vaccine among future HCWs and their trainers at a specific university in Cape Town, South Africa, and to identify any vaccination concerns early for targeted intervention. Methods and analysisAn online survey will be distributed to current staff and students of an academic institution for HCWs. The survey questionnaire will consist of a demographic questions section consisting of six items and a vaccine confidence section comprising six items in Likert scale format. A multinomial logistic regression model will be employed to identify factors associated with vaccine confidence and intention. The strength of association will be assessed using odds ratio and its 95% confidence interval. Statistical significance will be defined at a p-value <0.05. Ethics and disseminationEthics approval has been obtained for the study from Stellenbosch University (HREC Reference # S19/01/014 (PhD)). The results will be shared with relevant health authorities, presented at conferences, and published in a peer-reviewed journal. ARTICLE SUMMARYO_ST_ABSStrengths and limitations of this studyC_ST_ABS{blacktriangleright} The proposed study will generate baseline knowledge of the vaccine confidence among future healthcare workers and their trainers in its specific context. {blacktriangleright}It will contribute to addressing the knowledge gap about the intention to receive a COVID 19 vaccine among health care workers in Africa. {blacktriangleright}It will enable the early identification of vaccine concerns of healthcare workers while they are still in training and assist in informing tailored measures to address them. {blacktriangleright}A limitation of the study is the possibility of a low response rate which is an inherent challenge of online surveys.
