Ineffectiveness of international travel restrictions to contain spread of the SARS-CoV-2 Omicron BA.1 variant: a continent-wide laboratory-based observational study from Africa (preprint)

Background: In mid-November 2021, the SARS-CoV-2 Omicron BA.1 variant was detected in Southern Africa, prompting international travel restrictions of unclear effectiveness that exacted a substantial economic toll. Methods: Amidst the BA.1 wave, we tested 13,294 COVID-19 patients in 24 African countries between mid-2021 to early 2022 for BA.1 and Delta variants using real-time reverse transcription-PCR tests. The diagnostic precision of the assays was evaluated by high-throughput sequencing in four countries. The observed BA.1 spread was compared to mobility-based mathematical simulations. Findings: By November-December 2021, BA.1 had replaced the Delta variant in all African sub-regions following a South-North gradient, with a median Rt of 2.4 up to 30 days before BA.1 became predominant. PCR-based South-North spread was in agreement with phylogeographic reconstructions relying on 939 SARS-CoV-2 genomes from GISAID. PCR-based reconstructions of country-level BA.1 predominance correlated significantly in time with the emergence of BA.1 genomic sequences on GISAID (p=0.0035, cor=0.70). First BA.1 detections in affluent settings beyond Africa were predicted adequately in time by mobility-based mathematical simulations (p<0.0001). BA.1-infected inbound travelers departing from five continents were identified in five Western countries and one Northern African country by late November/early December 2021, highlighting fast global BA.1 spread aided by international travel. Interpretation: Unilateral travel bans were poorly effective because by the time they came into effect, BA.1 was already widespread in Africa and beyond. PCR-based variant typing combined with mobility-based mathematical modelling can inform rapidly and cost-efficiently on Rt, spread to inform non-pharmaceutical interventions.

Determination of SARS-CoV-2 Variants and Seroprevalence in Accra, Ghana during the Delta-Omicron Waves (preprint)

A significant proportion of SARS-CoV-2 infections in Africa are identified as asymptomatic, facilitating the silent spread of the virus especially in populated urban cities. With the surge of the highly transmissible Omicron variant, the inclusion of asymptomatics in epidemiological surveys is key in estimating true infections and seroprevalence in the population. The aim of the study was to determine seroprevalence, active infection and circulating variants in Accra, the capital city of Ghana during the Omicron wave. The study was a cross-sectional survey conducted in 22 municipalities in December 2021. Naso-oropharyngeal swabs and serum samples were collected from 1027 individuals aged 5 years and above, for detection of infection by RT-qPCR and estimation of total antibodies using the WANTAI ELISA kit. Our results show 10% SARS-CoV-2 prevalence, with the Omicron and Delta variants accounting for 44.1% and 8.8% of infections, respectively. Omicron was most prevalent (48.9.%) among the 20–39-year-olds. Asymptomatic individuals accounted for 75.2% of infections. Seropositivity within the population was 86.8%, with the 60+ year group having significantly higher likelihood of exposure (OR 10.22: 95% CI: 3.51-29.73; p<0.001). This high seroprevalence appears to have been as a result of increased vaccination among this group (OR 2.7: 95% CI 1.78-4.09, p < 0.001). The high seropositivity of SARS-CoV-2 in the capital could be a good indication of herd immunity among the population and while the low infection rate supports the role of vaccination in reducing viral transmission.