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. 2021 Nov 19;19(1):303.
doi: 10.1186/s12916-021-02187-y.

SARS-CoV-2 exposure in Malawian blood donors: an analysis of seroprevalence and variant dynamics between January 2020 and July 2021

Jonathan Mandolo #  1 , Jacquline Msefula #  1 , Marc Y R Henrion  1   2 , Comfort Brown  1 , Brewster Moyo  1 , Aubrey Samon  3 , Thandeka Moyo-Gwete  4   5 , Zanele Makhado  4   5 , Frances Ayres  4   5 , Thopisang Motlou  4   5 , Nonkululeko Mzindle  4   5 , Newton Kalata  1 , Adamson S Muula  6 , Gaurav Kwatra  7   8   9 , Natasha Nsamala  3 , Andrew Likaka  3   10 , Thom Mfune  3 , Penny L Moore  4   5 , Bridon Mbaya  3 , Neil French  11 , Robert S Heyderman  12 , Todd Swarthout #  1   12 , Kondwani C Jambo #  13   14   15
Affiliations

SARS-CoV-2 exposure in Malawian blood donors: an analysis of seroprevalence and variant dynamics between January 2020 and July 2021

Jonathan Mandolo et al. BMC Med. .

Abstract

Background: By August 2021, the COVID-19 pandemic has been less severe in sub-Saharan Africa than elsewhere. In Malawi, there have been three subsequent epidemic waves. We therefore aimed to describe the dynamics of SARS-CoV-2 exposure in Malawi.

Methods: We measured the seroprevalence of anti-SARS-CoV-2 antibodies amongst randomly selected blood transfusion donor sera in Malawi from January 2020 to July 2021 using a cross-sectional study design. In a subset, we also assessed in vitro neutralisation against the original variant (D614G WT) and the Beta variant.

Results: A total of 5085 samples were selected from the blood donor database, of which 4075 (80.1%) were aged 20-49 years. Of the total, 1401 were seropositive. After adjustment for assay characteristics and applying population weights, seropositivity reached peaks in October 2020 (18.5%) and May 2021 (64.9%) reflecting the first two epidemic waves. Unlike the first wave, both urban and rural areas had high seropositivity in the second wave, Balaka (rural, 66.2%, April 2021), Blantyre (urban, 75.6%, May 2021), Lilongwe (urban, 78.0%, May 2021), and Mzuzu (urban, 74.6%, April 2021). Blantyre and Mzuzu also show indications of the start of a third pandemic wave with seroprevalence picking up again in July 2021 (Blantyre, 81.7%; Mzuzu, 71.0%). More first wave sera showed in vitro neutralisation activity against the original variant (78% [7/9]) than the beta variant (22% [2/9]), while more second wave sera showed neutralisation activity against the beta variant (75% [12/16]) than the original variant (63% [10/16]).

Conclusion: The findings confirm extensive SARS-CoV-2 exposure in Malawi over two epidemic waves with likely poor cross-protection to reinfection from the first on the second wave. The dynamics of SARS-CoV-2 exposure will therefore need to be taken into account in the formulation of the COVID-19 vaccination policy in Malawi and across the region. Future studies should use an adequate sample size for the assessment of neutralisation activity across a panel of SARS-CoV-2 variants of concern/interest to estimate community immunity.

Keywords: Blood donors; Malawi; SARS-CoV-2; Seroprevalence.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Overall SARS-CoV-2-adjusted seroprevalence over time superimposed on Malawi national PCR-confirmed COVID-19 cases. Black dots (together with 95% CI) are estimated seroprevalence at each time point (month), adjusted for assay sensitivity and specificity. The histograms represent confirmed national COVID-19 cases per month, including asymptomatic and symptomatic cases. The vertical dotted line defines the transition from 2020 to 2021. SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; COVID-19, coronavirus disease 2019; Ab+, positive for the detection of anti-SARS-CoV-2 receptor-binding domain (RBD) antibody
Fig. 2
Fig. 2
Flexible seroprevalence models. The model fits provide a smoothed estimate of the seroprevalence over time (January 2020 to July 2021) for each location. A Balaka. B Blantyre. C Mzuzu. D Lilongwe. The orange line is the line of best fit for the empirical data, using a smooth generalised additive model, along with light orange shading indicating 95% CI. Black dots (together with 95% CI) are estimated seroprevalence at each time point (months), adjusted for assay sensitivity and specificity. Grey dots (top and bottom of figures) show the individual-level data, which are either positive (1) or negative (0) for the detection of anti-SARS-CoV-2 receptor-binding domain (RBD) antibody
Fig. 3
Fig. 3
Seroprevalence bubble plot for the overall seroprevalence at three snapshots in time. The size of the bubble is proportional to the prevalence of samples positive for anti-SARS-CoV-2 receptor-binding domain (RBD) antibody within each location
Fig. 4
Fig. 4
Neutralisation of viral variants using the sera from the first and second epidemic waves. Anti-RBD seropositive sera from the SARS-CoV-2 epidemic waves 1 and 2 were subjected to a SARS-CoV-2 pseudovirus neutralisation assay. A Correlation of SARS-CoV-2 antibody neutralisation potency against D614G WT and beta variant. B Proportion of wave 1 or wave 2 sera with neutralisation activity against D614G WT or beta variant. The threshold of detection for the neutralisation assay is ID50 > 20. RBD, receptor-binding domain
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