article · Nature Communications
Real-world evidence on immune responses to the two-dose AZD1222 COVID-19 vaccine in African populations has been scarce. An evaluation of baseline SARS-CoV-2 exposure and vaccine-induced neutralising antibodies was conducted in cohorts of Nigerian healthcare workers and a Ghanaian community pre- and post-vaccination. Pre-vaccination antibody screening indicated substantial prior exposure in both cohorts. Following two doses of the vaccine, participants with prior exposure demonstrated significantly higher neutralising antibody titres. Despite evidence of breakthrough infections in sixteen percent of evaluated participants, the vaccine proved immunogenic across both groups. However, neutralising antibody levels subsequently waned, notably among individuals without prior infection where a twenty percent waning rate was documented. These findings show that two doses elicit protective immune responses in populations with high background exposure, while declining antibody levels highlight the necessity of booster doses in African settings.
Understanding how populations in West Africa respond to COVID-19 vaccines is crucial for guiding public health interventions. High prior exposure boosts antibody levels following vaccination, but waning immunity demonstrates that hybrid immunity alone is insufficient. This evidence directly supports the deployment of booster doses and informs national vaccination strategies across the region.
The findings provide applied real-world clinical data to assist vaccine developers, healthcare providers, and public health agencies in designing booster schedules. The identified antibody waning also indicates a need for multi-marker diagnostic assays to reliably detect past infections in clinical or surveillance settings. These applications represent applied clinical research directly relevant to regional immunisation programmes and diagnostic protocol design.
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Real-world data on vaccine-elicited neutralising antibody responses for two-dose AZD1222 in African populations are limited. We assessed baseline SARS-CoV-2 seroprevalence and levels of protective neutralizing antibodies prior to vaccination rollout using binding antibodies analysis coupled with pseudotyped virus neutralisation assays in two cohorts from West Africa: Nigerian healthcare workers (n = 140) and a Ghanaian community cohort (n = 527) pre and post vaccination. We found 44 and 28% of pre-vaccination participants showed IgG anti-N positivity, increasing to 59 and 39% respectively with anti-receptor binding domain (RBD) IgG-specific antibodies. Previous IgG anti-N positivity significantly increased post two-dose neutralizing antibody titres in both populations. Serological evidence of breakthrough infection was observed in 8/49 (16%). Neutralising antibodies were observed to wane in both populations, especially in anti-N negative participants with an observed waning rate of 20% highlighting the need for a combination of additional markers to characterise previous infection. We conclude that AZD1222 is immunogenic in two independent West African cohorts with high background seroprevalence and incidence of breakthrough infection in 2021. Waning titres post second dose indicates the need for booster dosing after AZD1222 in the African setting despite hybrid immunity from previous infection.
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DOI: 10.1038/s41467-022-33792-x
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