Search

The WHO Unity Studies initiative engaged low- and middle-income countries in the implementation of standardized SARS-CoV-2 sero-epidemiological investigation protocols and timely sharing of comparable results for evidence-based action. To gain a deeper understanding of the methodological challenges faced when conducting seroprevalence studies in the Africa region, we conducted unstructured interviews with key study teams in five countries. We discuss the challenges identified: participant recruitment and retention, sample frame, sample and data management, data analysis and presentation to policy makers. Potential solutions to aid future implementation include preparedness actions such as the development of new tools, robust planning and practice.

SummaryBackgroundWe aimed to systematically review the magnitude and duration of the protective effectiveness of prior infection (PE) and hybrid immunity (HE) against Omicron infection and severe disease.MethodsWe searched pre-print and peer-reviewed electronic databases for controlled studies from January 1, 2020, to June 1, 2022. Risk of bias (RoB) was assessed using the Risk of Bias In Non-Randomized Studies of Interventions (ROBINS-I)-Tool. We used random-effects meta-regression to estimate the magnitude of protection at 1-month intervals and the average change in protection since the last vaccine dose or infection from 3 months to 6 or 12 months. We compared our estimates of PE and HE to previously published estimates of the magnitude and durability of vaccine effectiveness (VE) against Omicron.FindingsEleven studies of prior infection and 15 studies of hybrid immunity were included. For prior infection, there were 97 estimates (27 at moderate RoB and 70 at serious RoB), with the longest follow up at 15 months. PE against hospitalization or severe disease was 82·5% [71·8-89·7%] at 3 months, and 74·6% [63·1-83·5%] at 12 months. PE against reinfection was 65·2% [52·9-75·9%] at 3 months, and 24·7% [16·4-35·5%] at 12 months. For HE, there were 153 estimates (78 at moderate RoB and 75 at serious RoB), with the longest follow up at 11 months for primary series vaccination and 4 months for first booster vaccination. Against hospitalization or severe disease, HE involving either primary series vaccination or first booster vaccination was consistently >95% for the available follow up. Against reinfection, HE involving primary series vaccination was 69·0% [58·9-77·5%] at 3 months after the most recent infection or vaccination, and 41·8% [31·5-52·8%] at 12 months, while HE involving first booster vaccination was 68·6% [58·8-76·9%] at 3 months, and 46·5% [36·0-57·3%] at 6 months. Against hospitalization or severe disease at 6 months, hybrid immunity with first booster vaccination (effectiveness 95·3% [81·9-98·9%]) or with primary series alone (96·5% [90·2-98·8%]) provided significantly greater protection than prior infection alone (80·1% [70·3-87·2%]), first booster vaccination alone (76·7% [72·5-80·4%]), or primary series alone (64·6% [54·5-73·6%]). Results for protection against reinfection were similar.InterpretationPrior infection and hybrid immunity both provided greater and more sustained protection against Omicron than vaccination alone. All protection estimates waned quickly against infection but remained high for hospitalisation or severe disease. Individuals with hybrid immunity had the highest magnitude and durability of protection against all outcomes, reinforcing the global imperative for vaccination.FundingWHO COVID-19 Solidarity Response Fund and the Coalition for Epidemic Preparedness Innovations.Research in contextEvidence before this studyThe global emergence and rapid spread of Omicron (B.1.1.529) variant of concern, characterized by their ability to escape immunity, has required scientists and policymakers to reassess the population protection against Omicron infection and severe disease. So far, few systematic reviews have incorporated data on Omicron, and none have examined the protection against Omicron conferred by hybrid immunity (i.e. the immunity gained from the combination of vaccination and prior infection) which is now widespread globally. While one preprint has recently reported protection from prior infection over time, no systematic review has systematically compared the magnitude and duration of vaccination, prior infection, and hybrid immunity. A large single-country study has reported that protection from either infection or hybrid immunity against Omicron infection wanes to low levels at 15 months, but is relatively stable against severe disease.Added value of this studyPrior infection and hybrid immunity both provided greater and more sustained protection against Omicron than vaccination alone. Individuals with hybrid immunity had the highest magnitude and durability of protection against all outcomes; protection against severe disease remained above 95% until the end of available follow-up at 11 months after hybrid immunity with primary series and 4 months after hybrid immunity with booster vaccination, and was sustained at these high levels of protection in projections to 12 months and 6 months, respectively.Implications of all the available evidenceThese results may serve to tailor guidance on the optimal number and timing of vaccinations. At the public health level, these findings can be combined with data on local infection prevalence, vaccination rates, and their timing. In settings with high seroprevalence, limited resources, and competing health priorities, it may be reasonable to focus on achieving high coverage rates with primary series among individuals who are at higher risk of poor outcome, as this will provide a high level of protection against severe disease for at least one year among those with prior infection. Furthermore, given the waning protection for both infection-and vaccine induced immunity against infection or reinfection, mass vaccination could be timed for roll-out prior to periods of expected increased incidence, such as the winter season. At the individual level, these results can be combined with knowledge of a person’s infection and vaccination history. A six-month delay in booster may be justified after the last infection or vaccination for individuals with a known prior infection and full primary series vaccination. Further follow-up of the protective effectiveness of hybrid immunity against hospitalization or severe disease for all vaccines is needed to clarify how much waning of protection might occur with longer duration since the last infection or vaccination. Producing estimates of protection for new variant-containing vaccines will be crucial for COVID-19 vaccine policy and decision-making bodies. Policy makers considering the use and timing of vaccinations should include the local extent of past infection, the protection conferred by prior infection or hybrid immunity, and the duration of this protection as key considerations to inform their decision-making.

IntroductionEstimating COVID-19 cumulative incidence in Africa remains problematic due to challenges in contact tracing, routine surveillance systems and laboratory testing capacities and strategies. We undertook a meta-analysis of population-based seroprevalence studies to estimate SARS-CoV-2 seroprevalence in Africa to inform evidence-based decision making on public health and social measures (PHSM) and vaccine strategy.MethodsWe searched for seroprevalence studies conducted in Africa published 1 January 2020–30 December 2021 in Medline, Embase, Web of Science and Europe PMC (preprints), grey literature, media releases and early results from WHO Unity studies. All studies were screened, extracted, assessed for risk of bias and evaluated for alignment with the WHO Unity seroprevalence protocol. We conducted descriptive analyses of seroprevalence and meta-analysed seroprevalence differences by demographic groups, place and time. We estimated the extent of undetected infections by comparing seroprevalence and cumulative incidence of confirmed cases reported to WHO.PROSPERO: CRD42020183634.ResultsWe identified 56 full texts or early results, reporting 153 distinct seroprevalence studies in Africa. Of these, 97 (63%) were low/moderate risk of bias studies. SARS-CoV-2 seroprevalence rose from 3.0% (95% CI 1.0% to 9.2%) in April–June 2020 to 65.1% (95% CI 56.3% to 73.0%) in July–September 2021. The ratios of seroprevalence from infection to cumulative incidence of confirmed cases was large (overall: 100:1, ranging from 18:1 to 954:1) and steady over time. Seroprevalence was highly heterogeneous both within countries—urban versus rural (lower seroprevalence for rural geographic areas), children versus adults (children aged 0–9 years had the lowest seroprevalence)—and between countries and African subregions.ConclusionWe report high seroprevalence in Africa suggesting greater population exposure to SARS-CoV-2 and potential protection against COVID-19 severe disease than indicated by surveillance data. As seroprevalence was heterogeneous, targeted PHSM and vaccination strategies need to be tailored to local epidemiological situations.

In addition to diarrheal disease risk, lack of access to safe water may have other indirect effects throughout one’s life, such as school and workplace absenteeism, leading to less economic productivity. In contexts with scarce resources and unsafe drinking water, household water treatment and safe storage options such as the Biosand filter (BSF) allows households to directly reduce contamination and increase the quality of their drinking water. This study aimed to develop an understanding of perceived community acceptability and feasibility related to pre- and post-implementation of a BSF pilot project in rural Maasai households in the Ngorongoro Conservation Area (NCA), Tanzania. The study was guided by the Integrated Behavioral Model for Water Sanitation and Hygiene interventions (IBM-WASH) to understand the various factors influencing end-user perceptions of the BSF. In-depth interviews, group discussions and think tanks were conducted among a cross-section of community members, stakeholders, and other actors from May 2016 to September 2017. The data were analyzed using a thematic content analysis approach. A range of perceived contextual, technological, and psychosocial factors were found to potentially affect the acceptability and feasibility of BSF adoption in the NCA, highlighting the complex layers of influences in the setting. Whilst the BSF is seemingly an accepted option to treat water within the NCA, the community identified key barriers that may lower BSF adoption. The application of the IBM-WASH model served as a useful framework for evaluating the introduction of the BSF, identifying insights into contextual, technological, and psychosocial community factors.

BackgroundMany studies report the seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies. We aimed to synthesize seroprevalence data to better estimate the level and distribution of SARS-CoV-2 infection, identify high-risk groups, and inform public health decision making.MethodsIn this systematic review and meta-analysis, we searched publication databases, preprint servers, and grey literature sources for seroepidemiological study reports, from January 1, 2020 to December 31, 2020. We included studies that reported a sample size, study date, location, and seroprevalence estimate. We corrected estimates for imperfect test accuracy with Bayesian measurement error models, conducted meta-analysis to identify demographic differences in the prevalence of SARS-CoV-2 antibodies, and meta-regression to identify study-level factors associated with seroprevalence. We compared region-specific seroprevalence data to confirmed cumulative incidence. PROSPERO: CRD42020183634.ResultsWe identified 968 seroprevalence studies including 9.3 million participants in 74 countries. There were 472 studies (49%) at low or moderate risk of bias. Seroprevalence was low in the general population (median 4.5%, IQR 2.4–8.4%); however, it varied widely in specific populations from low (0.6% perinatal) to high (59% persons in assisted living and long-term care facilities). Median seroprevalence also varied by Global Burden of Disease region, from 0.6% in Southeast Asia, East Asia and Oceania to 19.5% in Sub-Saharan Africa (pDiscussionMost of the population remains susceptible to SARS-CoV-2 infection. Public health measures must be improved to protect disproportionately affected groups, including racial and ethnic minorities, until vaccine-derived herd immunity is achieved. Improvements in serosurvey design and reporting are needed for ongoing monitoring of infection prevalence and the pandemic response.

BackgroundMany studies report the seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies. We aimed to synthesize seroprevalence data to better estimate the level and distribution of SARS-CoV-2 infection, identify high-risk groups, and inform public health decision making.MethodsIn this systematic review and meta-analysis, we searched publication databases, preprint servers, and grey literature sources for seroepidemiological study reports, from January 1, 2020 to December 31, 2020. We included studies that reported a sample size, study date, location, and seroprevalence estimate. We corrected estimates for imperfect test accuracy with Bayesian measurement error models, conducted meta-analysis to identify demographic differences in the prevalence of SARS-CoV-2 antibodies, and meta-regression to identify study-level factors associated with seroprevalence. We compared region-specific seroprevalence data to confirmed cumulative incidence. PROSPERO: CRD42020183634.ResultsWe identified 968 seroprevalence studies including 9.3 million participants in 74 countries. There were 472 studies (49%) at low or moderate risk of bias. Seroprevalence was low in the general population (median 4.5%, IQR 2.4-8.4%); however, it varied widely in specific populations from low (0.6% perinatal) to high (59% persons in assisted living and long-term care facilities). Median seroprevalence also varied by Global Burden of Disease region, from 0.6 % in Southeast Asia, East Asia and Oceania to 19.5% in Sub-Saharan Africa (pDiscussionMost of the population remains susceptible to SARS-CoV-2 infection. Public health measures must be improved to protect disproportionately affected groups, including racial and ethnic minorities, until vaccine-derived herd immunity is achieved. Improvements in serosurvey design and reporting are needed for ongoing monitoring of infection prevalence and the pandemic response.FundingPublic Health Agency of Canada through the COVID-19 Immunity Task Force.

Background An outbreak of highly pathogenic avian influenza (HPAI) between 2004 and 2006 resulted in the culling of 45 million birds, and has jeopardised sustainable agricultural production in southeast Asia. HPAI is highly virulent, and small-scale farms present a high-risk environment for disease transmission between animals and humans. The purpose of this study was to investigate how attitudes towards HPAI influence biosecurity mitigation behaviours such as water source management and sanitation on small-scale farms in Vietnam. Methods We used a participatory approach that included representation from farmers, government, academia, and industry. We collected cross-sectional data on demographics, farm level production, and attitudes and preferences with respect to HPAI and mitigation strategies in north and south Vietnam (Thai Binh and An Giang Provinces, respectively). A stratified randomised selection of 600 small-scale mixed livestock, crop, and fish farmers were interviewed using questionnaires and in-person interviews. We calculated participant numbers using standard epidemiological sample size formulae with α=0·05. The study was approved by Canadian and Vietnamese ethics boards and participants provided verbal informed consent. Logit regression analysis was used to examine the relation between factors influencing HPAI attitudes and behaviours. Further correlation analysis is under investigation, including Pearson correlation and principal component analysis. Findings Preliminary results show that half the farmers (51%, n=306) did not treat their water according to UN Food and Agriculture Organization guidelines, and fewer than 7% (n=40) said they would report a suspected HPAI case because of the cost and inconvenience of doing so. However, those farmers who expressed concern about HPAI were more likely to practise mitigation behaviours (p=0·034). Interpretation These preliminary analyses indicate that biosecurity guidelines may not be consistent with management styles of small-scale farms in Vietnam, but also indicate cause for concern for controlling HPAI on such farms. These results should be of interest to public health and policy authorities addressing HPAI mitigation. Our results may not be generalisable to all small-scale farmers in Vietnam because water sources and farming strategies vary across communes. Funding Grand Challenges Canada (Grant Number 0231-01 Stars in Global Health Round 4) and IDRC, Ottawa.