Chronic heat stress and recurrent dehydration from strenuous labour in hot environments are recognised drivers of acute kidney injury among agricultural workers in Mesoamerica and may contribute to Chronic Kidney Disease of Unknown Aetiology (CKDu). This study explored how members of a long-term community-based cohort in northwest Nicaragua perceive, experience and adapt to extreme heat, within the broader context of environmental and labour changes.

This qualitative study used focus group discussions with participants from a community-based cohort followed for over a decade and community members. Transcripts were analysed thematically using an interpretative approach, with trustworthiness ensured through peer debriefing, audit trails, triangulation and achievement of thematic saturation.

Rural agricultural communities in northwest Nicaragua participating in a long-term community-based cohort.

Participants were purposively sampled from a prospective community-based cohort and community members were invited to participate. Men and women across different age groups were invited. In total, 91 adults aged ≥18 years participated in 11 face-to-face focus groups, each comprising 8–11 men or women.

Themes describing experiences of heat stress, occupational risk and adaptive responses among agricultural workers.

Participants described worsening heat linked to deforestation, unsafe and inadequate water access and unrealistic production targets that prioritised output over health. In response, workers reported adaptive practices including self-paced labour, hydration routines and peer monitoring. Community solidarity and mutual aid emerged as key sources of resilience despite structural constraints.

Heat stress amplifies occupational hazards and exacerbates health inequities among marginalised agricultural workers. Integrating climate adaptation and equity into labour protections—ensuring access to clean water, adequate shade and fair workloads—can strengthen resilience in agricultural communities facing rising heat-related health risks.

SARS-CoV-2 infection provides protection against reinfection and severe COVID-19 disease; however, this protective effect may diminish over time. We assessed waning of natural immunity conferred by previous infection against severe disease and symptomatic reinfection in Brazil and Scotland.

We undertook a test-negative design study and nested case–control analysis to estimate waning of natural immunity against severe COVID-19 outcomes and symptomatic reinfection using national linked datasets. We used logistic regression to estimate ORs with 95% CIs. A stratified analysis assessed immunity during the Omicron dominant period in Brazil.

We included data from the adult populations of Brazil and Scotland from 1 June 2020 to 30 April 2022.

Severe COVID-19 was defined as hospitalisation or death. Reinfection was defined as reverse-transcriptase PCR or rapid antigen test confirmed at least 120 days after primary infection.

From Brazil, we included 30 881 873 tests and 1 301 665 severe COVID-19 outcomes, and from Scotland, we included 1 520 201 tests and 7988 severe COVID-19 outcomes. Against severe outcomes, sustained protection was observed for at least 12 months after primary SARS-CoV-2 infection with little evidence of waning: 12 months postprimary infection: Brazil OR 0.12 (95% CI 0.10 to 0.14), Scotland OR 0.03 (95% CI 0.02 to 0.04). For symptomatic reinfection, Brazilian data demonstrated evidence of waning in the 12 months following primary infection, although some residual protection remained beyond 12 months: 12 months postprimary infection: OR 0.42 (95% CI 0.40 to 0.43). The greatest reduction in risk of SARS-CoV-2 infection was in individuals with hybrid immunity (history of previous infection and vaccination), with sustained protection against severe outcomes at 12 months postprimary infection. During the Omicron dominant period in Brazil, odds of symptomatic reinfection were higher and increased more quickly over time when compared with the overall study period, although protection against severe outcomes was sustained at 12 months postprimary infection (whole study: OR 0.12 (95% CI 0.10 to 0.14); Omicron phase: OR 0.15 (95% CI 0.12 to 0.19)).

Cross-national analyses demonstrate sustained protection against severe COVID-19 disease for at least 12 months following natural SARS-CoV-2 infection, with vaccination further enhancing protection. Protection against symptomatic reinfection was lower with evidence of waning, but there remained a protective effect beyond 12 months from primary infection.