Which people are the most vulnerable to both heat stress and COVID-19?

Answer

All people can potentially fall ill to both heat stress and COVID-19 if exposed. However, COVID-19 has further amplified the physiological and social susceptibility of many vulnerable groups in hot weather.

People who are considered the most vulnerable to both COVID-19 and high ambient heat are:

Older people (>65 years and especially >85years);
People with underlying health conditions, including cardiovascular disease, pulmonary disease, kidney disease, diabetes / obesity, mental health issues (psychiatric disorders, depression);
Essential workers who work outdoors during the hottest times of the day or who work in places that are not temperature controlled;
Health workers and auxiliaries wearing personal protective equipment;
Pregnant women;
People living in nursing homes or long-term care facilities, especially without adequate cooling and ventilation;
People who are marginalized and isolated (experiencing homelessness, migrants with language barriers, old people living alone) and those with low income or inadequate housing, including informal settlements;
People on medication: some medication for the diseases listed above impairs thermoregulation. The impact of treatment for COVID-19 is currently unknown but should be monitored to assess any additional vulnerability.
People who have, or are recovering from, COVID-19 (which can be associated with acute kidney injury).
People in prison, or residential institutions especially if cooling measures are not in place.

What does this mean?

Preventive care must be prioritized in these most vulnerable populations. The additional strain imposed by heat stress on top of a suboptimal immune function in some people will further weaken their immunity against COVID-19. In addition, COVID-19 prevention measures, such as shelter in place, may exacerbate isolation and vulnerability to extreme heat. The social networks of many of these groups of people may not be available due to COVID-19, leaving them even more vulnerable. Issuing guidance on staying safe, such as how to stay cool at home, is critically important.

What can be done?

Ensure that they know how to keep their home cool, and themselves cool before the temperatures start to rise. (See Q&A on low-tech residential cooling options)
Consider using telephone systems for daily check-ins with the most vulnerable during a heatwave to reduce the need for face-to-face interactions due to COVID-19. In some places, telephone systems are already used to alert the most vulnerable of a forecasted heatwave. Social service partners, general practitioners and local authorities can help with setting up a system. If there is a system already in place, consider advertising it to increase enrolment.
Review plans for in-home safety checks of the most vulnerable during a heatwave in the context of COVID-19, ensuring the health and safety of outreach staff and volunteers through training and the provision of personal protective equipment (PPE).
Coordinate with formal and informal social service systems to identify vulnerable individuals and reach them more effectively with key messages (See Q&A on social services).
Social safety net programmes can be reviewed and expanded to support at-home cooling strategies for the most vulnerable people. For example, energy subsidies could be provided to at-risk households to ensure they can afford home cooling measures.
Note that health workers wearing PPE will also be more vulnerable to heat stress (See Q&A on PPE and heat stress).

Evidence

Prevalent comorbidities among COVID-19 patients include hypertension, cardiovascular diseases, diabetes mellitus, chronic obstructive pulmonary disease (COPD), malignancy, and chronic kidney disease and cases with these comorbidities are more severe (Emami, Javanmardi, Pirbonyeh, & Akbari, 2020; Hu et al., 2020; Yang et al., 2020). These same chronic diseases are risk factors during heatwaves (Benmarhnia, Deguen, Kaufman, & Smargiassi, 2015). Further research has shown higher COVID-19 mortality rates among the elderly and subjects with multi-chronic conditions (Shahid et al., 2020), thus making the elderly population at an even greater risk from heat. There is strong evidence for old age as a risk factor for heat-related health impacts, with an increasing trend in risk as age progresses from 65 years to 85 years (Benmarhnia et al., 2015). The elderly are at particular risk due to impaired thermoregulatory mechanisms, chronic dehydration, chronic diseases, especially cardio-pulmonary disease and diabetes, use of medications, disability and higher likelihood of social isolation (Basu et al., 2009; Bunker et al., 2016; R Sari Kovats & Hajat, 2008; Mayrhuber et al., 2018).

Low income, living alone and being socially isolated (Benmarhnia et al., 2015; Michelozzi et al., 2005; Semenza, McCullough, Flanders, McGeehin, & Lumpkin, 1999) are associated to increased mortality during heat waves. Patients with cardiovascular and respiratory disease and other chronic diseases are at greater risk during extreme heat (Bhaskaran, Hajat, & Smeeth, 2011; Sun et al., 2016; Yu et al., 2012; Cheng et al., 2019; Gronlund, Zanobetti, Schwartz, Wellenius, & O’Neill, 2014) as are residents of nursing homes and long term care facilities without adequate cooling and ventilation (Klenk, Becker, & Rapp, 2010; R S Kovats, Johnson, & Griffith, 2006; Stafoggia et al., 2006). In terms of heat-related hazards for health workers and auxiliaries, wearing personal protective equipment can increase heat stress (Honda & Iwata, 2016; Potter, Gonzalez, & Xu, 2015; Tharion et al., 2013).

References

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