According to our temporal analysis of workers who died of COVID-19 in California, male sex; being aged 50–64 years; being Native Hawaiian or Latino or African American race/ethnicity; having an education level of high school or less; and not being married were associated with a higher COVID-19 mortality rate in all waves. While disparities by sex, race and foreign-born status narrowed in Waves 4 and 5, with the largest decline occurring from Wave 3 to 4, there were minimal changes in disparities by age, education level and marital status across waves.
Sex disparities in COVID-19 incidence and mortality among men have been attributed to underlying social and contextual factors such as preexisting health status, health behaviors, occupation and social experience.3 Once tested, men were more likely to be hospitalized and to suffer severe outcomes18, possibly due to underlying health conditions such as cardiovascular disease, which are more common in men.19,20 One study found that despite similar proportions of males and females with confirmed COVID-19, male patients had more severe health outcomes, more hospitalizations and more deaths than female patients.21 However, vaccination likely prevented adverse outcomes and may have narrowed the gap in COVID-19 mortality rates between men and women in later waves of the pandemic. Societal and cultural differences in the implementation of mitigation measures over time may also play a role in the change in disparities by sex. Earlier in the pandemic, women reported taking more precautions than men, such as cancelling travel and large gatherings, stocking food and household supplies and staying home to reduce their exposure.22 Women also left the workforce in greater numbers than men during the pandemic to care for children or family members in need.23 Differences in the implementation of preventive behaviors by sex as well as the associated impact of these measures on sex disparities may have decreased in the periods where restrictions were lifted and vaccinations were available, providing protection for both male and female workers.
Racial disparities were apparent early in the pandemic and may be attributed to greater structural inequities, a greater prevalence of comorbidities and the impact of social determinants of health, such as overrepresentation of people of color in low-wage jobs.6,24,25 Similar to our findings, other studies have shown that racial disparities declined in later stages of the pandemic,26,27 which could be due to increasing vaccine uptake among racial groups over time. One study showed that COVID-19 vaccine hesitancy decreased by one-third from January to May 2021 (waves 3 to 4), with relatively large decreases in hesitancy among Black, Pacific Islander and Hispanic participants.27 In our analysis, these racial groups had the highest MRRs compared to Whites in earlier waves; a substantial increase in vaccine uptake among these groups could explain the declining disparities by race we observed in later waves of the pandemic.
Disparities by race and foreign-born status may be closely related, as a majority of the foreign-born workers (57.7%) were Latino.28 This may therefore partly explain the similar pattern of narrowing in disparities by race and by foreign-born status. Previous studies also showed that immigrants were disproportionately affected by COVID-19, particularly earlier during the pandemic.29,30 One study found that the majority of US-born mortalities were among nonworking residents of long-term care facilities and occurred late in 2020, while foreign-born mortalities occurred outside of residential institutions and earlier during the pandemic.29 Immigrants were overrepresented in multiple sectors that were frontline and most affected by the pandemic.30,31 Less stable employment conditions, limited teleworking possibilities and obstacles to health services, such as lack of accurate information and language barriers, were among the factors that contributed to the disproportionate impact on foreign-born individuals at the beginning of the pandemic.30,31 Improvements in COVID-19 prevention and care later in the pandemic (including better information, increased testing, vaccinations and interventions) may have helped reduce disparities caused by immigration status, as the evidence for long-term disparities is mixed.30 Our results also showed that, compared to US-born workers, foreign-born workers were more than three times more likely to die from COVID-19 earlier during the pandemic (in Wave 1) and 12% less likely to die in Wave 5.
Like previous studies, we found that older individuals (50 to 64 years) were more likely to die from COVID-19 than younger individuals2,4, likely because a greater incidence of comorbidities and weakened immune systems contribute to more severe outcomes.4 Compared to that in individuals aged 18–29 years, the high mortality rate in Wave 3 for those aged 50 to 64 years may be due to the overall increase in infection during this period. As infection rates rose from the end of 2020 through early 2021, the older population had higher mortality rates than younger individuals,2 therefore increasing the disparity between older and younger individuals. The large decline in the MRR for older individuals between Waves 3 and 4 (delta variant) may be due to the vaccinations introduced during this period. Since older individuals were prioritized for receiving COVID-19 vaccinations earlier than the general population,32 early protection would lower mortality rates among older worker populations and overall relative disparity compared to younger individuals.
Our findings showed that individuals with an education level of high school or less had consistently greater COVID-19 mortality rates throughout the pandemic, similar to the findings of another study in which excess COVID-19 mortality decreased as educational level increased.5 The high mortality rate among those with less education could be due to upstream socioeconomic factors that create few work opportunities and lead to lower income levels and precarious social status, all of which can in turn affect SARS-CoV-2 exposure, limit access to healthcare and increase the risk of comorbidities.5 Persons working in low-wage jobs have less ability to telework, increasing the chance for workplace exposure but fewer opportunities for paid sick leave.33 The disparities by education may also be mediated by occupation and industry, as education is a strong predictor of occupation and type of occupation is associated with COVID-19 mortality.7,25 A substantial proportion of frontline workers, such as those in Production, Transportation and Farming occupations, comprised less educated and disadvantaged minority workers34 who suffered excess COVID-19 mortality during the pandemic.25 Disparities by education level slightly declined during the largest peak in mortality (Wave 3) and increased in the vaccination era (Wave 4). The disproportionate mortality among less educated groups may have been influenced by vaccine hesitancy and access and lower vaccination levels perpetuated through later waves.35 Disparities by education level and occupation have persisted during the pandemic despite the availability of COVID-19 vaccines,5,25 as shown by trends that differed from those observed for race, sex and foreign-born status, which showed continuous narrowing in later waves.
Throughout all waves, we found that individuals who were not married had higher mortality rates than those who were married. Previous studies have shown that being unmarried is associated with adverse COVID-19 outcomes compared to being married 36,37, which parallels the overall higher death rate for unmarried persons, particularly men.38
These findings provide additional evidence that pandemics are mirroring and exacerbating preexisting inequalities and social disadvantage.39 The disproportionate COVID-19 mortality among certain populations may reflect factors that increase exposure to COVID-19, such as overrepresentation in low-wage jobs and the essential workforce; inadequate safety and mitigation policies in the workplace; and differential vulnerability to severe outcomes resulting from underlying health conditions, comorbidities, and socioeconomic status. Prevention policies that address different levels of these gaps could help narrow disparities by worker characteristics. These trends in disparities suggest that policies and interventions may have helped buffer against some of these disparities later in the pandemic but may not have been enough to eliminate them and may therefore indicate remaining gaps. Further studies could be useful for evaluating the role of specific interventions in reducing disparities in COVID-19 outcomes.
Limitations of this study include the potential presence of residual confounding, the potential for misclassification and a lack of data on key factors that may have impacted the trends in worker disparities. First, the path from worker characteristics to SARS-CoV-2 exposure to COVID-19 mortality is complex and may be affected, mediated, modified or confounded by different biological, individual, societal or environmental factors.40 Therefore, residual confounding likely occurred even though we adjusted for covariates identified as confounders. Second, there could be misclassification of demographic characteristics as well as outcomes, particularly earlier during the pandemic, when undiagnosed COVID-19 fatalities may have been reported as non-COVID-19 deaths.41 Inequities in testing earlier during the pandemic may have contributed to differential diagnoses among subgroups of the population42, which may have led to underreporting of COVID-19 mortality and decreased accuracy among certain groups early in the pandemic. However, given that our data include all COVID-19 mortality among the worker population in California during the specified period, we expect the effect of differential underreporting on our estimates to be small. Finally, we did not include data on workers’ vaccination status, which may have had a substantial impact on the patterns of disparities observed later in the pandemic. Since we included all California workers and COVID-19 decedents eligible for inclusion, our study is generalizable to California and states with similar worker populations.