COVID-19 Incidence Disparities Lessened After Vaccine Availability Despite Differences in Community Vaccination Coverage

A study published in a Morbidity and Mortality Weekly Report issued by the CDC indicated that communities with lower median household incomes have been disproportionally affected by COVID-19 throughout the pandemic. Compared with higher-income areas, these communities experienced higher degrees of COVID-19 incidence before the vaccine became widely available.

To get a better sense of the health disparities affecting these communities, researchers gathered community-level data on COVID-19 incidence and vaccine coverage in 81 communities around Los Angeles. Three surges in COVID-19 were observed—2 prevaccine spikes (July 2020 and January 2021) and 1 postvaccine spike (September 2021). Information was taken from the Los Angeles Times COVID-19 data repository between March 2020 and September 2021 to analyze rates of COVID-19 cases and vaccinations against varying median household incomes. Median incomes ranged from $48,000 per year to $134,000.

In both July 2020 and January 2021, the incidence of COVID-19 was higher in households with lower median income (2020: adjusted incidence rate ratio [aIRR], 6.6; 95% CI, 2.8-15.3; 2021: aIRR, 4.3; 95% CI, 1.8-9.9). However, these disparities dissipated by the postvaccine surge in September 2021 (aIRR, 0.8; 95% CI, 0.35-1.86).

Reports from the September 2021 surge revealed higher median household income was related to higher levels of community vaccination. Higher-income households registered a median community vaccination coverage of 71.5% (95% CI, 68.5%-74.4%) compared with 59.4% (95% CI, 57.6%-61.2%) in lower-income households (P < .001). COVID-19 incidence and community vaccine coverage were inversely related across all incomes. Despite overall lower levels of vaccination, however, lower-income communities experienced the highest estimated impact on incidence from the vaccine (an additional 8.1% reduction in cases for every 20% increase in community vaccination coverage).

Among the limitations listed, authors mentioned that their data do not include person-level information for more direct estimations on the influence of individual vaccination status on COVID-19 incidence by income. This limitation prevents researchers from accounting for cases of individual immunity from previous COVID-19 infection. The authors also recognize that some observations could have been dampened or inflated because it was impossible to adjust for differing use of or access to testing over time. And lastly, it is hard to generalize these results outside of Los Angeles or to other pandemic surges—especially because the vaccine affects COVID-19 variants differently.

The authors noted that in March 2021 during the initial vaccine rollout, California allocated 40% of vaccine appointments toward communities in the lower levels of the California Healthy Places Index. Although these resources aimed to offset health disparities, vaccination differences remained between higher- and lower-income communities. These findings demonstrate the continued need for improving vaccination confidence and access to help mitigate income-related health disparities.

Reference

Masterson J, Luu M, Dallas K, Daskivich L, Spiegel B, Daskivich J. Disparities in COVID-19 disease incidence by income and vaccination coverage—81 communities, Los Angeles, California, July 2020-September 2021. MMWR Morb Mortal Wkly Rep. 2023;72(26):728-731. doi:10.15585/mmwr.mm7226a5