Interplay of demographics, geography and COVID-19 pandemic responses in the Puget Sound region: The Vashon, Washington Medical Reserve Corps experience

Background Rural U.S. communities are at risk from COVID-19 due to
advanced age and limited access to acute care. Recognizing this, the
Vashon Medical Reserve Corps (VMRC) in King County, Washington,
implemented an all-volunteer, community-based COVID-19 response program.
 This program integrated public engagement, SARS-CoV-2 testing,
contact tracing, vaccination, and material community support, and was
associated with the lowest cumulative COVID-19 case rate in King County.
This study aimed to investigate the contributions of demographics,
geography and public health interventions to Vashon’s low COVID-19 rates.
Methods This observational cross-sectional study compares cumulative
COVID-19 rates and success of public health interventions from February
2020 through November 2021 for Vashon Island with King County (including
metropolitan Seattle) and Whidbey Island, located ~50 km north of Vashon.
To evaluate the role of demography, we developed multiple linear
regression models of COVID-19 rates using metrics of age, race/ethnicity,
wealth and educational attainment across 77 King County zip codes. To
investigate the role of remote geography we expanded the regression models
to include North, Central and South Whidbey, similarly remote island
communities with varying demographic features. To evaluate the
effectiveness of VMRC’s community-based public health measures, we
directly compared Vashon’s success of vaccination and contact tracing with
that of King County and South Whidbey, the Whidbey community most similar
to Vashon. Results Vashon’s cumulative COVID-19 case rate was 29% that of
King County overall (22.2 vs 76.8 cases/K). A multiple linear regression
model based on King County demographics found educational attainment to be
a major correlate of COVID-19 rates, and Vashon’s cumulative case rate was
just 38% of predicted (p<.05), so demographics alone do not explain
Vashon’s low COVID-19 case rate. Inclusion of Whidbey communities in the
model identified a major effect of remote geography (-49 cases/K,
p<.001), such that observed COVID-19 rates for all remote
communities fell within the model’s 95% prediction interval. VMRC’s
vaccination effort was highly effective, reaching a vaccination rate of
1500 doses/K four months before South Whidbey and King County and
maintaining a cumulative vaccination rate 200 doses/K higher throughout
the latter half of 2021 (p<.001). Including vaccination rates in
the model reduced the effect of remote geography to -41 cases/K
(p<.001). VMRC case investigation was also highly effective,
interviewing 96% of referred cases in an average of 1.7 days compared with
69% in 3.7 days for Washington Department of Health investigating South
Whidbey cases and 80% in 3.4 days for Public Health–Seattle & King
County (both p<0.001). VMRC’s public health interventions were
associated with a 30% lower case rate (p<0.001) and 55% lower
hospitalization rate (p=0.056) than South Whidbey. Conclusion While the
overall magnitude of the pre-Omicron COVID-19 pandemic in rural and urban
U.S. communities was similar, we show that island communities in the Puget
Sound region were substantially protected from COVID-19 by their
geography. We further show that a volunteer community-based COVID-19
response program was highly effective in the Vashon community, augmenting
the protective effect of geography. We suggest that Medical Reserve Corps
should be an important element of future pandemic planning.