Add new links, including to our PNAS indicators paper

Author: capnrefsmmat

content/covid19/_index.md

@@ -4,11 +4,11 @@ linkTitle: COVID-19
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-In March 2020, Delphi pivoted from seasonal epidemic forecasting to COVID-19 tracking. Since then, we’ve created and maintained the nation’s largest public repository of diverse, geographically-detailed, real-time indicators of COVID-19 activity in the U.S. Our indicators cover every rung of the severity pyramid, and are freely available through our public API or our data export tool.
+In March 2020, Delphi pivoted from seasonal epidemic forecasting to COVID-19 tracking. Since then, we’ve created and maintained the nation’s largest public repository of diverse, geographically-detailed, real-time indicators of COVID-19 activity in the U.S. Our indicators cover every rung of the severity pyramid, and are freely available through [our public API]({{< apiref "api/covidcast.html" >}}) or our [data export tool]({{< relref "covidcast/export" >}}).
 
 Several of the underlying data sources (on which these indicators are built) would not exist or be publicly available without our efforts. This includes:
 
-* A massive national daily survey we’re running in partnership with Facebook. Over 20 million Americans have answered the survey since April 2020, providing real-time insights into, e.g., self-reported symptoms, mask wearing, testing, and contacts, all broken down by various demographics.
+* A [massive national daily survey]({{< relref "covid19/ctis" >}}) we’re running in partnership with Facebook. Over 20 million Americans have answered the survey since April 2020, providing real-time insights into, e.g., self-reported symptoms, mask wearing, testing, and contacts, all broken down by various demographics.
 * An enormous database of medical insurance claims that have been de-identified in accordance with HIPAA privacy regulations, covering more than half the US population, made possible through health system partners including Change Healthcare. We use this to produce a new syndromic COVID-19 indicator based on doctor visits, and other indicators based on hospitalizations and ICU admissions.
 
-We have selected a small number of indicators to showcase in COVIDcast, a visualization system that helps place pandemic activity in geographic and temporal context. It includes a notion of correlation across time, for example, a spike in cases is often followed by a spike in hospital admissions some number of days later.
+An overview of our work and data was [published in the *Proceedings of the National Academy of Sciences*](https://doi.org/10.1073/pnas.2111452118). We have selected a small number of indicators to showcase in [COVIDcast]({{< relref "covidcast" >}}), a visualization system that helps place pandemic activity in geographic and temporal context. It includes a notion of correlation across time, for example, a spike in cases is often followed by a spike in hospital admissions some number of days later.