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Key Epidemiology Concepts

Some Core Vocabulary

The method by which the disease causing microorganism infects or moves from one individual to another. COVID-19 has two known transmission vectors, airborne droplets (when healthy individuals encounter the small particles emitted by someone coughing or sneezing) and indirect physical contact (when healthy individuals touch a contaminated surface or object, occasionally called a fomite and then touch their face).

The expected number of cases directly attributable to one case in a population where all individuals are susceptible to infection. This number assumes that no individual in a population is immune (either through natural causes or vaccination) and that there is an absence of additional public health measures. Roughly speaking, a disease with R0 above one means that an infected individual will infect more than one additional person and the disease will spread in that population. Diseases with R0 below one (which can occur naturally or be achieved with public health interventions) will infect on average fewer than one additional person, and that disease will start to decline in that population. The basic reproduction number is not a biological constant or inherent property of a pathogen because it is affected by environmental conditions and the behavior of the infected population. Absent any intervention, researchers estimate that COVID-19 has a likely R0 between 2 and 4.

The morbidity or prevalence rate of a disease is the total proportion of a population found to be affected by a disease. It is calculated by taking the number of known cases and dividing by the total number of the relevant population. The incidence or infection rate is the rate or likelihood that new cases occur during a given time period. It is calculated by taking the number of new cases and dividing by the total relevant population in a given time frame. It is possible for highly infectious diseases to have a low morbitity rate (such as when individuals quickly recover). It is also possible for medical conditions with relatively low risk to have high prevalence rates (such as when there is no known cure and total cases slowly accumulate over time). Note that these rates are calculated from the number of confirmed positive test case. These numbers may not accurately reflect the "true" rates if cases are not reported or identified.

The proportion of deaths from a given disease compared to the total number of people with the disease. Case Fatality Rate (CFR) is often used as a proxy for a disease's severity, and it reflects the risk over a certain period of time that a person with a given disease will die due to it. Note that it is often difficult to calculate CFR accurately because of cofounding factors (such as other health issues and environmental risks) and because some diseases have long durations. True CFR can only be assessed after all cases have been resolved.

A statistical and economic concept reflecting the fact that there is often a time delay between an event occurring and our ability to detect and report it. This is especially relevant in epidemiology where individuals can be infectious with a particular disease before they show any symptoms or test positive. Factors such as the time it takes to conduct tests and report results, the rate at which testing is conducted, changes in diagnostic criteria, and the natural lifecycle of a disease all contribute to delays before we notice changes. It is crucial to realize that social distancing policies may not produce any noticeable results for 2 or 3 weeks. This is because the number of reported cases is a lagging indicator of the actual situation.

Epidemiological Models

Epidemiological models have been commonplace for many of us right now. They provide a sense of where we are headed and can help us think through difficult mathematical concepts like exponential growth and conditional probability. But it is important to note that they are not infallible oracles, that it is okay for models to disagree with each other, and that we should expect them to change as we encounter new data.

Mathematical epidemiology models usually attempt to simplify complex populations by assigning them to different statuses or compartments and then tracking the flow of people between them. The simplest models use three compartments: S (susceptible), I (infectious), and R (recovered). If we know how many people belong to each compartment, how infectious the disease is, and how frequently people come into contact with each other, we can make an estimate for how people will flow from one compartment to another over time. COVID-19 models tend to be more complicated, both because we need to account for public health interventions and for the possibility of asymptomatic spread. Many models use four compartments or SEIR. These stand for S (susceptible), E (exposed), I (infectious), and R (recovered). The exposed compartment accounts for people who are infected but not actually infectious themselves. When evaluating a model, pay attention to its underlying assumptions and how it handles incomplete or mistaken data.

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Understanding COVID-19 Models & Why They Reach Different Conclusions

Major Models

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MIT Operations Research Center - COVID Analytics


Institute for Health Metrics and Evaluation - COVID-19 Projections


Columbia Mailman School of Public Health - Projected COVID-19 Cases and Hospital Capacity


Los Alamos National Laboratory - COVID-19 Forecasted Case Data

Psychological Wellness

Mental health during times of extraordinary stress and uncertainty is an essential aspect of any pandemic response. Use these resources to find help dealing with anxiety and remaining calm and effective while navigating difficult times.

New Yorkers can call the COVID-19 Emotional Support Hotline at 1-844-863-9314 for free mental health counseling.

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APA Help Center - Ways to manage anxiety, maintain a sense of normalcy, and keep things in perspective during pandemics

Historical Perspective

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JSTOR Daily - Teaching Pandemics

Readings on the history of quarantine, contagious disease, viruses, infections, and epidemics offer important context for the current coronavirus (COVID-19) pandemic.

Digital Public Library of America

DPLA - Images, Text, and Video from across the history of the United States

What "Flatten The Curve" Means

Simple changes in our behavior - regularly and thoroughly washing our hands, disinfecting high contact surfaces, staying six feet apart, and only leaving our home for essential needs - can have widespread effects on the extent and rate at which diseases spread. Even if we did nothing else to fight this pandemic, social distancing and improved personal hygiene will help prevent healthcare systems from being overwhelmed. This is true even if the same total number of people ultimately get sick. By reducing the daily number of cases and spreading out the effects of the pandemic, we can help ensure that as many people as possible will have help when they need it.

Supporting Healthcare Workers & Communities In Need

Doctors, nurses, and emergency personnel are working tirelessly to help protect people during the COVID-19 pandemic. They are doing this despite critical shortages in protective equipment and hospital capacity. The first and most important step you can take to help everyone is to stay home as much as possible. By helping to slow and stop the spread of the virus, you are preventing hospitals from being overwhelmed.

After that step, consider some of the following relief efforts.

Food Bank of the Hudson Valley

Food Bank of the Hudson Valley is the Orange County food bank network hub. With school closures, economic insecurity, and people struggling to stay healthy in grocery stores, ensuring that everyone has enough food is essential. See their emergency responses to COVID-19 here.

NYC Health + Hospitals

New York City Health + Hospitals is the largest public health care system in the nation, serving more than one million New Yorkers annually in more than 70 patient care locations across the five boroughs. Their mission is to care for all regardless of ability to pay or immigration status. During this unprecedented time, NYC Health + Hospitals and all other health care facilities in New York need help to protect and support their staff. This includes things like providing them with protective equipment, food, transportation, and safe lodging while they are too busy working around the clock to care for people sick with COVID-19. Every donation helps.

Center for Disaster Philanthropy

The Center for Disaster Philanthropy is a nonprofit organization working to ensure that people can be informed, intentional, and effective with their charitable giving during times of crisis. They evaluate and partner with local charities in order to direct resources where they are more urgently needed. They identify key areas of need and ensure that all needs that arise during a disaster are met. Their overarching COVID-19 Response Fund is here.

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GoFundMe is a major online crowdsourcing platform for both organizations and individuals to raise money for worthy causes. They have set up a central hub for COVID-19 relief fundraisers here. You can also search for independent fundraisers on the platform. Make sure your donation has the impact you want! Thoroughly research an organization before donating.

Emergency Preparedness

All emergency responses rely on proper planning and preparedness. Take some time, during this current and any future pandemics, to consider if you have an emergency kit and a plan in case a family member gets sick. The best time to consider these things is before they occur, so you can respond calmly and effectively.


ready.gov is a joint project of the Department of Homeland Security and the Federal Emergency Management Agency (FEMA). It provides planning tips and checklists for a wide variety of emergencies, including pandemics. Use their emergency kit checklist to get ideas for the sort of equipment and supplies you might need during an emergency.

Shelter-in-place orders and bans on nonessential travel can be stressful and surreal, especially because, unlike weather-related disasters, the outside world looks normal. Consider these categories of items when preparing to stay at home as much as possible. (Hover over the picture to zoom in.)

How to prepare for staying at home

Stocking your pantry effectively is a straightforward process - and it can help make your home cooking more enjoyable! Consider these tips for food items to get and those to avoid.

Remember that panic buying and hoarding is counterproductive. Rushing out to stores to find a particular item increases the chance of COVID-19 spreading in grocery stores. Try calling ahead to a store to ask if they have what you want and if there is a time when the store is less crowded. Be considerate to your neighbors and community members. If you buy too much, you are making it harder for others to get the supplies that they need.

Online Education Resources

Check out our page for
Kids' Games, Activities, and Education Resources Online!

Time at home is a perfect opportunity for
Adult Online Learning!

Staying Entertained & Busy At Home

As more festivals, performances and concerts are canceled due to the coronavirus shutdown, musicians of all stripes and sizes are taking to social and streaming platforms to play live for their fans.

Billboard maintains a weekly updating list of virtual music festivals and livestreams during the pandemic.

New York City Ballet

New York City Ballet is streaming performances for free for a limited time during the fall season.

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As long as schools are closed, Audible is offering its Stories service for free. Children and adults can enjoy a wide selection of audiobooks, streamable to any device without any setup. Keep you mind active, entertained, and filled with wonder!

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Roll 20 is a free platform for playing tabletop games online. They have partnered with Wizards of the Coast and other roleplaying games makers to bring additional content and adventures to people during this difficult time. This is an excellent way to play games with friends. Social distancing doesn't have to be isolating!