covid 19 questions

COVID 19 questions and answers in an easy-to-understand way, from solid science you can trust.

Filter by KEYWORD:
Thank you! Your submission has been received!
Oops! Something went wrong while submitting the form.

Covid-19 definitions


Antibodies are proteins that the body makes in response to an infection.


COVID-19 is a disease caused by a new strain of coronavirus. COVID is an acronym. ‘CO’ stands for corona, ‘VI’ for virus, ‘D’ for disease, and ‘19’ for 2019 (year first identified). This disease has also been referred to as ‘2019 novel coronavirus’ or ‘2019-nCoV. See World Health Organization for information about COVID-19 in other countries.

COVID-19 Deaths

According to NCDHHS data, “COVID-19 deaths include people who have had a positive molecular (PCR) or antigen test for COVID-19, who died without fully recovering from COVID-19, and who had no alternative cause of death identified. Deaths are reported by hospitals and clinicians directly to the local and state health departments.”

Case fatality ratio

The proportion of people recorded as confirmed COVID-19 cases who die from COVID-19. May be approximated by dividing the number of deaths by the number of confirmed cases. Because many infections are asymptomatic and/or undiagnosed (see “course of illness” FAQ), the case fatality ratio is greater than or equal to the infection fatality ratio.


A group of COVID-19 cases that are linked by the same location or event (e.g., work party, vacation, etc.), outside of a household.


Morbidity means an illness. Illnesses that are happening at the same time in one person are called co-morbidities. For example, someone with diabetes and heart disease has co-morbidities. Some co-morbidities make individuals more likely to have a hard time getting better if they also get COVID-19. Morbidity does not mean death. 

Contact tracing

A public health strategy that helps public health professionals (1) find infected individuals, and (2) find people who were in contact with the infected individual and may have been exposed to the virus.

Cumulative cases

The total number of cases that have been diagnosed up to a certain point in time (data on this dashboard started on June 2, 2020 unless noted otherwise).

Herd Immunity

Immunity that occurs through the presence of immune persons (people who have been vaccinated or previously infected) in the surrounding population. When the percentage of immune persons is high enough (the “herd immunity threshold”), which varies from infection to infection, the likelihood of infection among the entire population decreases.

Infection fatality ratio

The proportion of people infected with SARS-CoV-2 who die from COVID-19. If the number of infections is known, this measure may be approximated by dividing the number of deaths by the number of infections. Because many infections go undetected, the infection fatality ratio is lower than the case fatality ratio.

Maximum allowable dilution (MAD)

The maximum level of dilution of assay sensitivity that the user will allow, and is typically determined a priori.


Another word for death. COVID-19 mortality refers to deaths where SARS-CoV-2 infection was a contributing cause. According to the Centers for Disease Control and Prevention (CDC), COVID-19 should not be reported on the death certificate if it did not cause or contribute to the death.

Number needed to test

A person who is infected with SARS-CoV-2 and has not yet shown symptoms, but later does show symptoms and tests positive for the disease.


The total number of active cases in a population within a specific timeframe. This number is useful because it tells you about the number of people currently infected.

R0 (“R-naught”)

The basic reproduction ratio or basic reproductive number. It is used to describe how many people someone with an infection is expected (on average) to infect in an entirely susceptible population. An outbreak is expected to take hold if R0 has a value >1 and to fade out if R0 is <1.


The virus that causes a respiratory disease called coronavirus disease 19 (see definition COVID-19). SARS-CoV-2 is part of a larger family of viruses called coronaviruses, including SARS-CoV, which led to an epidemic that affected 26 countries and resulted in more than 8000 cases in 2003.

Symptom onset

The time when symptoms start. This is typically 2-14 days after exposure to SARS-CoV-2. Symptoms may include fever or chills, cough, shortness of breath or difficulty breathing, fatigue, muscle or body aches, headache, new loss of taste or smell, sore throat, congestion or runny nose, nausea or vomiting, or diarrhea (from CDC).

Target Population

The group of all individuals who may be eligible for SARS-CoV-2 (COVID-19) testing under a specific testing strategy.

Test sensitivity

The probability that a truly positive individual is correctly classified as positive by that test. (Will be between 0 and 1)

Test specificity

The probability that a truly negative individual is correctly classified as negative by that test. (Will be between 0 and 1)

Upper/Lower Confidence Limit

The highest and lowest numbers in a confidence interval. A confidence interval describes the precision of a result and is provided by most published studies.