COVID questions: Economic recovery, different tests
Editor’s note: We will be publishing answers to questions about COVID-19 and the pandemic each week in this COVID questions column. If you have a question, please email it to covid19update@uc.wisc.edu.
Q: What is the difference between a PCR test and an antigen test?
A: Tests for SARS-CoV-2, the virus that causes COVID-19, have two main parts. First there is the kind of sample taken to look for the virus. This could be a nasal swab, the infamous nasopharyngeal swab (the deep nasal swab sometimes jokingly called a brain swab), or a sample of saliva. Any of these sample types could be used with any of the following test types, though in practice each test type has one or more preferred sample types.
PCR tests look for the virus’s genetic material. PCR is an extremely sensitive technique — it can detect very small amounts of genetic material in a swab or saliva sample. In most people, it seems that contagiousness begins a day or two before the onset of symptoms and ends after symptoms resolve. But in most infected people there seems to be a period of time after symptoms end in which there is a small amount of virus remaining. This small amount can be detected by very sensitive PCR tests, but it is not enough to transmit to another person. That is, after symptoms resolve, you might be positive by PCR, but not contagious. (For this reason, it would be helpful if PCR test results reported the amount of virus detected, and not just “positive” or “negative.” Then doctors could have a better sense of whether someone might be contagious to others.)
This is where antigen tests come in. They can use the same sorts of samples that PCR tests do, but instead of looking for genetic material, they look for pieces of the virus itself, called antigens. Antigen tests are rapid — they can give results in just minutes. Right now, it seems like antigen tests are almost as good as PCR at detecting SARS-CoV-2 — IF the person being tested has symptoms and has had them for a week or less. The data on this is not as solid, but antigen tests seem to be less reliable in people who do not have symptoms. We need more studies to know whether antigen tests will be a good tool for screening people without symptoms.
In any question about testing, I feel it’s important to add that we all need to keep up our other prevention strategies, like distancing and masking, whether we get tested or not. A negative test today does not mean that you will be negative tomorrow. It’s particularly important to remember this as we want to gather with friends and family for the holidays. We should not view a negative test on, say, Friday as a license to gather without precautions on Saturday or Sunday.
– Thomas Friedrich, Professor, Pathobiological Sciences; Virology Services unit head, Wisconsin National Primate Research Center
Q: Has the announcement of a COVID-19 vaccine had any impact on the outlook of economic recovery?
A: Yes, I think it has had a positive impact. Much of the impact of COVID has not come from government order shutdowns, but rather consumers not feeling comfortable going out and spending money. While my wife and I do carryout from local restaurants to help them out, we will NOT eat in the restaurant because of fears of the pandemic. The majority of folks fall into that category. Until we feel safe, we will hunker down. With the vaccines rolling out, we can now see that we can return to restaurants, the movies, etc., in the not too distant future.
Another way to think about it is consumer confidence: with the pandemic consumer confidence has dropped like a rock, people will not spend because we are unsure about what the future holds or we have a poor outlook. With the announcement of the vaccines, people’s confidence will start to rise. But until we see significant and sustained drops in infection rates, people may feel better about the future of the economy, but will remain in the hunker down. There is some research that suggests it’s not the infection rate that people are reacting to, but rather the death rates.
– Steven Deller, Professor and Community Development Specialist, Agricultural and Applied Economics
See more answers to COVID questions at https://news.wisc.edu/tag/covid-questions/. Also, visit our COVID-19 impact site.
