Dr. Tomer Altman explains what primers and probes are in the context of PCR tests for detecting pathogens such as SARS-CoV-2 when someone is infected with COVID-19. He explains the issues he found in the original CDC primer and probe designs, as well as his thoughts on what may have caused the issues. He then walks us through how these sequences are designed, giving a very clear tutorial of the bioinformatic design of oligonucleotide sequences for diagnostics use. For more information, please see https://tomeraltman.net/2020/03/03/technical-problems-COVID-primers.html and https://tomeraltman.net/2020/03/11/COVID-19-candidate-primers-update.html