CDC Could & Should Have Backed Up Their Isolation and Quarantine Policy Change with Evidence – A Major Unforced Error
Yesterday the CDC shortened the recommended isolation time for people that test positive for COVID-19 from 10 to 5 days if a person is asymptomatic (followed by 5 days of wearing a mask when around others). In their press statement the CDC wrote that: “... the change is motivated by science demonstrating that the majority of SARS-CoV-2 transmission occurs early in the course of illness, generally in the 1-2 days prior to onset of symptoms and the 2-3 days after“.
CDC also updated the recommended quarantine period for those exposed to COVID-19. For people who are unvaccinated or are more than six months out from their second mRNA dose and not yet boosted, CDC now recommends quarantine for 5 days followed by strict mask use for an additional 5 days
There’s been a lot of push back in the public health and medical communities that believe the CDC’s new guidance counterproductive and not evidence-based… for good reason. While the CDC states in their media-release that their decision is based on “… science demonstrating that the majority of SARS-CoV-2 transmission occurs early in the course of illness, generally in the 1-2 days prior to onset of symptoms and the 2-3 days after” the CDC provided no evidence or even references to back up their statement- a major flaw for any administrator making such a sweeping change to the guidance.
Since the CDC neglected to include a literature review or provide any other evidence other than a statement without references, I went to the literature to see if their statement holds up for them. I found a few studies to support the CDC’s policy change. For example, He X et.al. found that infectiousness peaked between two days before and one day after symptom onset and declined within seven days. Cheng HY et.al. evaluated 2500 close contacts of 100 patients with COVID-19 and found that all of the 22 secondary cases had their first exposure within 6 days of symptom onset. There were no infections documented in the 850 contacts whose exposure was after 6 days of symptom onset. I found some other studies similar results that they could have used to defend their decision (references included at the end).
Editorial Note: Director Walensky made a rookie mistake when she announced this major policy change without providing evidence to support her decision. The CDC is packed with talented epidemiologists that could have easily prepared a Morbidity and Mortality Weekly Report with a complete literature review to support her decision (there are some data to support the policy change). Instead, she chose to make a major policy change without presenting evidence to support the decision. As a result, the CDC lost some street credibility. This was a major unforced error.
- Zou L, Ruan F, Huang M, et al. SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients. N Engl J Med 2020; 382:1177.
- To KK, Tsang OT, Leung WS, et al. Temporal profiles of viral load in posterior oropharyngeal saliva samples and serum antibody responses during infection by SARS-CoV-2: an observational cohort study. Lancet Infect Dis 2020; 20:565.
- He X, Lau EHY, Wu P, et al. Temporal dynamics in viral shedding and transmissibility of COVID-19. Nat Med 2020; 26:672.
- Jones TC, Biele G, Mühlemann B, et al. Estimating infectiousness throughout SARS-CoV-2 infection course. Science 2021; 373.
- Ge Y, Martinez L, Sun S, et al. COVID-19 Transmission Dynamics Among Close Contacts of Index Patients With COVID-19: A Population-Based Cohort Study in Zhejiang Province, China. JAMA Intern Med 2021; 181:1343.