The healthcare community's understanding of COVID-19 has greatly evolved since the novel virus first reached the U.S. in January, prompting many CDC updates, walk-backs and suspicions of political influence along the way.
Here are 16 of the most significant CDC pandemic response actions since February:
16. Dec. 4
CDC update calls for universal mask-wearing
Why it's notable: The agency called for universal mask use at all times indoors, except inside one's own household, and outside when distances of 6 feet or more cannot be maintained — the first time the CDC has called for indoor universal mask wearing.
15. Dec. 2
CDC cuts COVID-19 quarantine recommendation
Why it's notable: In an effort to get more people to comply, the CDC trimmed the previous 14-day quarantine guideline for people who are exposed to 10 days without symptoms, or seven with a negative test.
14. Dec. 1
CDC panel recommends healthcare workers, nursing home residents get COVID-19 vaccine first
Why it's notable: CDC director Robert Redfield, MD, has since accepted the vaccine priority recommendation.
13. Nov. 20
CDC warns against Thanksgiving travel
Why it's notable: The warning ahead of the holiday season came during the same week the U.S. saw one million new COVID-19 cases.
12. Nov. 10
CDC takes stronger stance on masks
Why it's notable: This update marked the first official acknowledgement that masks protect wearers, not just those around them.
11. Oct. 22
The CDC revised its definition of 'close contact' with someone who has COVID-19
Why it's notable: Previously, the agency defined "close contact" as 15 minutes of continuous exposure, while the current definition includes a total of 15 minutes of exposure spent six feet or closer to an infected individual. For more on what counts as "close contact", click here.
10. Oct. 5
CDC clarifies stance on airborne COVID-19 transmission after previous mix-up
Why it's notable: In some cases, people farther than six feet apart can become infected by tiny aerosols, the CDC clarified after retracting an earlier update saying the virus can spread via airborne transmission. The earlier update was an unreviewed draft version that mistakenly said airborne spread is the primary driver of transmission, the CDC said.
9. August 26
CDC waives testing recommendation for people without symptoms
Why it's notable: This update said people exposed to coronavirus don't need a test if they don't have symptoms, stirring up confusion among the healthcare community given the prevalence of asymptomatic infection. Prior to this, the agency recommended all in close contact be tested. The CDC has since reinstated the original recommendation that anyone with close contact be tested.
8. July 27
CDC vows to address COVID-19 disparities, health equity
Why it's notable: COVID-19 spotlighted long existing health disparities in the U.S., and this was the CDC's first comprehensive acknowledgement of that. In a strategy document, the CDC pledged to develop disease management practices, such as improved data collection and increased access to testing, in an effort to improve health outcomes among disproportionately affected populations, including racial and ethnic minorities.
7. May 20
COVID-19 does not easily spread via contaminated surfaces, CDC says
Why it's notable: This declaration reiterated that respiratory droplets are the primary mode of transmission, underscoring the importance of masks and social distancing as prevention measures.
6. April 27
CDC added 6 new potential symptoms to its initial three
Why it's notable: Originally only listing fever, cough and shortness of breath as virus symptoms, the agency added chills, repeated shaking with chills, muscle pain, headache, sore throat and new loss of taste or smell.
5. April 15
Screen every hospital visitor for fever, symptoms, CDC says
Why it's notable: This update recommends that everyone entering a hospital wear a mask and for hospitals to forego contact tracing efforts in favor of pre-entry screenings.
4. April 9
CDC deletes advice on front-running COVID-19 drugs from website
Why it's notable: In March, the CDC posted guidance saying antimalarial drugs hydroxychloroquine and chloroquine were "well tolerated" and recommended for hospitalized COVID-19 patients in other countries. This update pulled back on the guidance, simply noting the drugs are under investigation in clinical trials. The FDA has since cautioned against the use of the drugs due to reports of heart complications.
3. April 2
Up to 25% of coronavirus patients may not show symptoms, CDC director says
Why it's notable: This marks the first estimate of how many cases are asymptomatic — that number has since jumped to 40 percent.
2. March 9
Healthcare workers exposed to coronavirus get new CDC guidelines
Why it's notable: As community spread grew in the U.S., resource consuming strategies like formal contact tracing may not be practical in every circumstance for healthcare workers, the CDC said. This was the first time the CDC rolled back on guidelines, instead recommending a universal symptom screening process and allowing those with low-risk exposures to continue working.
1. February 14
The new coronavirus can be spread by people who don't show symptoms
Why it's notable: This was the first time the CDC warned of asymptomatic COVID-19 spread, heightening concerns of rapid transmission in the U.S.
More articles on public health:
Number of COVID-19 hospitalizations, state by state: Dec. 14
Pfizer vaccine nears emergency approval; daily COVID-19 deaths may surpass 9/11 toll for months, Redfield says — 5 updates
23 states where COVID-19 is spreading fastest, slowest: Dec. 14