The U.S. Response to COVID-19 as of February 24, 2020

A historical report: it describes what CDC knew and was doing as of February 24, 2020, and was posted as an MMWR Early Release on February 25, 2020. CDC's current guidance is at cdc.gov/coronavirus.

At a glance

• An outbreak of coronavirus disease 2019 (COVID-19), caused by the new coronavirus SARS-CoV-2, began in Wuhan, Hubei Province, China, in December 2019. It had spread throughout China and to 31 other countries and territories, including the United States.
• As of February 23, 2020: 76,936 reported cases in mainland China, 1,875 outside it, and 2,462 deaths worldwide — none in the United States.
• The United States had 53 cases: 14 diagnosed in the country, plus 39 among repatriated people from high-risk settings.

The aim: slow it down

CDC, state and local health departments, other federal agencies and partners were taking aggressive measures to slow and try to contain the virus. These depended on finding cases and their contacts, and on assessing, monitoring and caring for travelers from areas with substantial transmission.

The report said plainly that these steps might not prevent widespread transmission. They were meant to:

1. Slow the spread of illness.
2. Give time to health departments, health systems, businesses, schools and the public to prepare in case widespread transmission came.
3. Learn more about COVID-19, to guide recommendations and the development of diagnostics, treatments and vaccines.

CDC was coordinating with the World Health Organization (WHO) and other global partners.

What was known about the virus

• It appeared to spread from person to person mainly by respiratory transmission; how easily was still unclear.
• Signs and symptoms: fever, cough and shortness of breath.
• CDC estimated that symptoms appear 2–14 days after exposure, based on the incubation periods of the Middle East respiratory syndrome (MERS) and severe acute respiratory syndrome (SARS) coronaviruses and on reports of travel-related cases.
• Early data suggested that older adults and people with underlying health conditions or compromised immune systems might be at greater risk of severe illness.

U.S. cases

As of February 23, 14 cases had been diagnosed in six states:

• Twelve were related to travel to China; 2 came from person-to-person spread to close household contacts of a confirmed patient.
• Another 39 cases were among repatriated U.S. citizens, residents and their families: 3 from Hubei Province and 36 from the Diamond Princess cruise ship, docked at Yokohama, Japan.

CDC's response

Staff. As of February 24, 1,336 CDC staff members had worked on the response, from clinicians and epidemiologists to laboratorians and modelers. 497 (37%) had been deployed to 39 locations in the United States and abroad: quarantine stations at ports of entry, health departments, hospitals, military bases housing quarantined people, WHO and ministries of health. They helped find cases, trace contacts, evaluate persons under investigation (PUIs) and manage patients,, and worked with academic partners to study the virus.

Other agencies. With the Department of Homeland Security, CDC screened travelers at the 11 airports to which all flights from China were being directed, and referred them to health departments for self-monitoring. With the Departments of Defense, Health and Human Services, and State, it helped evacuate U.S. citizens, residents and their families from places with substantial, sustained transmission, then house them and monitor their health through a 14-day quarantine.

Guidance. CDC posted guidance for health care settings and international travel and, to prepare for community spread, tailored materials for communities, public health, laboratories, schools and businesses, some in Chinese and Spanish.

Travel notices

CDC also posted information on apparent community transmission in Singapore, Taiwan, Thailand and Vietnam, and advised people to reconsider cruise ship voyages in Asia.

Airport screening

• 46,016 air travelers had been screened at the 11 airports as of February 23.
• Since February 2, entry for anyone who had been in China in the previous 14 days was limited to U.S. citizens, lawful permanent residents and others named in a presidential proclamation.
• Passengers were screened for fever, cough and shortness of breath; anyone with signs of illness received a fuller assessment.
• 11 travelers were sent to a hospital and tested; 1 tested positive and was isolated and treated.
• 17 were quarantined for 14 days after travel from Hubei Province, designated high-risk; 13 had finished quarantine.

Testing people under investigation

As of February 23, 479 people from 43 states and territories had been or were being tested:

Laboratory work

• From January 18 to February 23, CDC laboratories used real-time RT-PCR to test 2,620 specimens from 1,007 people. Selected state and other public health laboratories also tested, with confirmation at CDC.
• CDC was developing a serologic test, detecting antibodies (IgG, IgA and IgM) that show exposure or past infection, to help track the virus's circulation in the U.S. population, and tests for the virus's RNA and antigens in tissue specimens.
• After growing SARS-CoV-2 in cell culture, CDC shared isolates with the Biodefense and Emerging Infections Research Resources Repository, which distributes them securely to U.S. public health and academic institutions for research, including vaccine development.

Repatriation flights

From Hubei. Between January 29 and February 6, 808 U.S. citizens, residents and family members came home on five chartered flights, all free of symptoms when they left. They were quarantined for 14 days at five military bases. 28 (3%) developed symptoms and were evaluated; 3 tested positive and were referred for medical care and isolation. By February 24, the other 805 had completed quarantine.

From the Diamond Princess. On February 3, the ship's passengers and crew were quarantined off Yokohama after a passenger who had recently left the ship in Hong Kong was confirmed to have COVID-19, and transmission continued on board. By February 16, 355 cases had been identified among passengers and crew, 67 of them U.S. citizens or residents. On February 16–17, the U.S. government helped bring 329 U.S. citizens and residents home on two chartered flights. As of February 23, 36 (11%) had tested positive and were under medical supervision; the rest were in 14-day quarantine.

What CDC expected next

COVID-19 was not yet recognized as spreading in U.S. communities. If sustained community transmission were found, the response would step up actions to slow spread in communities, and basic precautions — staying home when ill and respiratory and hand hygiene — would become increasingly important.

Community measures might include school dismissals and social distancing elsewhere: postponing or canceling mass gatherings, and telework and remote meetings at workplaces. These can be disruptive and costly, but studies had shown that early, layered measures can reduce community spread of pathogens such as pandemic influenza, even without drugs or vaccines. China's measures — closing major transport hubs, stopping people leaving some cities, canceling Chinese New Year celebrations and barring attendance at school and work — had not yet been evaluated.

Treatments and vaccines. The National Institutes of Health (NIH) and collaborators were developing candidate vaccines and treatments. China had several clinical trials of investigational drugs, two of them of the antiviral remdesivir. An NIH randomized controlled trial of investigational treatments for hospitalized U.S. patients, approved by the Food and Drug Administration, would study remdesivir first. Without a vaccine or specific treatment, community mitigation was the main response to widespread transmission, and supportive care the treatment.

Flu season. COVID-19's symptoms resemble influenza's, and the outbreak came when flu and other respiratory viruses, including the coronaviruses behind the common cold, were widespread. To prevent flu, and unnecessary evaluation for COVID-19, everyone aged 6 months and older should get an annual flu vaccine — still available and effective. People with symptoms who had contact with a case or recent travel to countries with apparent community spread should call their health care provider before seeking care.

Open questions

1. The incubation period and how long the virus is shed — which set how long quarantine should last.
2. How much each route of spread — droplets, aerosols and fomites — matters, which shapes infection control and protective equipment.
3. The severity and case-fatality rate among U.S. patients, and the risk factors for infection and severe disease.
4. The role of asymptomatic infection in ongoing transmission.
5. The immune response to infection, to help develop vaccines and treatments.

Sources

Based on Jernigan DB; CDC COVID-19 Response Team, "Update: Public Health Response to the Coronavirus Disease 2019 Outbreak — United States, February 24, 2020," MMWR Morbidity and Mortality Weekly Report, volume 69, Centers for Disease Control and Prevention, posted February 25, 2020; a work of the United States government in the public domain. The source's misspelling "COVD-19" is corrected.