How an outbreak became a pandemic: a chronological analysis of crucial junctures and international obligations in the early months of the COVID-19 pandemic

Lancet. 2021 Dec 4;398(10316):2109-2124. doi: 10.1016/S0140-6736(21)01897-3. Epub 2021 Nov 8.


Understanding the spread of SARS-CoV-2, how and when evidence emerged, and the timing of local, national, regional, and global responses is essential to establish how an outbreak became a pandemic and to prepare for future health threats. With that aim, the Independent Panel for Pandemic Preparedness and Response has developed a chronology of events, actions, and recommendations, from December, 2019, when the first cases of COVID-19 were identified in China, to the end of March, 2020, by which time the outbreak had spread extensively worldwide and had been characterised as a pandemic. Datapoints are based on two literature reviews, WHO documents and correspondence, submissions to the Panel, and an expert verification process. The retrospective analysis of the chronology shows a dedicated initial response by WHO and some national governments, but also aspects of the response that could have been quicker, including outbreak notifications under the International Health Regulations (IHR), presumption and confirmation of human-to-human transmission of SARS-CoV-2, declaration of a Public Health Emergency of International Concern, and, most importantly, the public health response of many national governments. The chronology also shows that some countries, largely those with previous experience with similar outbreaks, reacted quickly, even ahead of WHO alerts, and were more successful in initially containing the virus. Mapping actions against IHR obligations, the chronology shows where efficiency and accountability could be improved at local, national, and international levels to more quickly alert and contain health threats in the future. In particular, these improvements include necessary reforms to international law and governance for pandemic preparedness and response, including the IHR and a potential framework convention on pandemic preparedness and response.

Publication types

  • Systematic Review

MeSH terms

  • Animals
  • COVID-19 / epidemiology*
  • COVID-19 / transmission
  • China / epidemiology
  • Disease Outbreaks
  • Global Health / legislation & jurisprudence
  • Humans
  • Information Dissemination
  • International Cooperation
  • International Health Regulations
  • Pandemics*
  • Risk Assessment
  • SARS-CoV-2 / isolation & purification
  • Time Factors
  • World Health Organization
  • Zoonoses / virology