Short answers, pulled from the story.
The COVID-19 pandemic began with an outbreak in Wuhan, China, in December 2019. The WHO was notified of the cluster of unknown pneumonia cases on the 31st of December 2019, and declared the outbreak a public health emergency of international concern on the 30th of January 2020. The WHO formally assessed it as a pandemic on the 11th of March 2020.
COVID-19 is caused by SARS-CoV-2, a positive-sense single-stranded RNA coronavirus closely related to bat and pangolin coronaviruses. The scientific consensus is that the virus most likely originated from a zoonotic source, probably bats or a closely related mammal. Molecular clock analysis suggests the first human cases may have occurred between October and November 2019.
Estimates of total deaths vary widely due to undercounting. The Economist estimated between 18.5 and 35.2 million deaths attributable to the pandemic by the 25th of January 2024. The WHO's own excess mortality analysis found approximately 14.9 million more deaths than expected by the end of 2021, compared with 5.4 million officially reported COVID-19 deaths at that time. COVID-19 was the fifth-deadliest pandemic or epidemic in history.
The United Kingdom became the first developed country to approve the Pfizer vaccine on the 2nd of December 2020, with 800,000 doses immediately available. A June 2022 study estimated COVID-19 vaccines prevented between 14.4 and 19.8 million deaths across 185 countries in just the first year of rollout. By August 2024, more than 5.6 billion people had received at least one dose, with 13.7 billion total doses administered. The Oxford-AstraZeneca vaccine was the most widely used globally.
The WHO designated five major variants of concern: Alpha (UK), Beta (South Africa), Gamma (Brazil), Delta (India), and Omicron (Botswana). Alpha showed changes to the spike protein that increased infectivity. Delta forced the UK to delay reopening in 2021 and raised concerns about transmission among vaccinated people. Omicron, detected on the 24th of November 2021, was more infectious than Delta and drove a surge that pushed Europe past 100 million cases by the 1st of January 2022.
On the 5th of May 2023, the WHO downgraded COVID-19 from a global health emergency, reclassifying it as an established and ongoing health issue. The decision followed the International Health Regulations Emergency Committee's assessment that declining deaths, widespread vaccination, and high population immunity justified removing the emergency designation. The WHO does not make official declarations of when pandemics end, and by 2025, experts generally regarded COVID-19 as having transitioned to the endemic phase.