From Wikipedia,

A lockdown is a restriction policy for people or community to stay where they are, usually due to specific risks to themselves or to others if they can move and interact freely. The term "stay-at-home" or "shelter-in-place" is often used for lockdowns that affect an area, rather than specific locations. [...]

During the COVID-19 pandemic, the term lockdown was used for actions related to mass quarantines or stay-at-home orders. The first lockdown during the pandemic was implemented in Wuhan on January 23, 2020. By early April 2020, 3.9 billion people worldwide were under some form of lockdown—more than half the world's population. By late April, around 300 million people were under lockdown in nations of Europe, while around 200 million people were under lockdown in Latin America. Nearly 300 million people, or about 90 per cent of the population, were under some form of lockdown in the United States, and 1.3 billion people have been under lockdown in India.

The COVID-19 lockdowns were unique in global history. Before, quarantines were more localized, and stay-at-home orders were rare, owing to the fact that most people could not work from home. The rise of internet work has enabled stay-at-home orders.

Natural viral spillover events are common and may be becoming more common as the human population rises. Furthermore, the stupendous fall of deaths from infectious disease has arguably lowered humanity's threshold for the type of infectious event considered worthy of lockdown as a means of prevention.

During the mid 21st century, it may become possible for small groups to artificially engineer viruses using new techniques like CRISPR/Cas9. Deepmind's recent open-sourcing of AlphaFold 2 and its predictions is expected to greatly enhance our understanding of biology, which may ultimately end up being used for detrimental purposes. This question asks about a secondary effect from viruses in the 21st century: will we keep going on lockdown?