Health officials in China have published the first details of more 44,000 cases of covid~19 in the biggest study since the outbreak began .Since China first announced the outbreak on December 31, 73,336 cases have been recorded, including 1,875 deaths. While the vast majority of cases and deaths are still occurring in mainland China, Covid-19 has already made its way to at least 25 other countries, including the US, Malaysia, Egypt, and Canada. Markets are on edge. Businesses and cruise ship itineraries have been interrupted. Cities and countries are responding with unprecedented quarantines and travel bans. The whole thing feels a lot like the 2011 pandemic film Contagion.
But to know whether this is really the next deadly pandemic — a disease that spreads globally and could kill millions of people — we need answers to two basic questions: How easily does Covid-19 spread from person to person, and how severe is the virus? At the moment, scientists only have informed guesses, which are likely to solidify in the coming weeks and months. But they’re learning more by the day — and what we know so far is instructive.
The R0, explained
With every disease outbreak, epidemiologists try to figure out how far — and how fast — a virus is likely to spread through a population. To do that, they use the basic reproduction number, called the “R naught,” or R0.
The figure refers to how many other people one sick person is likely to infect on average in a group that’s susceptible to the disease (meaning they don’t already have immunity from a vaccine or from fighting off the disease before).
The R0 is super important in the context of public health because it foretells how big an outbreak will be. The higher the number, the greater likelihood a lot of people will fall sick.
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