Suddenly, the era of big government is back. But is it back 'for good'?

In just a few weeks, a virus a ten-thousandth of a millimeter in diameter has transformed Western democracies. States have shut down businesses and sealed people indoors. They have promised trillions of dollars to keep the economy on life support. If South Korea and Singapore are a guide, medical and electronic privacy are about to be cast aside.

It is the most dramatic extension of state power since World War II.

One taboo after another has been broken. Not just in the threat of fines or prison for ordinary people doing ordinary things, but also in the size and scope of the government's role in the economy.

In America, Congress has agreed to a relief package worth some $2.2 trillion, 10% of GDP, twice what was promised in 2007-09. Credit guarantees by Britain, France and other countries are worth 15% of GDP. Central banks are printing money and using it to buy assets they used to spurn. For a while, at least, governments are seeking to ban bankruptcy.

For believers in limited government and open markets, COVID-19 poses a problem. The state must act decisively. But history suggests that after crises the state does not give up all the ground it has taken. Today that has implications not just for the economy, but also for the surveillance of individuals.

It is no accident that the state grows during crises. Governments might have stumbled in the pandemic, but they alone can coerce and mobilize vast resources rapidly. Today they are needed to enforce business closures and isolation to stop the virus. Only they can help offset the resulting economic collapse. In America and the euro area GDP could drop by 5 to 10% year-on-year, perhaps more.

One reason the state's role has changed so rapidly is that COVID-19 spreads like wildfire. In less than four months, it has gone from a market in Wuhan to almost every country in the world. People are scared of the example of Italy, where recorded cases have overwhelmed a world-class health system, leading to more than 7,500 deaths.

In most of the world the state has so far responded to COVID-19 with a mix of coercion and economic heft. As the pandemic proceeds, it is also likely to exploit its unique power to monitor people using their data. Hong Kong uses apps on phones that show where you are in order to enforce quarantines. China has a passporting system to record who is safe to be out. Phone data help modelers predict the spread of the disease. And if a government suppresses COVID-19, as China has, it will need to prevent a second wave among the many who are still susceptible, by pouncing on every new cluster. South Korea says that automatically tracing the contacts of fresh infections, using mobile technology, gets results in 10 minutes instead of 24 hours.

This vast increase in state power has taken place with almost no time for debate. Some will reassure themselves that it is just temporary and that it will leave almost no mark, as with Spanish flu a century ago. However, the scale of the response makes COVID-19 more like a war or the Depression. And here the record suggests that crises lead to a permanently bigger state with many more powers and responsibilities and the taxes to pay for them. The welfare state, income tax, nationalization, all grew out of conflict and crisis.

As that list suggests, some of today's changes will be desirable. It would be good if governments were better prepared for the next pandemic; so, too, if they invested in public health, including in America, where reform is badly needed. Some countries need decent sick pay.

Other changes may be less clear-cut, but will be hard to undo because they were backed by powerful constituencies even before the pandemic. One example is the further unpicking of the eurozone pact that is supposed to impose discipline on the member-states' borrowing. Likewise, Britain has taken its railways under state control — a step that is supposed to be temporary but which may never be retracted.

More worrying is the spread of bad habits. Governments may retreat into autarky. Some fear running out of the ingredients for medicines, many of which are made in China. Russia has imposed a temporary ban on exporting grain. Industrialists and politicians have lost trust in supply chains. It is but a small step from there to long-term state support for the national champions that will have just been bailed out by taxpayers. Trade's prospects are already dim; all this would further cloud them — and the recovery. And in the long term, a vast and lasting expansion of the state together with dramatically higher public debt is likely to lead to a lumbering, less dynamic kind of capitalism.

The most worrying is the dissemination of intrusive surveillance. Invasive data collection and processing will spread because it offers a real edge in managing the disease. But they also require the state to have routine access to citizens' medical and electronic records. The temptation will be to use surveillance after the pandemic, much as anti-terror legislation was extended after 9/11. This might start with tracing tuberculosis cases or drug dealers. Nobody knows where it would end, especially if, having dealt with COVID-19, surveillance-mad China is seen as a model.

Surveillance may well be needed to cope with COVID-19. Rules with sunset clauses and scrutiny built in can help stop it at that. But the main defense against the overmighty state, in tech and the economy, will be citizens themselves. They must remember that a pandemic government is not fit for everyday life.