The collection of data that the United States and many other countries had come to rely on to understand the threat posed by emerging variant and the effectiveness of vaccines has been disrupted by the British government. In the last few months, Denmark has cut back on its virus tracking efforts.

As more countries loosen their policies toward living with Covid rather than snuffing it out, health experts worry that monitoring systems will become weaker, making it more difficult to predict new surge and to make sense of emerging variant.

The Rockefeller Foundation's Pandemic Prevention Institute's managing director said things are going to get harder.

Since the Alpha variant emerged in the fall of 2020, Britain has served as a bellwether, tracking that variant as well as Delta and Omicron before they arrived in the United States. After a slow start, Americangenomicssurveillance efforts have steadily improved with a modest increase in funding.

The US might be in a leadership position as a result of this.

Britain was prepared to set up a world-class virus tracking program. The country had large labs ready to sequence viral genes, and it could link that to electronic records from its National Health Service, which was already home to many experts on virus evolution.

British researchers created a consortium in March of 2020 to sequence as many viral genomes as possible. Some came from tests people took when they felt unwell, others came from hospitals, and still others came from national surveys.

Experts said that the last category was important. By testing hundreds of thousands of people at random each month, the researchers were able to detect new variant and outbreak among people who didn't know they were sick, rather than waiting for tests to come from clinics or hospitals.

The community testing has been the most rapid indicator of changes to the epidemic, and it has also been the most rapid indicator of the appearance of new variant.

A train car converted into a Covid testing site in Brighton.
ImageA train car converted into a Covid testing site in Brighton.
A train car converted into a Covid testing site in Brighton.Credit...Chris Eades/Getty Images

By late 2020, Britain was providing online databases with more than half of the world's coronaviruses genomes. This data allowed researchers to identify Alpha, the first variant of the coronaviruses, in an outbreak in southeastern England.

The countries that stood out for their efforts to track the evolution of the virus were a few. Most of the positive coronaviruses tests in Danes were done with an ambitious system. Israel's combination of viral tracking and aggressive vaccinations produced evidence last summer that the vaccines were becoming less effective, data that other countries leaned on in their decision to approve boosters.

Combining the information from the genomes with medical records and epidemiology made sense of the variant.

The U.K. set itself up to give information to the whole world, according to the former director of the Covid-19 Genomics Initiative.

In the past few weeks, Britain's surveillance systems gave the world crucial information about the BA.2 subvariant of Omicron. The variant does not pose a greater risk of hospitalization than other forms of Omicron, according to British researchers.

Two of the country's routine virus surveys were shut down and a third was scaled back, baffling Dr. Fraser and many other researchers. The government stopped paying for free tests, as well as canceled or paused sewage sampling programs.

I don't know what the strategy is to put together these large instruments and then dismantle them.

Prime Minister Boris Johnson has called for Britain to learn to live with the disease, and the government pointed to the success of the country's vaccine program. The government will continue to monitor cases in hospital settings, including usinggenomics, which will allow some insights into the evolution of the virus.

Life with Covid is different now than it was in the spring of 2020. In countries that have enough people to receive a vaccine, the risk of hospitalization and death is greatly reduced. Antiviral pills are still in short supply in much of the world, but they can further blunt Covid's devastation.

After two years, it made sense for countries to look for ways to curb spending.

Genomic sequencing of Covid samples at the Wellcome Sanger Institute in Cambridgeshire, England.
ImageGenomic sequencing of Covid samples at the Wellcome Sanger Institute in Cambridgeshire, England.
Genomic sequencing of Covid samples at the Wellcome Sanger Institute in Cambridgeshire, England.Credit...Frank Augstein/Associated Press

He was worried that cutting back too much would leave Britain unprepared for a new variant.

Steven Paterson, a geneticist at the University ofLiverpool, pointed out that Britain will have fewer viruses to sequence with a reduction in testing. He thought the output could go down by 80 percent.

It will lead to a degradation of the insight that we can have into the number of infections, or the ability to spot new ones as they come through.

When a new variant of the coronaviruses emerges, it will be difficult to restart the programs that were halted.

If there is one thing we know about the disease, it is that it always surprises us.

The live-with-covid philosophy is being applied by other countries. The testing rate has dropped from its January peak. The tests would only be required for certain medical reasons.

The country was trying to convince itself that the epidemic was over, according to an Oxford virologist.

She said that the daily case count in Danes doesn't reflect the true state of the Pandemic because of the drop in testing. The country is ramping up widespread testing of wastewater, which may be able to detect new variations. The country could start testing again if the wastewater showed a spike.

She said she was confident that the country would be able to scale up.

The director of the Clalit Research Institute in Israel said that the country's health care systems will continue to track the effectiveness of vaccines.

A volunteer in Woking, England, collected a completed Covid home testing kit.
ImageA volunteer in Woking, England, collected a completed Covid home testing kit.
A volunteer in Woking, England, collected a completed Covid home testing kit.Credit...Matt Dunham/Associated Press

South Africa has a model of robust-yet-affordable virus monitoring that is very similar to Britain's.

Researchers discovered Omicron in South Africa in November. The country only has a few hundred virus genomes a week.

The design of the survey was credited by the director of South Africa's Centre for Epidemic Response and Innovation. He and his colleagues randomly pick out test results from all over the country. That method makes sure that a bias in the survey doesn't lead them to miss something important.

They run leaner operations than richer countries. The survey has cost less than $2 million since it started.

In contrast, many countries in Africa and Asia have yet to start any large-scale research.

The United States has traveled on its own. When the Alpha variant swept across the country, American researchers were only able to sequence a tiny fraction of positive Covid tests.

State and local public health departments have been helped by the Centers for Disease Control and Prevention to sequence their own viruses. The United States is still ramping up its efforts even though other countries are pulling back. The C.D.C. announced an initiative last month.

The country's long-term surveillance is uncertain because of budget fights in Washington. The United States faces obstacles that other wealthy countries don't.

Without a national health care system, the country cannot link each virus sample with a person's medical records. The United Kingdom and South Africa have had a regularly updated national survey set up by the United States.

If we had something like that, scientists would love it.