Countries straining to contain a second wave of Covid-19 are turning to faster, cheaper but less accurate tests to avoid the delays and shortages that have plagued efforts to diagnose and trace those infected quickly.
Germany, where infections jumped by 4,122 on Tuesday to 329,453 total, has secured 9 million so-called antigen tests per month that can deliver a result in minutes and cost about 5 euros ($5.90) each. That would, in theory, cover more than 10% of the population.
The United States and Canada are also buying millions of tests, as is Italy, whose recent tender for 5 million tests attracted offers from 35 companies.
Germany's Robert Koch Institute (RKI) now recommends antigen tests to complement existing molecular PCR tests, which have become the standard for assessing active infections but which have also suffered shortages as the pandemic overwhelmed laboratories and outstripped manufacturers' production capacity.
PCR tests detect genetic material in the virus while antigen tests detect proteins on the virus's surface, though both are meant to pick up active infections. Another type of test, for antibodies the body produces in response to an infection, can help tell if somebody has had Covid-19 in the past.
Like PCR (polymerase chain reaction) tests, antigen tests require an uncomfortable nasal swab. They can also produce more "false negatives", prompting some experts to recommend they only be used in a pinch.
Still, the alarming rise in new infections globally has health officials desperately pursuing more options as the winter influenza season looms.
The World Health Organization reported more than 2 million new cases last week, bringing the total worldwide to 37 million, with more than 1 million deaths from Covid-19.
"These point-of-care tests could make a big difference," said Gerard Krause, epidemiology department director at Germany's Helmholtz Centre for Infection Research.
NO TEST NO FLIGHT
Krause said low-priority patients - those without symptoms - could initially be screened with antigen tests, leaving the more accurate PCR tests for those showing signs of the disease.
Antigen tests have already gained traction in the travel industry. Italian airline Alitalia offers Rome-Milan flights exclusively for passengers with negative tests and Germany's Lufthansa has announced similar testing plans.
But pandemic's vast scale has strained the ability of countries to test all of their citizens, making it difficult to track the twisting paths of infection comprehensively and prevent a resurgence.
In the United States, for example, reliance on automated PCR machinery over the summer left many patients frustrated as they waited for a week or more for results.
Testing in Europe has also suffered glitches.
France does over a million tests a week but its free-for-all testing policy has led to long queues and delays in results, prompting French researchers to come up with a test they say can produce results in 40 minutes, without using a swab.
Italy does between 800,000 and 840,000 tests a week, more than double April's levels, according to the Ministry of Health. But a government adviser, University of Padua microbiology professor Andrea Crisanti, said the country needs 2 million tests a week to really get on top of the virus.
In the Netherlands, where infection rates are among Europe's highest, the government has been scrambling to expand weekly testing and lab capacity to 385,000 by next week from 280,000 now. The target is nearly half a million tests a week by December and just under 600,000 by February.
But people have been waiting days for a test. The authorities blame the overwhelming demand from those without clear symptoms for clogging up the system.
In response, the authorities have restricted rapid antigen tests to health workers and teachers, while others go on a waiting list.
The various hitches highlight a conundrum for governments: how to get people back to work while tracing the virus within the population quickly - without running out of supplies.
Swiss diagnostics maker Roche, announced plans on Tuesday to launch a new antigen test by the end of the year that can be processed on lab machines at up to 300 tests per hour, not counting collection time.
Rivals including Siemens Healthineers, Abbott Laboratories and Becton Dickinson also offer numerous Covid-19 diagnostic tests.
Roche said the test could be deployed in places such as nursing homes or hospitals, where speedy results could thwart a potentially lethal outbreak.
By early 2021, the Basel-based company said it could make some 50 million of the new tests a month, on top of the rapid point-of-care tests it already sells.
"The primary use case is the testing of symptomatic patients," a Roche spokeswoman said. "The secondary use case is the testing of individuals suspected of infection ... which could also include asymptomatic patients."
Expert opinion, however, on just how to use antigen tests is evolving and remains the subject of debate.
Switzerland, where new infections have spiked to about 1,500 a day from as low as three in June after schools reopened, is only now validating the accuracy of the rapid tests.
"Deployment of the rapid tests - where it makes sense - will be integrated into our testing strategy," a spokesman for the Swiss federal health ministry said. "We'll update our testing recommendations in November."
Sandra Ciesek, director of the Institute of Medical Virology at the University Clinic in Frankfurt, Germany said rapid antigen tests could be an option for asymptomatic patients planning to visit elderly patients at nursing homes.
But people should refrain from using them as a definitive substitute to judge their infection status.
"The PCR test remains the gold standard," Ciesek said. "An antigen test should only be used as an alternative if PCR is not possible in a timely manner."