They're the tip of the testing spear in the fight against the coronavirus.
It's a fancy word for the main ingredients of any chemical-based test, which in this pandemic includes inorganic solutions as well as enzymes, probes, and primers created to match the coronavirus's genome.
And they are a necessity for the coronavirus test kits that are vital to combating COVID-19, the pneumonia-like disease that by April 18 had killed more than 156,000 of its 2.2 million confirmed sufferers since the coronavirus jumped to humans in central China in November.
The importance of reagents will continue to outstrip supplies in many places as the race for safe and effective vaccines and treatment continue and governments embrace "testing, testing, testing" while they try to lead billions of people out of the great lockdown.
But for all their durability in a vial, the COVID-19 crisis has underscored our vulnerability to reagent shortages brought on by sudden demand, export bans, and stockpiling. Their scarcity is compounded by problems like limited production capacity and a market dominated by just a few firms.
"The bottleneck is that basically there are these specialized enzymes and specialized primers that you have to make," Davey Smith, co-director of one of the U.S. National Institute of Health's Centers for AIDS Research (CFAR), told RFE/RL. "But, you know, we always had just [enough] capacity to run the tests that we needed. We weren't thinking about scaling up to have to test for a new pandemic."
No Reagents, No Reliable Tests
Central to that great effort to test people en masse is the ability not only to see who is infected -- the emphasis so far as officials tried to contain and then mitigate it -- but also to spot anyone with the telltale antibodies that signal past infection and possible immunity.
The most widely applied tests so far are the so-called RT-PCRs, which start with a swab to collect genetic material that is then extracted, multiplied with polymerases, and amplified in a lab. They use "primers" to target specific sections of genome to show if the coronavirus's RNA, its genetic code, is present in a patient's body.
The second major category of test is serological, separating and scouring blood samples for antibodies generated by past exposure to the virus. It is this less common antibodies test that will be especially important as COVID-19's first wave recedes.
Doctors and policymakers, experts say, will need to learn more about asymptomatic and recovering patients to weigh questions of immunity and vulnerability as they look to relax social-distancing measures and lockdowns.
Both types of test require complex and pure reagents, and plenty of them.
"It's a different kind of chemical that might extract the virus, and then [another to] amplify the virus, and [another to] detect the virus," Smith, who is also a translational research virologist at the University of California-San Diego, said. "But all that chemistry and all those enzymes and salts and buffers are just chemicals that are included [in the PCR test] and called a reagent, and the same sort of thing goes for an antibody test."
'Never Been A Shortage'
The head of a British trade association of coronavirus test-kit manufacturers said recently that "there's never really been a shortage of chemical reagents before now."
But in the face of this pandemic, the British In Vitro Diagnostics Association's Doris-Ann Williams told The New York Times, "all the major countries in the world are wanting the same thing at the same time."
For whatever reason, most countries don't stockpile many reagents despite recent viral epidemics like SARS (2003), MERS (2012, 2015, 2018), Ebola (2014-16, 2019) and Zika (2015-16).
There have been notable exceptions like South Korea, which manufactures and exports test kits after facing a deadly MERS outbreak five years ago.
However, even Seoul couldn't have had all the right reagents on hand for this pandemic before January 10, when a consortium of scientists working from the Chinese epicenter of the virus published an "initial" genome of the latest coronavirus, known officially as SARS-CoV-2.
That's because the necessary primers are essentially lab-grown snippets of genetic code that must match the targeted virus's own genetic material to help extract it.
And by mid-January, China, the world's leading maker and exporter of reagents and coronavirus test kits, was itself scrambling for diagnostic kits to screen for COVID-19 as the outbreak spread in Hubei Province and beyond.
Chinese demand and an export ban dried up global supplies and exacerbated a test-kit shortage that affected responses around the world to the mounting pandemic.
There was a knock-on effect in Europe, the coronavirus's second "epicenter" by March, which quickly fell behind on demand for test kits. It still has not recovered, according to the head of the European Center for Disease Prevention and Control (ECDC), Andrea Ammon.
In the United States, the Centers for Disease Control and Prevention (CDC) blamed "one reagent that isn’t performing as it should consistently" when it hit a major snag rolling out test kits to states in February.
A month later, the head of the CDC warned that reagents essential to test kits "now are in short supply."
Major global test-kit providers have scrambled to boost their own production to feed the lucrative European and North American markets, increasing supply but also crowding out upstart providers of urgently requested test kits and largely excluding poorer countries that can't outbid richer markets.
"We didn't stockpile it. We just relied on our regular testing platforms and they weren't ready for it," Smith said. "I mean, there were multiple mistakes that were made, but one of the biggest ones was that we don't have a stockpile of just those reagents sitting around."