In order to contain it, researchers must first collect data about who's been infected.

為了控制住疫情，研究員首先必須收集資料，了解受感染的是哪些人。

Two main viral testing techniques are critical: one tells you if you have the virus and the other shows if you've already had it.

有兩種主要的病毒檢測技術非常重要：一種能判斷你目前身上是否有病毒，另一種則能顯示你是否曾經染上病毒。

So, how exactly do these tests work?

這些檢測的原理到底是什麼？

PCR, or polymerase chain reaction testing, targets the virus's genetic material in the body and is used to diagnose someone who is currently infected.

聚合酶連鎖反應 (PCR) 檢測針對病毒在人體內的遺傳物質，可用來診斷受測者目前是否受到感染。

Yet, this genetic material may be present in such imperceptible amounts that actually detecting it is difficult.

但，這種遺傳物質的量可能非常微小，微小到很難偵測到。

This is where PCR comes in: it's widely used to amplify genetic information to large enough quantities that it can be readily observed.

此時 PCR 就派上用場了：PCR 被廣泛應用在將遺傳資訊放大到可以很容易觀察到的程度。

To develop a PCR test for a never-before-seen virus, researchers first sequence its genetic material, or genome, and identify regions that are unique to that specific virus.

若要針對前所未見的病毒來開發 PCR 檢測，研究員首先得要對該病毒的遺傳物質，即基因組，做定序，並且找出該病毒與其他病毒不同的區域。

PCR then targets these particular segments.

接著，PCR 會把目標放在這些特定區域上。

A PCR test begins by collecting a sample: this can be blood for hepatitis viruses, feces for poliovirus, and samples from the nose or throat for coronaviruses.

PCR 檢測一開始要先收集樣本：肝炎病毒可以用血液樣本，小兒麻痺病毒可以用糞便樣本，冠狀病毒可以用取自鼻子或喉嚨的樣本。

The sample is taken to a central laboratory where PCR is performed to test for the presence of the virus' genome.

樣本會被送到中央實驗室，在那裡進行 PCR，來檢測是否有該病毒的基因組。

Genetic information can be encoded via DNA or RNA.

可以透過 DNA 或 RNA 來做基因資訊的編碼。

HPV, for example, uses DNA, while SARS-CoV-2, the cause of COVID-19, uses RNA.

舉例來說，人類乳突病毒用的是 DNA，而引起 2019 冠狀病毒的 SARS-CoV-2 則用 RNA。

Before running the PCR, the viral RNA, if present, must be reverse transcribed to make a strand of complementary DNA.

在進行 PCR 之前，病毒的 RNA ——如果有的話—— 必須要經過反轉錄， 來製造一股互補 DNA。

Researchers then run the PCR.

接著，研究員會進行 PCR。

If the virus is present in the sample, its unique regions of genetic code will be identified by complementary primers and copied by enzymes.

如果樣本中有病毒，其獨特的遺傳編碼區域就會被互補的引子辨視出來，並被酵素複製。

One strand of DNA becomes hundreds of millions, which are detected using probes marked with fluorescent dye.

一股 DNA 就會變成數億股，會被帶有螢光標記染料的探測器偵測到。

If the PCR machine senses fluorescence, the sample has tested positive for the virus, meaning the individual is infected.

如果 PCR 機器感測到螢光染料，樣本對該病毒的檢測結果就是陽性，意即受測者受到感染。

Immunoassays, on the other hand, tap into the immune system's memory of the virus, showing if someone has previously been infected.

另一方面，免疫分析檢測的是免疫系統對病毒的記憶，顯示受測者是否曾經被感染過。

They work by targeting virus-specific antibodies generated by the immune system during infection.

原理是，受到感染時，免疫系統會針對不同病毒產生出不同抗體。

These are specialized classes of proteins that identify and fight foreign substances, like viruses.

這類抗體是有專門功能的蛋白質，能夠辨視出、對抗外來物質，如病毒。

Immunoassays may detect IgG antibodies, the most abundant class, and IgM antibodies, the type that's first produced in response to a new infection.

免疫分析可偵測到 IgG 抗體， 這類抗體是最充足的抗體，及 IgM 抗體，在因應新感染時最先產生出來的抗體。

The presence of IgM antibodies suggests a recent infection, but since it can take the body over a week to produce a detectable amount, they're unreliable in diagnosing current infections.

若有發現 IgM 抗體， 就表示近期有受過感染，但因為身體至少要一週才能產生出偵測得到的抗體量，若想診斷目前是否有受到感染，這種方式並不可靠。

Meanwhile, IgG antibodies circulate for an extended period after infection; their presence usually indicates that someone was exposed and recovered.

同時，在感染過後，IgG 抗體還會額外在體內循環一段時間；發現這種抗體通常是表示受測者曾經接觸病毒且已復原。

Before the immunoassay, health professionals draw blood from an individual.

在進行免疫分析之前，健康專業人士會幫受測者抽血。

This sample then comes into contact with a portion of the virus of interest.

接著讓血液樣本和一部分要檢測的目標病毒做接觸。

If the body has, in fact, been exposed to the virus in the past, the body's virus-specific antibodies will bind to it during the test.

如果受測者過去曾經有接觸過這種病毒，在檢測時，體內針對這種病毒產生的抗體就會和病毒結合。

This reaction produces a change in color, indicating that the sample tested positive and that the individual has been exposed to the virus.

這種反應會造成顏色改變， 表示樣本檢測的結果為陽性，也就是該受測者曾經接觸過病毒。

Immunoassays are especially important when it comes to retroactively diagnosing people who were infected but went untested.

免疫分析特別重要的應用是：回溯診斷曾經受過感染卻沒有被檢測出來的人。

And there's exciting potential for those who have developed immunity to a virus: in some cases, their blood plasma could be used as treatment in people who are currently fighting it.

如果有人已經有可以抵抗病毒的免疫力，那是很讓人振奮的：在某些情況下，可以把他們的血漿拿來治療還在和病毒奮戰的人。

PCR and immunoassays are always in the process of becoming more accurate and efficient.

PCR 和免疫分析的準確度和效率一直都不斷在提升中。

For example, innovations in PCR have led to the use of self-contained testing devices that relay results within one hour.

比如，在 PCR 的創新上，已經出現了獨立檢測裝置，可以在一小時內得到結果。

Digital PCR, which quantifies individual pieces of target DNA, shows promise in further boosting accuracy.

數位 PCR 可以量化目標 DNA 的個別片段，未來有很好的前景， 能將正確率大大提升。

And although immunoassays are difficult to develop quickly, researchers in Singapore were able to create one for SARS-CoV-2 even before COVID-19 was declared a pandemic.

雖然免疫分析的發展很難快得起來，但新加坡的研究員已經能夠針對新型冠狀病毒建造出免疫分析，且時間還是在宣佈新型冠狀病毒大流行之前。

These tests, along with the scientists who develop them and the health professionals who administer them, are absolutely essential.

這些檢測—— 及開發它們的科學家，和管理測試的健康專業人士—— 都是非常重要的。

And when deployed early, they can save millions of lives.

如果能及早拿來實際應用， 數百萬人可能會因此得救。

We know that our bodies produce virus-specific antibodies, but how?

我們知道我們的身體會產生特定病毒的抗體，但是是怎麼產生的？

Learn more about your bodies defenses with this video, or find out how a very different medical test works with this one.

透過這支影片學習更多關於你的身體防禦機制，或在這支影片學到非常特別的醫療檢查。