Mordor epidemic: Why do nucleic acids do one moment and antigens for a while?

Image source @ Visual China

Text | Cube Knows the Bureau, author | Li Yun, Editor, | Small materials

In the past week, in addition to the drying basket and refrigerator in the Shanghai WeChat group, the highest appearance rate was a white plastic long block.

Source: People's Daily

The nasal sample is dropped onto a long piece of test strip, and the red bar will change from light to dark. One bar is negative, two bars are positive, and zero bars are invalid.

Today, Testing for nucleic acids or antigens is happening again in Shanghai. Prior to this, there had been two rounds of antigen testing in the Puxi area of Shanghai, which was screened for potentially positive cases as a complement to nucleic acid testing.

The second batch of antigen tests in Puxi region screened more than 10 million people in total. At present, the cumulative antigen detection and sampling in Pudong and Punan, Shanghai has exceeded 18 million.

In China, antigen testing is used as a complementary means of regional nucleic acid testing. Not only in Shanghai, but also in the new round of the new crown epidemic in Hong Kong and Jilin, antigen testing has played a considerable role.

On March 22, the National Health Commission issued the third edition of the Guidelines for the Implementation of Regional Novel Coronavirus Nucleic Acid Testing Organizations. What is different from the first and second editions is that this edition requires the promotion of the monitoring model of "antigen screening and nucleic acid diagnosis".

In other words, nucleic acid test results are still the gold standard, and antigen testing is only a coordinated means of preliminary screening in the region.

At the same time as the introduction of the new antigen detection policy, the accuracy of the reagents has also attracted much attention.

Although the antigen detection result is only 15 minutes, which makes up for the shortcomings of nucleic acid testing that requires a long wait, because the accuracy of antigen detection is lower than that of nucleic acid testing, it is still a supporting role under the prevention and control of the new crown epidemic.

So, why is antigen detection less accurate than nucleic acid testing? Is it a technical problem? How will antigen detection develop in the future? The Cube Knowledge Bureau will answer the questions that are of the greatest concern to these readers one by one.

After reading the article, you will find that today's antigen detection track is like a large audition site. Wanfu Biologics, Novizon, BGI Gene and other products began to enter the domestic market; Jiuan Medical, Oriental Biologics, Mingde Biologics diverted to the sea business, and shared the stage with American companies Abbott and Innova. Regardless of the size of the cast, this was a first for all participants.

01. What are the differences between antigen testing and nucleic acid testing?

The new coronavirus is like a peach, consisting of two parts: a core and a skin.

Nucleic acid detection works by measuring the material in the nucleus, which is the genetic material (RNA) within the VIRUS of COVID-19. The most common method of nucleic acid testing is fluorescence quantitative PCR, which can reverse transcribe RNA from the new coronavirus into DNA, and then copy and amplify it. The specific sequences in the new coronavirus react with the probe and are fluorescently labeled. The inspector determines the amount of virus in the sample through the accumulation of fluorescence signals.

This amplification process takes time, so the time to wait for the test results is generally about half a day to three days. Ideally, the accuracy of nucleic acid testing can reach more than 95%. And nucleic acid testing requires the help of PCR professional instruments, so it can generally only be done in the laboratory.

The object of antigen detection is the skin of the peach, which is where the pathogen protein is located, which Zhang Wenhong likens to "the clothes worn by the virus". The basic principles of antigen detection are based on the reaction of antigen and antibody. The colloidal gold method that is popular on the market now is to place the antibody labeled with colloidal gold on the detection line, as long as the antibody recognizes the invasion of the new crown virus antigen in the sample, it will develop color.

For example, the test for COVID-19 is like hunting:

Nucleic acid detection is the location of prey by means of reconnaissance search; antigen detection is determined by the "click" sound triggered by the trap, thereby determining the presence of prey.

At present, the sensitivity of antigen detection reagents approved in mainland China is about 75%-98%, which is lower than that of nucleic acid detection. The reason is that there is no amplification step for antigen detection, and if the virus content in the sample is not high or the sampling is not successful, a small number of markers in the sample can be captured by nucleic acid detection by amplification, but may be missed by antigen detection. In simple terms, if the prey is light enough, it cannot activate the trap switch.

Antigen testing also has some significant advantages: for example, the reaction time is short, generally less than 15 minutes. It is also very convenient to operate. Antigen testing has been used in various fields since the 1970s. For example, the common early pregnancy test strip in life uses this technology to determine whether to be pregnant by detecting human chorionic gonadotropin in the urine.

Comparison of COVID-19 testing methods

02. What are the current applicable scenarios for antigen detection?

When we have learned that the different methods of new crown virus detection are the choice of factors such as accuracy, efficiency, and accessibility, we must consider the applicable conditions of each time and place when analyzing the applicable scenarios of antigen detection.

On March 18, at the press conference on epidemic prevention and control in Jilin Province, Tong Xueying, director of the Clinical Laboratory Center, gave three main groups of people for which antigen testing is mainly applicable:

The first is a person who goes to a primary health facility and is accompanied by fever symptoms.

This is to take into account the local medical conditions in Jilin Province: from the perspective of the category of primary medical and health institutions, the largest number of local clinics and clinics, health centers, infirmaries, and nursing stations accounts for more than 90% of the primary medical and health institutions in various cities. Only 36 nucleic acid testing services are available in the province. In the case of professionalism, human resources, and weak sampling conditions, antigen testing is the optimal option for initial screening.

The second is to isolate observers.

This segment of the population includes close contacts and residents of the sealed area. At present, Jilin Province has allocated more than 40 million antigen detection kits, accounting for one-sixth of the total population. As of March 26, the total production capacity of nucleic acid testing actually in use in Jilin Province was 1,006,900 tubes. It can be seen that the huge scale of personnel involved in the epidemic determines that accessibility has become an important selection index for testing methods.

The third is community residents who need antigen self-testing.

The Medical Insurance Bureau stipulates that at this stage, antigen testing shall not be higher than 15 yuan per person. In the new test price reduction policy introduced on April 2, the cap price of nucleic acid testing single test is 28 yuan. The low price of antigen testing is also encouraging citizens to take self-prevention of the epidemic outside of official monitoring.

The above applicable groups follow the regulations in the "Application Plan for The Detection of New Coronavirus Antigens (Trial)", that is, this standard applies to the medical network conditions in most parts of the country and the "zero clearance" requirements of the epidemic. Because of the slight differences in its own situation, Shanghai has made slight adjustments while retaining this standard.

The difference lies mainly in the first type of applicable population: the Shanghai Municipal Health Commission said that nucleic acids must be done in fever clinics, and cannot be replaced by antigen testing. This is because institutions with nucleic acid testing capabilities are more common in Shanghai. At present, there are 156 nucleic acid testing institutions in Shanghai, which is 5 times that of Jilin Province.

That is to say, the applicable population of Shanghai antigen testing is mainly concentrated in the second and third categories.

At present, there are two motivations for the use of antigen detection in Shanghai:

The first is to pursue the speed of screening. Especially in the current period of rapid rise in the epidemic situation, antigen screening must be carried out simultaneously with the confirmed nucleic acid.

The second is to detect asymptomatic infected people in the population. Of the new number of patients in Shanghai, up to 98.5% are asymptomatic infected, far higher than 50% of Jilin. Some infected people do not voluntarily go to health facilities, which also allows community antigen testing to cover patients who cannot be reached by nucleic acid testing in hospitals.

The means of antigen detection are inherently flexible in their own way. Therefore, the scope of its application and the problems it solves will also be deformed to varying degrees according to the different situations of the object.

03. Why has the spread of this wave of Omilon put antigen testing in Shanghai on the agenda?

The new coronavirus classification of the current round of epidemic in Shanghai is the BA.2 subtype of the Aomi Kerong variant, which has the characteristics of strong concealment, difficulty in detection, and strong transmission. According to the study, the spread rate of BA.2 was about 30% higher than that of the original Omikeron.

These characteristics make it difficult for potentially infected people to be surveyed through the means of "medical treatment- testing - diagnosis", but must be located through a wide range of investigation. In this environment, the characteristics of cheapness, convenience and speed make antigen detection an important supplementary solution.

04. Why was antigen testing not used during the COVID-19 outbreak in 2020?

A cold knowledge: the development of new crown nucleic acid detection is much simpler than antigen detection.

In January 2020, WHO officially signed a contract to commission pharmaceutical companies to produce nucleic acid tests for COVID-19. Eight months later, the first antigen detection reagent was approved, and the emergency use list procedure was still followed.

The core of nucleic acid detection development is to find specific sequences for COVID-19, then design primer probes for these sequences, and finally perform performance verification. Taking BGI's kit development in the early stage of the pandemic as an example, it took only more than 70 hours from determining the gene sequence of the virus to completing the initial development of the kit.

In contrast, the development of kits for antigen detection is more complex and takes at least two or three months.

As mentioned above, antigen detection technology has been around since the 1970s and has a fool's errand. Why is the antigen test simple for the user not simple for scientists?

Every antigen test requires antigen-specific antibody preparation, which was difficult to obtain in the early stages of the pandemic. Due to the high similarity between the new coronavirus and the SARS virus, the development of early antigen detection mainly relied on antibodies against the SARS virus protein. The process of developing antigen detection reagents is actually a process of comparing, screening, and testing the binding effect of various antibodies and viral antigens. The stronger the binding effect, the more accurate the detection.

For example, the development of nucleic acid detection technology is like making a new pair of shoes for a pair of feet; the development of antigen detection reagents is to choose the one that best fits the foot size in a bunch of shoes. The latter often requires more patience than the former.

Oriental Gene Antigen Detection Kit Source: Company's official website

05. How far are we from open resident antigen self-testing?

On March 13, the first batch of antigen detection kits were launched on Meituan Buy, Baidu Health Mall, and Tmall Health. Although the goods are still in pre-sale, this seems to indicate that the era of self-testing by residents may be coming.

Opening up resident self-testing is to fully open the market for antigen testing. This time, it's not the scientists who are hard, but the suppliers.

The color-developing test strips of antigen detection have high requirements for the antibody activity in the detection area and the speed at which the sample flows through the detection area, which puts forward higher requirements for the quality of the core raw materials of the reagent. In addition to technology, there is also the threshold of production capacity.

At present, many domestic manufacturers have spelled out in order to catch up with the needs of this round of the epidemic. At the end of March, in order to expand production, Mingde Bio added a 20,000-square-meter purification plant, which took only 2 days from factory selection, facilities and raw materials into the factory to trial production.

In this case of saturation of production capacity, if the market for residents' self-testing is completely liberalized, although it will lead to a rapid influx of capital and technology, it may also lead to many problems such as production quality and industry supervision. Antigen detection itself has instabilities in the accuracy of the results, which will also give market space to inferior products.

At present, due to extremely cheap or even free prices, antigen detection kits in Australia, the United Kingdom and other countries have been out of stock, and many pharmacies are in a state of waiting for replenishment. At the same time, due to the public health nature of COVID-19 testing, pricing must take into account the balance between market needs and national planning. Especially in the panic of the epidemic, how to maintain the supply and inventory of public medical institutions under the premise of allowing residents to buy freely still needs a process of discussion and resolution between all parties.

At present, antigen detection kits belong to the regulatory field of four types of drugs, that is, antipyretic, cough, antiviral, and anti-infective drugs. In the past two years, regions across the country are increasing the supervision of the sale of four types of drugs. Many cities require consumers to register their drug purchases, and urge pharmacies to establish their own drug sales accounts, and record the names and quantities of drugs sold one by one in order to clarify the source and flow of each drug.

06. What are the current problems faced by antigen testing?

Accuracy issues are the eternal pain points of antigen detection.

The characteristics of Omikeron also amplify this pain point. The incubation period of the Omikejong virus is relatively short: as short as 1 day, with an average of 3 days, and the longest is about 6-7 days. That is, the time of onset of the patient is advanced. For these affected populations, the reference value of antigen testing is not high, because antigen testing does not adequately respond to low-content viruses early in the disease.

The accuracy problem not only makes the antigen detection basic insulation of the pathogenesis population, but also makes its applicability in low-prevalence areas highly questionable, especially the "false positive problem" in it.

This is because antigen testing is less sensitive and specific than nucleic acid testing.

Sensitivity corresponds to the probability of not missing the test, if 100 positive results, antigen detection can detect 97 positive, the sensitivity of this antigen detection product is 97%; the specificity corresponds to the probability of not misdiagnosis, if the antigen detection detected 100 positive results, 3 are false positive, then its specificity is 97%.

That is to say: in the face of the same group of people, low sensitivity makes antigen detection can detect fewer true positive patients than nucleic acid testing, and low specificity makes antigen test report false positive patients more than nucleic acid testing.

The sensitivity of antigen detection reagents that have been approved in mainland China is between 75% and 98%, and the specificity is between 95% and 99%. In the period of moderate epidemic trend, the prevalence of the population in most parts of China is less than one part per million, and if the 85% sensitive and 97% specific kits are used to screen cities with tens of millions of people, 300,000 positives will be obtained, but only 9 of these 300,000 positives may be true.

At the same time, nucleic acid detection technology is also catching up, vowing to make up for the shortcomings of speed. The PCR amplification reaction in nucleic acid testing lasts up to two hours, and a new technology from Mindy shortens this critical step to 30 minutes. On March 16, the kit was approved for marketing through the FDA's priority review and approval process.

When the weak terms of nucleic acid detection are slowly narrowing the distance with the advantages of antigen detection, the development direction of antigen detection in the future is still ambiguous.

07. What are the main enterprises and products in China's antigen testing industry?

The relevant industrial chain of new crown antigen testing includes: upstream raw materials (including NC film, packaging materials, etc.), midstream product production and manufacturing; downstream terminal sales (pharmacies, inspection agencies, hospitals, etc.). From the perspective of upstream, middle and downstream gross profit margins, the upstream gross profit margin is 90%, the midstream is 60%-70%, and the downstream is 50%-60%.

Among them, the most concerned, and also direct contact with consumers, is the midstream production enterprises and their products.

On March 12, the first batch of 5 antigen detection kits was quite niche compared with 30 nucleic acid kits. As of April 4, the State Food and Drug Administration has approved 24 antigen detection reagent products, and the strong demand for emergency relief is self-evident.

The representative companies approved in China include Wanfu Biologics, Nuowei Zan, BGI Gene, etc., while overseas approved enterprises include Jiuan Medical, Oriental Biologics, Mingde Biologics, etc. In these companies, some of the company's products have both domestic and foreign certification qualifications, but some have only obtained one of them. Given the complex approval process overseas, it is easier to understand products that are only approved in China.

Jiuan Medical is one of the first antigen testing enterprises to go overseas, and it has taken a fancy to the vacancy in the antigen testing market in overseas markets. In this case, in November last year, Jiuan Medical was authorized by the US Food and Drug Administration (FDA) and the antigen kit was authorized for emergency use (EUA). Under the circumstances at that time, the company had to ensure the stable performance of existing orders before entering the mainland market.

It can be seen that in the case of quite tight production capacity, the existing market layout of antigen testing enterprises will determine its priority for emerging markets.

At the same time, the list of approved candidates will be increased rapidly in the future. Shanghai, as an area with a serious epidemic situation, also received the first certified COVID-19 antigen test product in China on April 1. It was after the outbreak of this round of epidemic that The company made a rapid response, combined with the strength of the Shanghai Health Commission and other departments, and completed a series of procedures such as research and development, testing, food and drug administration and EU CE certification in half a month.

In the future, antigen testing enterprises like Shanghai Xinchao that respond to changes in the local epidemic situation will be more and more worth looking forward to. The living force and mobility of local enterprises will directly solve the transportation costs and logistics sealing problems of large-scale antigen testing, and provide guarantees for timely national testing.

08. In which foreign markets has antigen testing been applied? The result?

Beginning January 15, the U.S. government officially implemented the COVID-19 Rapid Test Program. The government sent antigen reagents to the public free of charge, with a monthly demand of 2.6 billion doses, involving a purchase amount of more than 10 billion US dollars.

This is backed by agreements between the U.S. government and insurance companies. Private health insurers will be required to pay for 8 household COVID-19 tests per month for insured persons. U.S. people can purchase home tests for free under insurance, and they can also submit test receipts for reimbursement.

The other two countries that offer free or low-cost testing to the public are the United Kingdom and Germany. In the UK, citizens can apply for free antigen testing up to 7 times a day, and kits are delivered to their homes. In Germany, antigen testing is heavily subsidized, and antigen testing products for less than 1 euro can be found in many grocery stores.

However, in the prevention and control of the epidemic in these countries, antigen testing does not seem to have brought any improvement to the situation.

Last autumn, the UK and Germany failed to limit the spread of the virus in communities, and the rapid rise in indigenous cases predates the rise of Omilon. Japan's antigen self-testing didn't open until last September, after pharmacies were banned from selling medical-grade antigen test kits. But Japan is better at comparing the anglo-German data on new infections, which may be related to the high vaccination rates there.

09. Is there a gap between foreign antigen detection products and domestic products?

Unlike the development process of most industries, domestic antigen detection kits have taken the export route from the beginning.

The antigen testing market in the United Kingdom, the United States and other countries was released earlier than China, and their dependence on the antigen detection market was far greater than that in China. At present, in many Western countries, the "home self-test + home isolation" program is being practiced on a large scale. In January, the United Kingdom declared asymptomatic infected people who tested positive for antigens without having to be confirmed by nucleic acid testing and could begin home isolation.

In China, antigen testing has nucleic acid detection as its bottom; in foreign countries, the proportion of antigen testing independently supporting medical guidance and recommendations is expanding. Therefore, it is like the supporting role suddenly becomes the protagonist, and people's requirements and expectations for it have also risen invisibly.

People want antigen testing products to perform flawlessly, but this requirement is too demanding even for professional actors.

In terms of the performance of antigen detection kits at home and abroad, the two cannot be compared in performance. Because at present, neither side can overcome the swing interval problem of reagent sensitivity. Stories of mistakes, stops, and role changes are played out every day.

Among the first batch of 15 antigen self-testing kit manufacturers approved by the US Food and Drug Administration, there are three Chinese faces of Jiuan Medical, Aikang Biological, and Oriental Biologics.

Abbott and Innova, the two major antigen reagent manufacturers in the United States, have been affected by market opinion because of some accidents.

Among them, Abbott was reported on June 15 last year that antigenic new crown reagent in the Irish survey, only 50% of asymptomatic new crown patients were detected. Its biggest competitor, Innova, has been replaced by Oriental Bio's products since mid-May and has become the main kit for use in the UK.

Innova Antigen Detection Kit Source: Innova official website

Just like the development of antigen detection reagents is a trial and error process - at present, the entire global antigen detection market is also trial and error, and governments are rapidly testing and replacing various products.

The admission ticket for this large-scale audition is not difficult to get, but how to achieve closeness and perfection requires enterprises to have colloidal gold-to-gold technology and labeling technology, immunological technologies such as antigen antibodies, and process optimization technologies.

For Chinese enterprises, it is also a direction worth striving for.

COVID-19 antigen testing belongs to the IVD industry, which is in vitro diagnosis. In fact, until the eve of the outbreak of the new crown epidemic, domestic IVD reagent raw materials have long been highly monopolized by overseas brands. In 2019, the market share of imported products in the domestic IVD raw material market reached 88%. During the epidemic period, the shortage, supply cut and price increase of IVD core raw materials not only exposed supply chain security problems, but also tempered the product capabilities of domestic suppliers.

The same is true of the antigen detection technology test this time, and the short-term effect performance may not be so important - what is important is that the research and development and supply capacity can be improved in continuous re-furnace remanufacturing, thus breaking through the overall bottleneck situation of domestic IVD.

10. What is the future of the antigen detection market?

At present, the market for antigen testing in China is about 10 billion yuan. From a long-term perspective, the market size of antigen detection can reach 270 billion yuan, and the application scenarios of new crown antigen detection will focus on long-term static self-testing and short-term dynamic large-scale detection.

According to the information of the 2020 China Health Statistics Yearbook, 18.3% of China's antigen testing needs come from primary health institutions.

Since 2021, the average monthly volume of confirmed and suspected and asymptomatic people in the mainland has been about 2500 people, corresponding to 8.3% of the demand for antigen testing, while 83% of the market share comes from residents' home self-testing.

It can be said that the current space of China's antigen market mainly depends on the huge base of Chinese mouths, and the huge self-test users that accompany it.

Many people think that the future antigen detection is a hundred billion market, based on this condition. But on top of this, the rapid expansion of the market also relies on another layer of assumptions: that is, the penetration rate of future antigen detection can refer to 80% of the vaccination rate; the frequency of single antigen detection can refer to the current trip code 14 days retrospective period, reaching 2 times a month. In this case, 26.9 billion self-tests are needed every year, which calculates that the self-testIng Chinese market is 268.8 billion yuan.

Therefore, the extent to which China's antigen testing market can grow depends on the changes in government epidemic prevention policies brought about by the changes in epidemic situations under the premise of adhering to the premise of "dynamic zeroing".

End

After the birth of a new product, practitioners must not only consolidate their own areas of strength, but also constantly clarify their technical boundaries.

This is a process in which industry, technology, and capital gradually find positioning. For example, the history of drones can be traced back to the military bombing machines of World War II. This technology solved the problem of the operating cost of aircraft operations at that time, but due to the limitations of fuselage, accuracy, and manufacturing level, it is very recent for UAVs to enter commercial fields such as logistics, plant protection, and surveying and mapping.

For today's antigen detection technology, it may be a good choice to recognize your own matching status and slowly sharpen your strength as a protagonist.