After receiving the new coronavirus vaccine, will the antibodies in the body be regarded as produced by infection with the virus?

Have you received the COVID-19 vaccine?

After more than a year of hard work, vaccines to combat the new coronavirus are ready to go. Several vaccines have obtained emergency use authorization or have been approved for marketing, and tens of millions of people around the world have completed vaccination.

Some people have started to have new concerns: After getting the COVID-19 vaccine, the body will produce COVID-19 antibodies. Will the nucleic acid and antibody tests be positive? Will they be mistaken for confirmed cases?

Everyone can remember this answer: vaccination will not be considered a confirmed case.

Part 1

How do vaccines help humans prevent diseases?

All of this needs to start with the principles of vaccines and testing. After the virus invades the human body, the immune system can recognize the virus and release antibodies to hold the virus together, making it unable to infect the human body, thereby protecting the body's health.

As early as 1796, humans learned to use this property to fight infectious diseases. We inoculate the human body with the components of the virus that do not make people sick, and we can also produce antibodies against the virus. This is called immunity. The inoculated components are called vaccines.

Novel coronavirus inactivated vaccine

Image source: Xinhua News Agency reporter Zhang Yuwei

With the development of science and technology, humans have developed a variety of ways to quickly and massively prepare vaccines. After the activity of the new coronavirus is eliminated, it can still cause an immune response in the human body, but it cannot replicate in the human body. This is an inactivated vaccine.

Using biotechnology to produce specific components of the virus can also allow humans to gain immunity. This is the method used in recombinant vaccines and vector vaccines.

In addition, there is a new method to make nucleic acid vaccines. Nucleic acid vaccines do not need to be inoculated with the virus components themselves, but only with the templates synthesized by the virus. After the nucleic acid template enters the human body, it turns into virus fragments, giving people immunity.

The human immune system is very "intelligent". When it first senses an antigen such as a virus, it will quickly produce an antibody called IgM to respond to the initial infection. While responding, it will also "remember" the characteristics of the virus to form memory B cells and enter a dormant state. If the virus continues to replicate in the body, or encounters the same virus again, the memory B cells can be reactivated and replicated in large quantities. The reactivated memory B cells will produce a large number of another antibody called IgG. In this process, IgM antibodies are responsible for the initial emergency response, and IgG antibodies are the main force for subsequent reinforcements.

Simply put, the role of the new coronavirus vaccine is to let the body know what the new coronavirus looks like in advance. When encountering the new coronavirus again, the body can produce a large amount of antibodies to eliminate the virus and protect our health.

Schematic diagram of the structure of the new coronavirus

Image source: provided by the author

Part 2

Why can’t vaccination affect the test results?

Patients have antibodies to the new coronavirus, and vaccine recipients also have antibodies to the new coronavirus. When testing for the new coronavirus, will it be considered a confirmed case?

The answer is no.

After vaccination, only a very small amount of IgM antibodies will remain in the body, patrolling like a security guard. When unfortunately infected with COVID-19, the body will quickly awaken dormant memory B cells, and this batch of "reinforcements" can quickly produce a large number of IgG antibodies to fight the new coronavirus. IgM antibodies and subsequent reinforcements of IgG antibodies can help determine whether a person is infected with the new coronavirus.

The current antibody test uses antibody test strips, which can quickly see the results within ten minutes. If you have a certain COVID-19 antibody, you will see a red line at the corresponding position on the test strip. If both antibodies are positive at the same time, there will be two red lines on the test strip, which means that the immune system of a newly infected COVID-19 patient is fighting the new coronavirus fiercely. If only one antibody is positive, further nucleic acid testing is required to determine.

The red lines of the antibody test. The upper line is positive and the lower line is negative.

Image source: Reference 8

It is important to emphasize that this approach is not generally used because of its limitations.
Nucleic acid testing, that is, testing whether the body contains the RNA of the new coronavirus, is currently the main basis for judging whether a person is infected with the new coronavirus in China. In the new coronavirus, RNA is wrapped by the virus's capsid, and there is a layer of envelope outside the capsid. In the three-layer structure, only the middle nucleic acid, that is, RNA, is the target of detection, and the new coronavirus vaccine uses the spike protein of the outermost envelope of the virus. Vaccination will not affect the results of nucleic acid testing.

Nucleic acid detection and nucleic acid vaccine targets

Image source: Reference 7

After understanding the principle of nucleic acid testing, a new question arises. The nucleic acid vaccine mentioned earlier is also nucleic acid. Will the nucleic acid vaccine affect the results of nucleic acid testing?

In fact, the nucleic acid sequence of the new coronavirus has a total of about 30,000 bases, and only about 4,000 bases are used for nucleic acid vaccines. In order to ensure the accuracy of nucleic acid testing, it is usually necessary to test two positions of the new coronavirus nucleic acid. These two positions are not on the nucleic acid vaccine, so they will not affect the nucleic acid test results. Some nucleic acid test kits will test a single position or three positions, which still do not overlap with the nucleic acid vaccine.

In addition to the non-overlapping base positions, the fluorescent PCR test used for nucleic acid detection is a sensitive technology that can not only detect the nucleic acid of the virus, but also the amount of viral nucleic acid. This can also determine whether the vaccine has been injected or the virus has been infected.

The COVID-19 vaccine and treatment plan have been perfected by countless scientists and medical workers. Antibody testing, which is less accurate but more convenient, cleverly sets strict regulations for two antibodies, accurately detecting any trace of the virus. Nucleic acid testing, as the gold standard, does not confuse people who are actually infected with the COVID-19 vaccine because the vaccine does not contain viral nucleic acid.

Therefore, after being vaccinated, you can safely cooperate with quarantine personnel in every nucleic acid test or antibody test without worrying about being mistaken for an infected person.

Even if you have the "luck" of winning the lottery and accidentally encounter a false positive in one test method, the tester will ask you to re-test more strictly. At this time, you don't need to be anxious or panic. Just trust the medical staff and wait patiently for the results.

References:

[1] Sprint! my country's five new coronavirus vaccines undergo phase III clinical trials. Xinhua News Agency. December 16, 2020.

[2] Novel Coronavirus Pneumonia Diagnosis and Treatment Plan (Trial Version 8). National Health Commission.

[3] COVID-19vaccines. FDA. https://www.fda.gov/emergency-preparedness-and-response/coronavirus-disease-2019-covid-19/covid-19-vaccines

[4] Authoritative release by the Joint Prevention and Control Mechanism of the State Council. December 19, 2020.

[5] Kim, Dongwan, et al. "The architecture of SARS-CoV-2 transcriptome." Cell(2020).

[6] MessengerRNA encoding the full-length SARS-CoV-2 spike glycoprotein. WHO InternationalNonproprietary Names Programme. September 2020

[7] Yang Siyuan, Wang Han, Yu Fengting, et al. Clinical application of novel coronavirus nucleic acid detection methods[J]. International Journal of Virology, Vol. 27, No. 5, pp. 425-428, ISTIC, 2020.

[8] Zhang Sai, Xiang Le, Li Linhai, Li Huijun, Wang Gang, Qian Chungeng. Development and performance evaluation of novel coronavirus (2019-nCoV) IgM/IgG antibody detection reagents[J]. Chinese Journal of Biotechnology, 2020, v.40;No.341(08):6-14.

Produced by: Science Popularization China

Produced by: Zhiyao

Producer: Computer Network Information Center, Chinese Academy of Sciences

(The images with source indicated in this article have been authorized)

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