What are the criteria for "herd immunity"? How do I know if I am not infected or asymptomatic? Expert interpretation

Q: The vast majority of people around me are "impotent", is this herd immunity? Will people who are not infected with the new crown still be "yang"?

A: To answer this question, we must first clarify what herd immunity is, and is herd immunity and herd immunity a concept?

A search for the word "herd immunity" on the Internet gives the answer: herd immunity (group immunity), which refers to the resistance of a population or livestock population to infection. A high level of herd immunity indicates a high percentage of animals in the population that are resistant to infection.

I believe that "herd immunity" and "herd immunity" should be distinguished, "herd immunity" is in a relatively stable group, when faced with pathogenic microbial infection, a considerable proportion of individuals in this group through infection or vaccination with effective vaccines to obtain immunity to the pathogenic microorganism, even if there is a source of infection into the group, will not cause persistent infection in the group, this state is to achieve "herd immunity". "Herd immunity" is the proportion of individuals in a group with immunity, and herd immunity can be high or low.

There is a lot of controversy about herd immunity, and even if we talk about this topic now, it will still cause some people's criticism and even abuse. However, many infectious diseases do have this phenomenon, and when a considerable number of people in the group are infected, they gain immunity, and the epidemic gradually stabilizes from the peak of concentrated outbreaks. This herd immunity is not constant, and over time, the immunity in the individual's body declines, or the pathogen mutates. This temporary herd immunity balance was upset, and the epidemic was back volatile.

Different pathogenic microorganisms, the persistence of immunity obtained after infection is different, like hepatitis A virus, a person infected once, generally lifelong immunity, and for the new crown virus, it is currently believed that immunity after infection is not lifelong, some people will be infected a second time, or even a third time. Among them are both reinfection due to decreased immunity and immune escape caused by virus mutation.

Specific to the questions raised by netizens, most of the people around them have passed the yang, is it herd immunity. If the people around you are relatively stable, everyone has been exposed to the new crown virus, the infected have been infected, and this phenomenon of large-scale infection will no longer appear in a short period of time, which can be regarded as temporarily achieving herd immunity.

If some people take very scientific and very strict protective measures such as wearing masks, washing hands frequently, and maintaining social distance, they usually go alone. That is to say, there are still some people who do not have the opportunity to be infected, which is not considered to be post-infection herd immunity. In this case, once personal protection is relaxed, or the source of infection enters the living environment of the person who is alone, someone will be infected.

The second question: will people who are not infected with the new crown still be "yang"?

To answer this question, first analyze the "people who are not infected", which actually includes two main parts. One is really uninfected people, these people have not been exposed to the virus, or contacted, but strong resistance, not infected. The other part of the population is actually asymptomatic infection, this part of the people are infected, but there are no symptoms.

If you are temporarily free of infection due to personal protection or living in a relatively remote environment with little contact with people. This part of the people, a little relaxation of protection, or introduced by the source of infection, will be infected.

If it is highly resistant, it has been exposed to the virus, but has not been infected from beginning to end. This situation is relatively rare for Omicron, but there are such people. Any infectious disease, no matter how contagious, does exist such people who are not easily infected. This resistance is strong, it can be lifelong infection with this virus, or at a certain stage, the body is super resistant. If it is the latter, once the resistance is weakened, it will be infected when it encounters the virus.

In addition, it also depends on the virus, if the next wave of newer variants appears, and this new variant is not resistant to people who were previously resistant, they will become infected.

If it is an asymptomatic infected person, which is similar to a symptomatic infected person, they are actually infected, but they do not know it. In this case, there is a certain immunity in the body. But this immunity is not necessarily long-lasting, and there is a possibility of reinfection in the future.

Source: Source: Dr. Zhang Wei (Researcher of Beijing Center for Disease Control and Prevention, Ph.D., Peking Union Medical College)

Q: I suspect that I am an "asymptomatic infected person", how can I know if I have "impotent"? Do you still need protection?

A: This question is more complex and divided into different situations:

If you judge that you are currently "ongoing" asymptomatic infection, you can use the method of nucleic acid testing, it is best to repeat multiple nucleic acid tests, a single test often missed, false negatives. If the nucleic acid test is positive and you are asymptomatic, it is an infection.

If you judge that "was" yang, it is more difficult and complicated, and it is divided into different situations.

People who have not been vaccinated:

The method of detecting new crown antibodies can be used, mainly detecting IgG and IgM antibodies of the new crown virus. These two antibodies represent different meanings, IgG antibodies last for a long time, generally present and past infections. Positive IgM antibodies are of short duration and generally represent recent infection. However, considering that there are errors in antibody detection after new coronavirus infection, the results will be different for different detection reagents and detection methods. In addition, antibody test results are also disturbed by other diseases and other factors in the body, and false positives or negatives may occur, so they are only used as a reference for whether they are infected.

People who have received inactivated vaccines:

After inactivated vaccination, the type of antibodies produced by the body is similar to that produced by natural infection, and antibodies against viral N protein, S protein, etc. are available. It is not easy to distinguish between natural infection and antibodies produced after vaccination. Especially for people who have been vaccinated for less than three months, it is even less difficult to distinguish.

If the inactivated vaccine has been vaccinated for a long time, for example, more than half a year, or even a year, at this time, the vast majority of antibodies in the human body are reduced. At this time, blood is taken to detect antibodies, and if the antibody titer is high, it is likely to be recently infected.

Vaccinated with a vaccine other than inactivated vaccine:

Such as adenovirus vector vaccine, recombinant protein vaccine, nasal spray influenza virus vector new crown vaccine. These vaccines generally use the S gene of the new coronavirus or part of the S gene, such as the receptor-binding domain (RBD) gene, recombination into the carrier, and synthesize the S protein of the new coronavirus in the human body, or the receptor-binding domain polypeptide protein, or the biosynthesis related protein in vitro, as an antigen (vaccine) to stimulate the human body to produce antibodies against the new coronavirus S protein or receptor-binding domain.

Therefore, people who have received the above non-inactivated vaccines will not have antibodies produced by N protein in their bodies. You can determine whether you have been infected with the new coronavirus by detecting antibodies to N protein.

As mentioned above, antibody detection errors are large, and human antibodies will change over time, which can only be a reference. If you have the conditions, you can measure it. To improve reliability, chemiluminescence testing is preferred.

As for whether protection is needed, before the end of the new crown epidemic, appropriate protection is still necessary, especially for the elderly and people with underlying diseases.

Source: Source: Dr. Zhang Wei (Researcher of Beijing Center for Disease Control and Prevention, Ph.D., Peking Union Medical College)