Can Herd Immunity Protect us from COVID-19?

 

What is herd immunity? Can it protect us from the new coronavirus?

As the number of global cases continues to increase, the World Health Organization has classified the new coronavirus pneumonia as a pandemic.

As efforts to contain the virus seem to have stalled, the British government stated that they hope the country will achieve "herd immunity" to the disease. It means to let the virus spread among people so that enough people will develop immunity to the disease, thereby slowing down and eventually preventing its spread, while protecting the most vulnerable people.

Is prevention of COVID19 really possible through herd immunity?

Herd immunity is also called community immunization, and it is usually one of the measures taken to protect the public from various infectious diseases, including various infectious diseases from measles to influenza.

The basic premise is that the fewer people carrying the virus, the longer it will take for the virus to spread, and the more difficult it will be to spread. 

When enough people develop immunity to pathogens that cause diseases, the entire community will gain immunity against specific diseases. 

This immunity is acquired either because they have been vaccinated, or because they have been exposed to the virus before.

Herd Immunity Chart

But unlike infectious diseases such as measles, there is currently no vaccine against the new coronavirus. Although pharmaceutical companies are eager to produce vaccines, medical experts suggest that it will take at least a year before they can be put into public use.

Now, the only way to develop any form of herd immunity is to expose most people to the virus and develop antibodies themselves. This means the infection of millions or even billions of people.

Is there currently any herd immunity against Coronavirus?

Since this is the first time humans have been exposed to the new coronavirus, there is currently no herd immunity of the new coronavirus, which is why it is so deadly. But if it becomes popular again next year, it may not be so fatal.

This is why governments are now focusing on mitigating disease outbreaks by slowing the spread of disease so that the healthcare system is not overloaded.

These measures include avoiding crowds and maintaining good hygiene habits, such as washing hands frequently for more than 20 seconds.

By restricting social activities, especially social activities with vulnerable groups (such as the elderly and people with low immune function), regardless of whether the person carrying the virus knows it or not, the speed of the virus can be reduced. 

At the same time, this gives the carrier's immune system a chance to speed up, so that the entire population can develop some form of herd immunity.

Also Refer: Vaccine Development Encyclopedia

Once 60% to 70% of the population develops immunity to the new coronavirus, then herd immunity will be developed. At this time, people become less susceptible to infection, and the epidemic will not break out again.

Recently, many articles have analyzed the advantages of different new crown vaccine candidates. The so-called "advantage" is to allow people who have been vaccinated to gain immunity. 

But what exactly is immunity? How can we detect it after we have acquired immunity? 

Simply put, we actually have no way to test immunity. But when we look closely, we sometimes get some clues about immunity.

One clue is the actual antibody response induced after infection. Or to take a step back, it is the antibody response induced by candidate vaccines against such infections. 

But what kind of antibody is it? 

Which parts of the virus or bacteria are responding? 

From the etymological point of view, immunity means exemption, that is, exemption without any response. But in fact, the immune response is just the opposite. It is like being ignited by fire. More precisely, it is an inflammation.

Characteristics of the antibody response induced by the new coronavirus infection

Recently, two papers published in "Science Translational Medicine" (Science Translational Medicine) studied the characteristics of the antibody response induced by the new coronavirus infection. 

Under normal circumstances, the first antibody response is mainly IgM antibody response, and then secondary IgG, IgA and IgE antibody responses will be generated, which help to obtain immune memory. 

However, in the first paper, Delphine Sterlin and others at Sorbonne University tested the acute (short-term) humoral response induced by the new coronavirus infection and found that the main part was IgA antibodies. 

The team not only detected an increase in the number of cells producing this antibody, but also an increase in the total level of neutralizing antibodies in the patient's serum, saliva, and bronchoalveolar fluid. 

In principle, compared to antibodies that are only attached to the surface of the virus, neutralizing antibodies are the ones that can truly neutralize the virus and prevent the occurrence of diseases, rather than just attaching to the pathogen.

What is fake virus?

In practice, the laboratory rarely uses complete viruses. In BSL-2 level laboratories (biosafety level is 2, the highest level is 4) instead of using "fake viruses". 

A fake virus is essentially a weakened virus, so it will no longer pose a real threat. By encapsulating the virus's genome in the protein coat of other viruses, the virus can be weakened. 

Of course, scientists can also modify or inactivate the surface protein of the virus in other ways, or use a helper virus to provide the necessary components alone. 

Generally speaking, once in a susceptible cell, the pseudovirus can only replicate once at most.

The researchers found that although other Ig antibodies were eventually detected, it was IgA antibodies that were responsible for immunity. 

One month after infection, the concentration of IgA in serum dropped significantly, but after 73 days, neutralizing IgA could still be detected in saliva. 

This result raises a key question: 

Which antibody should the vaccine program target to prevent infection or secondary infection?

In another article, Zijun Wang and others from the Laboratory of Molecular Immunology at Rockefeller University also reached a similar conclusion. 

The team further proved that dimer IgA has a stronger neutralizing effect than monomer IgA. Secreted IgA (mainly distributed in the mucosa of the digestive tract, etc.) is mainly in the form of a dimer in which two monomeric IgA are covalently linked together through the J chain. 

Although the paper did not explain why this dimer was formed, it was noted that the subsequent cross-linking process with the spike protein on the surface of the virus can be directly or through other ways to increase the surface affinity to enhance the neutralizing ability of the antibody.

The same seems to be true for IgG antibodies. The monovalent Fab fragments of serum IgG (the part that can bind to the antigen) are far less effective than intact IgG antibodies. 

Compared to IgG antibodies, IgA1 subtypes (dimers) with higher flexibility and longer hinges can better interact with the trimeric spike protein of the new coronavirus.

Study on human leukocyte antigen class II (HLA-II) immune peptides

In fact, in addition to the most critical spike protein receptor binding domain (RBD), scientists have gradually discovered many other possible antibody targets. A recent study on human leukocyte antigen class II (HLA-II) immune peptides on Cell Reoprts showed that dendritic cells in the immune system display peptide fragments covering the entire spike protein. 

The study also found that although the distribution of HLA-II polypeptides is concentrated in 11 locations of most donors, the correlation between these polypeptides and previously predicted polypeptide fragments is very low.

The Research of Proteomics

Like the research of immune peptides, the research of proteomics has attracted people's attention recently. If the volcano map commonly used in mitochondrial proteomics is used to reflect the current research situation, then December 7 is the day of the eruption (several papers were published on this day). 

Then Nature published an interesting paper on the formation of protein dimers (similar to the IgA dimers discussed earlier). Proteins form specific complexes, known as multimerization, which are thought to persist during evolution. 

The classic explanation is that natural selection dictates that the complex structure gives more advantageous functions, thereby increasing complexity. And this study found that there is a simple rule that promotes the evolution of what they call "useless complexity". 

Through the reconstruction of ancestral proteins, the researchers found that the ancient proteins themselves have deep-rooted hydrophobicity (although they failed to explain the deep-rooted reasons), and they are no different from when they are assembled into dimers. 

In other words, protein complexes, such as dimers, do not appear with increased adaptability, but from an "unstoppable" process. They call this process "hydrophobic ratchet".

The mechanism proposed by the researchers is that when an inevitable mutation causes a new hydrophobic region in the protein, the result of ratcheting is to gather the protein together (so that the hydrophobic region can be hidden inside) to form a complex, but this will not add any useful features. 

Since harmful mutations can be effectively hidden on the protein interface, it is even more difficult to get rid of these harmful mutations after the protein becomes a polymer, because they are not exposed to the power of "purification" at all. 

Of course, the premise is that you believe that this mysterious purifying power exists-natural selection will remove those harmful mutations from the population. And now it is only necessary to prevent them from returning to a separate state. If such simple rules promote the occurrence of complexity, after hundreds of millions of years, many useless compounds will be accumulated. So what are the scientists still busy with? 

As biophysicist Luca Turin pointedly pointed out before, "The meaning of proteomics has disappeared in half."

At present, the problem of IgA dimerization needs further study. With the conclusion of the peer review of the new vaccine, whether it is the mRNA vaccine developed by Pfizer and Moderna, or the virus-based vaccine developed by Oxford (University and AstraZeneca, Astrazeneca), they have begun to appear frequently in your circle of friends. But many important issues remain unresolved.

Authoritative figures have even begun to argue about the priority of vaccines, whether the first round of promotion and use of vaccines is reward or punishment? 

For example, many people think that areas that lack medical care and medicine should provide special access to vaccines, but the same many people think that this view is inherently problematic. 

In the Cornell University School of Medicine in the United States, there is even such a statement that any individual of color who believes that they have been treated unfairly in history can privately request an exemption from mandatory vaccine requirements (the United States has historically conducted human trials on blacks). 

Of course, from the overall perspective, vaccine immunization may prove to be invaluable, so some people suggest that everyone should be treated equally, at least when it comes to experimental new vaccines.

 

 Author's Bio

Name: Gwynneth May

Educational Qualification: MBBS, MD (Medicine) Gold Medalist

Profession: Doctor

Experience: 16 Years of Work Experience as a Medical Practitioner

About Me