Why High Antibody Doesn’t Guarantee Protection From Covid-19

The purpose of the current vaccination drive is to provide protection from Sars_Cov_2 that causes Covid-19. However, in the second wave, many such cases have come up in which people have contracted the virus a few weeks after taking both doses of vaccines. A few of them have died also.

Though a vaccine helps produce antibodies in advance to fight against the virus yet every individual doesn’t develop the same amount of it after vaccination.

Doctors say that the amount of antibodies that vaccination will produce in an individual depends on his or her immune system. The quantity of antibody is measured by its titer value and a higher titer value means more antibody in a person.

Now the question is, “Is there a benchmark for antibody level beyond which the virus will not cause any infection?”

Unfortunately, vaccine scientists and infectious disease experts say that a higher titer value doesn’t always guarantee complete protection and that’s the reason even a fully vaccinated person contracts the disease.

Let’s understand why it is so?

Sars_Cov_2 virus is a non-cellular microscopic organism that can multiply in a living cell. It has a spike protein protruding from its surface. This spike protein has a receptor-binding domain (RBD).  

On the other hand, human beings have ACE2 receptors in some of their cells. These cells are found in the nose and other body parts like the heart, kidney, lungs, etc. The spike protein’s RBD gets attached to the ACE2 receptor and that’s how Sars_Cov_2 enters the human body.

Experts say that only those antibodies that are specific to RBD can help provide protection. These antibodies cannot be measured through a titer score.

They say that titer measures a general antibody that our body produces against any antigen.

Let’s understand how the body reacts to natural infection.

According to experts, when Sars_Cov_2 infects a human being, the body develops the first antibody, Immunoglobulin M or IgM, to fight against the virus.

Between 5 to 10 days of illness, the body develops four other antibodies – (a) Immunoglobulin G, (b) neutralizing antibody, (c) anti-spike antibody, and (d) RBD specific antibody.

“One needs to understand the main antibody which prevents the Covid infection, is the RBD specific antibody. The second in importance is neutralizing antibodies which protect from the virus," Dr Samrat D Shah, internal medicine specialist and honorary internist to the Governor of Maharashtra, said.

He adds, “So if you develop antibodies towards RBD, it gives you more immunity as compared to other antibodies. It cannot be measured through titer value. Very few laboratories have just recently started doing RBD specific antibody tests.”

Doctors and researchers say that three to six months after natural infection, an individual loses all-natural antibodies. However, despite that, the cases of reinfection are very few and far between.

“B cells and T cells in the human body memorize the antigen and the moment the same virus infects the body, they make antibodies specific to target the virus. That’s why reinfection is very low and even if it occurs, the severity is not as high as it was during the first infection,” Noted epidemiologist Dr Jayaprakash Muliyil said.

Outlook recently published research by Gyaneshwar Chaubey, a professor of genetics at Banaras Hindu University (BHU) whose pilot study on 20 volunteers showed that the first dose of coronavirus vaccine helps develop antibodies among Covid-19 recovered persons faster compared to those people who never contracted the virus.

Prof Chaubey‘s study is consistent with the views of many noted epidemiologists and doctors who believe that an individual memory a cell can immediately activate an antibody specific to target the antigen.

That’s why a section of the experts is not in favour of vaccinating the Covid-19 recovered population. Many experts say that natural antibodies are better than vaccine-acquired antibodies.

Based on their anecdotal experiences, they say that when people get vaccinated, they don’t develop all four antibodies discussed above.

“I can say based on my experience that vaccines don’t help develop RBD-specific antibodies. That’s why people remain vulnerable to infection,” Dr Shah said.

He added, “Let’s take for example an individual who takes the Covishield vaccine. It makes anti-spike antibodies that prevent the spike protein to enter and bind to the ACE2. But the strength of the binding is dependent on RBD specific antibodies, not the anti-spike.”

Dr Shah says that if an individual acquires high anti spike antibodies but doesn’t get RBD-specific antibody, he remains susceptible to get the infection.

Dr. Syamal Roy, a noted immunologist, who retired as Head of the Department of Infectious Diseases and Immunology, Indian Institute of Chemical Biology, Kolkata seconds Dr Shah that its RBD specific antibodies that can stop ACE2 receptor to bind with spike protein.

“I think it is still a subject of research whether vaccine produces RBD specific antibodies or not. Since there is no study in this regard, it is difficult for me to answer,” Dr Roy said.

Dr Muliyil, who also supports the superiority of natural antibody over a vaccine-acquired antibody, says that human response to a virus is very complicated as it triggers a whole lot of immune response to sterilize the body.

He says that the virus enters the body through the throat which has tonsils, adenoids, and a lot of other glands and defence mechanisms.

“When a vaccine is given intra-muscular, those particular glands are not specifically activated. So, when the virus comes and sits on your throat, it doesn’t respond furiously immediately,” Dr Muliyil said.   

He added, “A person may develop a mild infection but since the vaccine makes the body respond adequately, serious illness or death is very rare.”