‘Antibodies are the most powerful weapon in the fight against COVID-19,’ says Dr Arun Sharma of ICMR-Jodhpur

Antibodies are the most powerful weapon in defeating the coronavirus, and vaccines provide long-term immunity by generating adequate antibodies in the body. Natural infection also leads to the formation of antibodies, providing protection against reinfection to some extent. Dr Arun Sharma, community medicine expert and director of the National Noncommunicable Disease Implementation Research Institute-ICMR, Jodhpur, explains the relationship between infection and antibodies, when and whether to check the presence of antibodies and how they help fight the virus.

What is the relationship between infection and antibodies?

When a new virus affects a population, the body’s immune system recognizes it as a foreign body and develops antibodies against it. Since antibodies take a long time to develop, infection causes serious illness, depending on the pathogenicity of the virus, viral load, immunity of the person, etc. But when the same pathogen strikes the next time, the antibodies, which are already in the body, quickly activate and the severity of the disease decreases.

For example, rotavirus affects the digestive system. It was observed that in the 1990s it caused severe diarrhea in children, but gradually children developed antibodies against this virus and the severity of the disease decreased. But then it started to affect foreign travelers to India because they were not exposed to the virus in their country. So, this is how a new virus works unless it mutates to become more transmissible or pathogenic.

What is the ideal time interval after vaccination to check a person’s level of antibodies for COVID-19? Which test to choose?

Any well-equipped pathology laboratory can test for the presence of antibodies in the blood. There are two types of antibodies generated in the body in response to infection – the initial response is with IgM, which remains for a short time, and later the body produces IgG antibodies. So, soon after infection with COVID-19, the IgM level is high, but these antibodies wear off after six weeks. IgG antibodies could be detected after two to three months. After vaccination, if we want to know if the vaccine led to the production of antibodies, we must opt ​​for IgG.

Immunity is of two types: humoral and cell-mediated. In diseases like polio, hepatitis or Covid-19, antibodies in the blood fight infection, while in diseases like tuberculosis, cell-mediated immunity has more of a role to play. Basically, there are mainly two types of immune cells: B cells, which form antibodies in the blood (humoral antibodies), and T cells, which are responsible for cell-mediated immunity. T cells kill and devour the disease causing pathogen, while antibodies in the blood neutralize the pathogen by binding to its disease causing protein, not allowing it to enter the human cell. . For example, in COVID-19, the antibodies bind to the spike protein present in the virus, which helps the virus enter the cell, where it replicates. The antibodies ensure that the disease does not get worse.

Some experts say vaccines lead to long-term cell-mediated immunity. Can you explain what this means for ordinary readers?

There are two types of T cells: helper T cells and suppressor T cells. Helper cells recognize and memorize antigen and help B cells quickly reproduce antibodies if re-infected. COVID-19 vaccines help helper T cells memorize the antigen. And when a person catches the infection, these helper cells help the B cells make antibodies against them. They stay active longer.

Should we do an antibody test after vaccination? Why do some people not develop antibodies after vaccination?

Whether or not to have the antibody level tested after vaccination or natural infection is an individual choice. For people in whom antibodies do not form after vaccination, I would recommend a thorough medical investigation. I think it could be a person’s genetic makeup or issues with the immune system that can lead to such a situation.

Why do some people still develop the disease, called breakthrough infections, even after the two doses of the vaccine?

COVID-19 vaccines stimulate the body to develop antibodies against the virus. But these antibodies remain in the blood. SAR-Cov-2 enters the body through the mouth and nose. It replicates there, then through the trachea, enters the lungs. Thus, the antibodies can neutralize the virus once it passes from the lungs to the blood. Thus, as soon as the virus enters the blood, the antibodies attack it and prevent it from entering other organs such as the brain, heart or kidneys. The virus can cause infection, but vaccines prevent it from causing serious illness or hospitalization. This is why we insist on following appropriate COVID behavior even after taking the vaccine.

A nasal vaccine can help kill the virus in the nasal passage itself. This happens with oral polio vaccine. A weakened viral vaccine, when given orally, forms a protective layer around the intestine. This coating does not allow the virus to cause infection.

How accurate are serological surveys?

The serological survey is a research methodology that helps decision makers develop strategies to fight the pandemic. It is done by random sampling to know the prevalence of antibodies in the population. These antibodies tell us the extent of the infection. But it has its limitations because the sample size is small and cannot represent the entire population of a large country like India. So we cannot and must not let our guard down.