Vaccines provide long-term immunity by generating antibodies, says Dr Arun Sharma of ICMR, Jodhpur
Antibodies are the most potent weapon to beat coronavirus and vaccines provide long-term immunity by generating adequate antibodies in the body. Natural infection, too, leads to antibodies formation, giving protection against the re-infection to an extent. Dr. Arun Sharma, a community medicine expert and Director, National Institute for Implementation Research on Non-Communicable Diseases-ICMR, Jodhpur, explains the relationship between the infection and antibodies, when and whether to check the presence of antibodies and how they help fight the virus.
What is the relation between infection and antibodies?
When a new virus affects a population, the body’s immune system recognises it as a foreign body and develops antibodies against it. Since antibodies take time to develop, the infection causes a severe disease, depending upon the pathogenicity of the virus, virus load, immunity of the person, and so on. But when the same pathogen strikes the next time, the antibodies, which are already present in the body, get activated fast and so the severity of the disease reduces.
For example, rotavirus affects the digestive system. It was observed that in the 1990s it used to cause severe diarrhoea in children but gradually children developed antibodies against it and the severity of the disease came down. But then it began to affect the foreign travellers to India as they were not exposed to the virus in their countries. So, this is how a new virus works unless it mutates to become more transmissible or pathogenic.
What is the ideal time interval post-vaccination to check the level of antibodies for COVID-19 in a person? Which test should one opt for?
Any well-equipped pathology laboratory can test 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 through IgM, which remains for a short duration, and later the body produces IgG antibodies. So, soon after the COVID-19 infection, the level of IgM is high, but these antibodies fade after six weeks. IgG antibodies could be detected after two to three months. After vaccination, if one wants to know if the vaccine has led to antibodies production, they should go for IgG.
Immunity is of two types: humoral and cell mediated. In diseases such as Polio, Hepatitis or Covid-19, antibodies in the blood fight the infection, whereas in diseases such as tuberculosis, cell-mediated immunity has more role to play. Basically, majorly there are two types of immunity cells — B Cells, which form antibodies in the blood (humoral antibodies) and T-Cell, responsible for cell-mediated immunity. The T-cells kill and eat up the disease-causing pathogen, while the antibodies present in the blood neutralise the pathogen by binding to its disease-causing protein, not allowing it to enter the human cell. For example, in COVID-19, antibodies bind to the spike protein present in the virus, which helps the virus enter the cell, where it replicates. Antibodies ensure that the disease does not become severe.
Some experts say that vaccines lead to long-term cell-mediated immunity. Can you explain what it means for common readers?
There are two types of T-cells: T-helper cells, and T-suppressor cells. The helper cells recognise and memorise the antigen and help the B cells to reproduce the antibodies quickly in case of re-infection. COVID-19 vaccines help the T-helper cells to memorise the antigen. And when a person catches the infection, these helper cells help the B-cells in making antibodies against it. They remain active for a longer time.
Should one go for antibody testing post- vaccination? Why do some people not develop antibodies post-vaccination?
Whether or not to get antibody level tested post-vaccination or natural infection is an individual choice. As far as people in whom antibodies are not formed post-vaccination are concerned, I would recommend a thorough medical investigation. I feel it could be a person’s genetic composition or immune system-related issues that can lead to such a situation.
Why do some people still develop the disease, so-called breakthrough infections, even after the two doses of Vaccines?
The COVID-19 vaccines stimulate the body to develop antibodies against the virus. But these antibodies remain in the blood. The SAR-Cov-2 enters the body through the mouth and the nose. It replicates there and then through the trachea, enters the lungs. So, antibodies can neutralise the virus once it moves from the lung to the blood. So, as soon as the virus enters the blood, the antibodies attack it and prevent it from entering other organs such as the brain, the heart, or the kidney. The virus can cause the infection, but vaccines prevent it from causing severe disease, or hospitalisation. That’s why we emphasise on following COVID-appropriate behaviour even after taking the vaccine.
A nasal vaccine may help kill the virus in the nasal track itself. This happens in the case of the oral polio vaccine. A weakened virus vaccine, when given orally, forms a protective coating around the gut. This coating does not allow the virus to cause the infection.
How accurate are sero surveys?
Sero-survey is a research methodology that helps policymakers come up with strategies to fight the pandemic. It is done through random sampling to know the prevalence of antibodies in the population. These antibodies tell us the extent of infection. But it has its limitation as the sample size is small and cannot represent the entire population of a large country like India. So, we cannot and should not lower our guard.