We are aware that there are many vaccines already in use and many more under trial stages at the time when we are publishing this blog. It will be wise if we understand the strategy being used to fight this deadly pandemic. This will give us confidence as well as remove all apprehensions towards the vaccination drive which is so important to reach herd immunity.
Until now there have been three possible ways in which vaccines have been able to generate an immune response. It can produce B-cells or T cells or simply both.
The B-cell-based response is quick to act however with time fades away. B-cells attack the virus directly but unfortunately, they are short-lived. Hence vaccines are designed to have multiple doses in terms of securing the response especially in times when the virus is prevalent. Luckily though, a person vaccinated or infected by the virus develops ‘Memory’ B cells. These help a rapid antibody response if infected again. To build optimistically sufficient quantities of these cells a yearly or six-monthly booster dose might be required in some cases.
However, we need to protect ourselves for the long term and hence we need this ability in our vaccine. Our immune system’s second line of defense is T-cells. These T-cells are more of killer cells. They do not attack the virus but kill the cells which are infected by the virus. This inhibits the multiplication of the virus. Again it is important to have sufficient T-cells. Since these, unlike antibodies are difficult to measure, we need to ensure that sufficient stimuli are given for its generation. Hence multiple doses of vaccination are required. Vaccination even after the infection is important although one can take the vaccine after 4 to 6 weeks of recovering from infection.
There have been many studies to timeline this existence of long-term T-cells and ‘Memory’ B-cells in those cases who were infected with Covid-19. Data gave out that even after six months patients had elevated levels of T-cells. Virologists had earlier conducted studies on the SARS virus from 2002 to 2005. They found the T-cell immunity present for up to 10 years. Thus our vaccination will be more decisive and long-term if we can generate both ‘memory’ B-cell and T-cell response. This consideration has been there behind every vaccine being used currently to fight Coronavirus. However, as of now, the data is insufficient to completely chart the long-term response. Researches and studies are still on as we write to find the most suitable answer to a perfect vaccine.
As we are noticing that virus strains are changing due to mutation. The vaccine generally is designed to fight a single virus strain. However since there is sufficient similarity most of the time between different mutations, the initial B-cell response is good in those cases who have either been infected by some other strain of virus or have been vaccinated. Therefore till such time we have a pandemic and strains are challenging us, we need to keep our B-cells army strong. Hence it gives out the reason why we need two doses of vaccine and also we may require a yearly booster dose. As mentioned above, research is still on and many vaccine manufacturers are proposing a single-dose vaccination which will not only make sufficient ‘Memory’ B-cells and T-cells to fight the infection but also prevent limited but multiple strains.