Important Aspects of the Epidemic Vaccination Program
Suppose we continue to review the history of the world from time to time. In that case, we will see that not only human beings but also animals have been affected innumerable times by various epidemics. Major epidemics such as Justinian Plague, The Black Death, The Great Plague, Cholera, Yellow Fever, Spanish Flu, Asian Flu, Ebola, etc. have claimed billions of lives. Every plague has pointed the finger at us. No matter how civilized we may be, we are as helpless to nature as ever.
The typhus epidemic in Greece, the center of ancient civilization, killed nearly two-thirds of Athens’ population. The bubonic plague killed about 50 million people or about 26 percent of the population at the time. In 1350, about one-third of the world’s population died in the plague known as The Black Death. It is estimated that between 1817 and 1821, about 870000 people died of cholera in the Indian subcontinent. Mentioning the death toll in other epidemics will only increase writing scope. However, the reality is that from that mythical time till today, various epidemics have taken away innumerable lives from the earth.
Almost all of the world has been under house arrest for the past few months due to the recent novel coronavirus scare. A deep uncertainty has engulfed the whole world. Yet people do not stop hoping for a better future.
Just as doctors, law enforcement officers, and volunteers are working day and night to defeat the virus, scientists worldwide are constantly researching ways to find an effective vaccine to prevent the virus. Hopefully, in such a short period of time, a total of 56 vaccines against coronavirus have been developed at the clinical research stage. There are 40 vaccines in the first-second clinical stage. The remaining 16 are in the second and third clinical stages. These studies also show that vaccines that pass the third stage have been shown to be about 95 percent effective against coronavirus in some cases.
So we can say now that the vaccine is almost gone! But the problem is that it is not possible to produce such a large amount of vaccines overnight, given the current needs of the world’s population.
The big question now is, how will the insufficient amount of vaccines be distributed worldwide? We have started to know about each model of different countries’ own immunization programs through various newspapers, media, and online. However, the basic basis or controller of making these models is almost the same.
Today, we will learn about the mathematical model behind making these models. The main role of these models is that they provide a strong explanation of the current potential of an event or process as well as its future dynamics. Models also play an important role in understanding infectious diseases. Models can range from simple ‘SIR Model’ with only three variables to sophisticated simulation models with millions of variables.
The transmission of a viral pandemic depends on the reproductive number of the virus ‘R₀.’ If R₀ is zero, then the virus does not spread from one person to another. If the reproductive number, ‘R₀ = 1’, then the virus will only be transmitted from one person to another. But if the number is more than one (R₀> 1), then the virus is spreading at an ‘exponential’ rate.
Again, the reproductive number for different viruses, R₀, may vary depending on the different media. For example, the HIV virus can only be spread through the blood, semen, etc. Of an infected person. Therefore, the reproductive number R₀ of this virus is limited to these mediums only. In the case of air, water, etc., the reproductive number of HIV virus, R₀ value is zero.
It must be borne in mind, however, that in the case of an epidemic, reproductive numbers alone cannot reflect all the complexities of an epidemic. It gives a minimal idea of how fast the virus is spreading or spreading among a country’s population.
When a country’s Ministry of Public Health plans its immunization program, it must keep in mind the percentage of the total population at risk of infection, the seriousness of the risk and the minimum percentage of the total population in a country to prevent a major epidemic. Have to bring In addition, they aim to limit the spread of the infectious virus, to reduce the rate of spread of the viral infection or to bring the reproductive number R6 to the smallest possible meaning; So that the spread of the infectious virus can at least transform from ‘exponential’ to ‘linear’ growth.
The difference between exponential and linear growth
An increase is called a linear increase if it continues to grow at the same rate at intervals of time. If so, a single tree can grow up to 50 cm per year. The growth of the tree is called linear growth. But if it were said, the tree’s growth per year would be twice as much as the previous year? In that case, after thirty years from today, what is the tree’s height? Can you guess?
Well, let’s not talk about tree growth. Now let’s try to explain the matter by spreading a news. Suppose a secret news is known only to one person. He once decided that he would not keep the news to himself. But every day he will tell only one person about the news. But if only one person knows the news today, two will know tomorrow. The next day, three people will know. In this way, day by day, one by one, the number of people who will be aware of the news will continue to increase. As such, only 30 people will know the news after one month or 30 days. In this case, the whole process of spreading the person’s news will be called linear growth.
But what if that person would tell that news to two more people every day? But four at the end of the second day, eight at the end of the third day, and if it continues like this day after day, about a billion people will be aware of the news in a month. Surprisingly, if you persevere for one more day, you will see that almost all the people of the world will be in the same picture when it comes to news! In the case of news dissemination, the second process is much faster than the first, which is exponential growth.
Viral infections spread significantly only when the reproductive number is more than one (R₀> 1). In the case of some viral infections, such as influenza, the R₀ value is usually 2 or 3. It is about 5 in case of mumps and 12 to 18 in case of measles.
Now, if a viral infection suddenly causes a major epidemic in the world and we also have an effective vaccine to prevent it, the production of which is again inadequate compared to the needs of the present population; In that case, the main objective of the immunization program would be to reduce R8 to 1 so that the viral infection does not get the chance of exponential infection.
Suppose, coronavirus infection rate or reproductive number 3. Now, if a person infected with coronavirus participates in a social event where he came in contact with a total of 30 people. However, it is estimated that only three of the participants will be infected with the coronavirus. And the chances of everyone else getting infected will be around 10 percent.
If the coronavirus reproductive number is to be reduced from 3 to 1 by vaccination, two out of every three people in a country, or about 66.67 percent, will need to be vaccinated. As such, at least 20 of the participants in the program must be brought under the Covid-19 vaccination program. As a result, the rate of spread of coronavirus will change from exponential to linear growth.
A recent analysis of research papers of various individuals and organizations shows that the coronavirus spread rate or reproductive number in Bangladesh is 1.87 and the transmission of the virus is exponential in some parts. Given the uncertainty, inadequacy and economic issues that exist in the current context of vaccination in Bangladesh, it should not be difficult for anyone to understand that the Bangladesh government may not be in a position to bring its entire population under the immunization program at once.
However, in order for Bangladesh to take a strong stand against the coronavirus, the virus should be reduced to 1. Although the coronavirus infection rate in Bangladesh is lower than that of neighboring India (2.56), in order to produce antibodies against the virus in a large population, about 55% of the population must undergo immunization or hard immunization.
One thing to keep in mind is that if a country has both the opportunity and the capacity to bring its entire population under the immunization program, that would be the best decision. No matter how much we try to limit the spread of a viral infection, we should be concerned about just spreading the virus among individuals.
When viral organisms become infected in the host body and try to reproduce there, they undergo various changes in their external or internal structure in any adverse condition. This is called ‘mutation’ in genetic engineering. In some cases, these mutated viruses may be much more deadly than previous viruses, and the vaccine or antidote discovered against the previous virus may not play an effective role in prevention. This matter has to be considered carefully.