What is this so-called herd immunity? Let's learn about it simply.

Have you heard the term "Herd Immunity" before? We've been hearing this term a lot, especially with the COVID-19 pandemic. Some people also call it "herd immunity." So have you ever wondered what it means in simple terms? Don't worry, even though this is a big scientific thing, let's talk about it very simply, in our language.

What is Herd Immunity?

Simply put, herd immunity is when a large portion of the population in a certain area has acquired immunity, that is, protection, against a certain disease.

Think about it this way. Most of the people in our village are immune to measles. So even if someone from outside comes into the village with measles, the chances of them spreading the disease to others are very low. Why? Because most of the people around them don't get the disease. It's like the virus that causes the disease runs out of ways to get there. After a while, the virus has nowhere to spread, so the disease gradually disappears from the community.

For example, this provides great protection for people like young babies, people with weakened immune systems (e.g., cancer patients, organ transplant recipients), and people who cannot get vaccinated because the chance of the disease coming to them is reduced.

How do we create this herd immunity?

There are two main ways this herd immunity can occur.

1. Natural Infection

When a person is infected with a virus or bacteria, our body's immune system starts to fight it. To fight this, our body makes something called antibodies . After the illness is cured, these antibodies remain in our body. If the same germ that caused the disease comes back to our body one day, our body uses those antibodies to defeat it. This is how the Zika virus outbreak in Brazil was controlled. Within two years, 63% of the population there had been infected with the virus, leading to herd immunity, researchers believe.

2. Through vaccination

Vaccinations are the safest and most effective way to build herd immunity. What a vaccine does is "trick" our bodies into thinking that we have the disease, without actually getting it. Our immune system then makes the antibodies we mentioned earlier. So if the germ that actually causes the disease ever enters our bodies, our bodies are ready to fight it. Polio was eradicated from countries like the United States because of the herd immunity created by vaccination.

Herd Immunity Threshold and R0 Value

Not every disease requires the same number of people to develop herd immunity. It depends on how quickly the disease spreads. A measure of this speed is called R0 (R-naught) .

R0 refers to the average number of people a person with the disease can infect in a society with no immunity. For the R0 value to increase, and for herd immunity to occur, the percentage of people with immunity in the society must also increase significantly.

Look at the table below, and this will become clearer to you.

COVID-19 and herd immunity: Why is this so difficult?

The biggest challenge when the COVID-19 pandemic began in 2019 was that it was a "new" or "novel" virus. This means that people had not been infected with this virus before. Therefore, no one in the entire world had any natural immunity against it.

Even though billions of COVID-19 vaccines have been administered worldwide, and millions have recovered from the disease, we still have not achieved herd immunity to COVID-19. There are several reasons for this.

• Mutations: The COVID-19 virus is constantly mutating. You may remember variants like Delta and Omicron . These new variants spread much faster than the original virus. This means that the R0 value increased. This also increased the percentage required for herd immunity. Also, these mutations can reduce the protection provided by the vaccine over time.

• Vaccine effectiveness and vaccination problems: While the COVID-19 vaccine has been very effective in preventing severe illness and death, not enough people have been vaccinated to achieve herd immunity. Some people have not had access to the vaccine, others have declined the vaccine for personal reasons. Also, not everyone has received the required doses and booster doses to achieve maximum protection from the vaccine.

So, what is the best way to stop the spread of disease in society?

When it comes to COVID-19, getting vaccinated and getting booster shots on time is the best way to protect yourself and your loved ones from serious illness.

There are many things we can do to prevent the spread of other infectious diseases:

• Get vaccinated on time for diseases for which there is a vaccine (e.g. measles, hepatitis A and B, influenza).
• Indoors, that is, indoors, if there are many people together, open the windows and ensure good ventilation.
• Wash your hands thoroughly with soap and water before eating, after using the bathroom, and frequently. If you don't have access to hand washing, use hand sanitizer.
• Always keep frequently touched surfaces (doorknobs, keyboards, remote controls) clean.
• Cover your mouth and nose with a tissue or your elbow when you cough or sneeze. This will prevent germs from getting on your hands.
• If you are feeling sick or have symptoms of a contagious disease, stay home. This will prevent you from spreading the disease to others.