Herd immunity: How it keeps you safe
- Julian Heinonen
- Dec 25, 2025
- 3 min read
Have you ever had smallpox? It’s a highly contagious disease caused by a virus that killed an estimated 300 to 500 million people in the 20th century. If you were born in 1980 or later, you most likely haven’t had it. This is because, in 1980, the World Health Organization (WHO) declared smallpox eradicated. But how?
Population immunization is a public health strategy that protects communities from infectious diseases by using vaccines. The more people who are vaccinated, the higher the rate of immunity, making it harder for diseases to spread from person to person. This is also referred to as herd immunity, community immunity or mass immunization. The number of people who need to be vaccinated in order to achieve herd immunity varies, as some diseases are more contagious than others. This is called the herd immunity threshold.Â
Countries typically establish national vaccination programs that include routine vaccinations for babies and young children, as well as booster shots for adults and older people. A booster means an extra dose of a vaccine that helps maintain immunity. Vaccination programs may vary from one country to another, as different regions may need protection from different diseases.
Natural vs Artificial immunity - which is better?
When your body comes into contact with a virus or a bacteria, it begins producing special proteins called antibodies to neutralize the threat. Once the infection is over, memory cells have learned to recognize the chemical pattern of the invader and remain in your body to make sure it doesn’t cause illness again. This is called active immunity, and it can be achieved either through natural immunity or through artificial (vaccine-induced) immunity.Â
Natural immunity: Gained when you become infected and recovered from the disease.
Artificial immunity: gained through vaccination, which introduces a dead or weakened form of the virus or bacteria.
While natural immunity is good at preventing some diseases, we can’t rely on it alone because of the risks and uncertainties that come with serious illnesses. For example, it’s possible to acquire natural immunity to measles that will prevent you from getting it ever again, but it can also kill or cause serious complications. That’s not a good gamble. We also can’t predict who will survive and who won’t, since people’s overall health and living conditions differ a lot. Additionally, a person’s immune response and vulnerability to different infections vary at different stages of life.
Vaccines are a safer and faster way of gaining herd immunity. It’s easier to vaccinate a whole community, than wait for everyone to get infected and deal with the possible consequences.
Keeping others safe
Vaccination doesn’t just keep you safe, but also those who can’t get vaccinated. For example, people with certain medical conditions, those with weakened immune systems and pregnant people can’t get certain vaccines and rely on others to maintain the herd immunity to stay safe. You can think of herd immunity as a protective barrier for those who need it the most.Â
Some diseases caused by viruses can’t be treated with antibiotics or other medicines, so the only way to control them is by immunization. With strong and consistent immunization programs, we can lower the threat of such diseases.
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Assessed and Endorsed by the MedReport Medical Review Board