FAQ
Clear, evidence‑based answers to common questions about vaccines.
1) Why is there a new flu vaccine every year?
A new seasonal flu vaccine is needed every year because influenza viruses—especially Influenza A and Influenza B—constantly change (mutate).
Each year, scientists around the world, coordinated by the World Health Organization (WHO), monitor circulating flu strains and predict which ones are most likely to spread during the upcoming flu season. Based on these predictions, a new vaccine is developed to target those specific strains.
As a result, each year’s flu shot is designed to protect against different influenza viruses, rather than the same ones from the previous season.
3) Is natural immunity better than vaccine-acquired immunity?
Natural immunity can sometimes be strong, but it comes with much higher risks than vaccineacquired immunity. Getting immunity through infection means being exposed to the disease itself, which can cause serious complications.
For example, measles can lead to pneumonia, brain damage, or death, while the MMR vaccine has a very low risk of serious side effects and safely prevents infection. In some cases—such as with the Hib and tetanus vaccines—vaccines actually provide more reliable protection than natural infection.
5) Are vaccines safe?
Yes. Vaccines go through extensive safety testing before they are approved for use. This includes multiple stages of clinical trials to evaluate safety and effectiveness.
After approval, vaccines continue to be closely monitored to detect rare or unexpected side effects, ensuring ongoing safety for the public.
7) Isn’t there a danger of giving multiple vaccines and inducing an immunologic reaction that causes auto-immune disease?
No, vaccines do not induce autoimmune diseases. In reality, our bodies are introduced to many antigens simply through the activities of daily life. Antigens are particles—usually proteins—that vaccines use to stimulate the immune system. Most of these antigens are not injected into our bodies; they enter through small scratches and abrasions of the skin or mucosa, through breathing, and especially through eating or drinking.
Modern vaccines tend to be purified so that they contain the fewest antigens necessary to stimulate a protective immune response. Therefore, multiple vaccines do not overwhelm the immune system at all. We often give multiple vaccines at the same time
2) What is herd immunity? Is it real? Does it work?
Herd immunity, also known as community immunity, occurs when enough people in a community are vaccinated against a disease that it becomes difficult for the disease to spread.
This protects not only vaccinated individuals but also those who cannot be vaccinated — such as newborns or people with certain medical conditions — by reducing the risk of outbreaks.
4) Can vaccines cause the diseases they are designed to prevent?
No. This is a common myth, especially during flu season, when many respiratory illnesses are circulating at the same time. People may become sick after vaccination due to unrelated viruses, but not because of the vaccine itself.
In the case of influenza, neither the inactivated flu shot nor the live attenuated nasal spray vaccine can cause influenza. These vaccines are designed to safely stimulate the immune system without causing the disease.
6) Do vaccines contain harmful ingredients?
No. Vaccine ingredients are used in very small, carefully tested amounts to ensure safety and effectiveness. Substances such as thimerosal, formaldehyde, and aluminum are found naturally in the environment and in everyday foods, often at levels higher than those used in vaccines.
Extensive scientific research shows that these ingredients do not pose a health risk at the doses used in vaccines.