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Frequently Asked Questions

1. What are the different types of vaccines?

Different types of vaccines are:

  • Live attenuated vaccines use a weakened (or attenuated) form of the germ that causes a disease. Example – Mumps, Measles, Rubella (MMR) vaccine, Rotavirus vaccine, Chickenpox vaccine, Yellow fever vaccine.
  • Inactivated vaccines use the killed version of the germ that causes a disease. Example – Hepatitis A vaccine, Inactivated Flu vaccine, Inactivated polio vaccine (IPV), Rabies vaccine
  • Subunit, recombinant, polysaccharide, and conjugate vaccines use specific pieces of the germ — like its protein, sugar, or capsid (a casing around the germ). Example – Hepatitis B vaccine, Haemophilus Influenza type B (Hib) vaccine, Human Papilloma virus (HPV) vaccine
  • Toxoid vaccines use a toxin (harmful product) made by the germ that causes a disease. Example – Tetanus vaccine, Diphtheria vaccine
2. What are the constituents of a vaccine?

The main constituents of a  vaccine are:

  • Antigens are components derived from the disease causing organisms which are recognized as foreign by the immune system and elicit protective immune response to the vaccine.
  • Adjuvants improve the immune response to vaccine antigens and also reduce the dose of antigen needed. Adjuvants are mostly present in inactivated and subunit vaccines.
  • Stabilizers help the vaccine to maintain its effectiveness during storage. Example: lactose-sorbitol, sorbitol-gelatine
  • Preservatives are added to multi-dose vial vaccines to prevent bacterial and fungal growth. Example: Formaldehyde, thiomersal
  • Antibiotics are used in trace amounts during the manufacturing phase to prevent bacterial contamination of tissue culture cells. Only trace amounts of it appears in the final vaccine formulation.

Note: Some people might show intense reactions if they are sensitive to some of the components included in the vaccine.

3. Are vaccines safe?

Vaccines are safe. Every licensed vaccine  is rigorously tested for quality, efficacy and safety across multiple clinical trial phases before approval. Vaccines are also monitored on a regular basis by FDA, CDC, EMA and other federal agencies once they are in the market. The reactions induced by vaccines are in most of the cases mild.  Injection site reactions like pain, swelling and redness may occur. Systemic reactions can include headache, fatigue, fever, nausea. These mild reactions usually go away within a few days on their own. Serious adverse events are very rare.

4. Are vaccines safe for pregnant women? Which vaccines can pregnant women receive?
  • Not all but some vaccines are safe and are recommended during pregnancy to keep themselves and their babies healthy. The antibodies developed by the mothers in response to these vaccines not only protect them, but also cross the placenta and provide protection to their babies against serious illness in early life.
  • Vaccines recommended during pregnancy: Inactivated Flu vaccine, Tdap vaccine
  • Vaccines that are not recommended during pregnancy are HPV vaccine, MMR vaccine, Live influenza vaccine and varicella vaccine. In addition, vaccines like yellow fever vaccine, typhoid vaccine are also not recommended during pregnancy.
    (Note: In general Live-attenuated vaccines are not recommended during pregnancy)
5. Which vaccines can women of child bearing age receive?
  • Vaccines recommended for women of child bearing age are : MMR (Mumps, Measles and Rubella) vaccine, Influenza vaccine, Td/Tdap booster every ten years.
  • In addition following vaccines are also recommended for women of child bearing age at risk of diseases and who do not have a history of immunity
    • Hepatitis A, Hepatitis B, Human Papilloma Virus, Mumps, Measles, Rubella, meningococcal, Pneumococcal, Varicella (Chickenpox)
      Note: Women should avoid pregnancy until one month after receiving MMR vaccine.
6. Can breastfeeding women receive vaccines?

It is safe for a breastfeeding woman to receive vaccines. However, yellow fever vaccine is not recommended for breastfeeding women unless travel to yellow fever endemic countries is unavoidable. In this circumstance, consultation with the healthcare worker is recommended.

7. Does the adjuvant used in vaccines elicit intense anaphylactic reactions?

The adjuvants (if present) are present in very minor quantity in the vaccine composition. The vaccines containing adjuvants, just as other vaccines, are rigorously tested for quality, safety and efficacy in clinical trials before they are licensed and are continuously monitored after approval. Adjuvanted vaccines can cause more local reactions (such as redness, swelling, and pain at the injection site) and more systemic reactions (such as fever, chills and body aches) than non-adjuvanted vaccines. However, it is less likely that the adjuvants elicits intense anaphylactic reactions.

8. Do vaccines contain mercuric substances like thiomersal? If yes, are they harmful to human health?

Not all but many vaccines contain thiomersal which is used as a preservative to prevent bacterial or fungal growth. It is especially used in multi-dose vials. It has been in use since 1930 and no harmful effects have been reported except some minor reactions like redness and swelling at the injection site. There is no evidence of toxicity when exposed to thiomersal in vaccines.

9. Do vaccines contain pork content?

Gelatine, used as stabilizer in some vaccines, is usually derived from pigs. It is necessary to understand that the raw materials undergo massive transformation during the manufacturing process and the final product is different from the raw material.

10. Can a child receive multiple vaccines at a time?

A child can receive multiple vaccines at a time. Scientific evidence shows that several vaccines given at the same time has no negative effect on the child’s immune system. Children are exposed to several hundreds of foreign substances on a daily basis during normal activities like eating and playing.

The key advantage of receiving multiple vaccines at once is fewer clinic visits which saves both time and money.

11. Is it safe to administer combined vaccines to infants?

It is completely safe to administer combined vaccines to infants. There is no scientific evidence of severe adverse reactions caused due to combined vaccines. Several combined vaccines such as MMR vaccine, DPT vaccine are used for infant Immunisation. These vaccines are also regularly monitored to ensure their safety.

The combined vaccine will result in fewer injections and reduces discomfort for the child.

12. Is there a link between MMR vaccine and autism?

There is no evidence of any link between MMR vaccine and autism. This has been demonstrated by several studies conducted among large populations.

It is very important to share only credible scientific information on vaccine and vaccination.

13. With whom can I discuss about vaccine safety?

You can discuss about vaccine safety with your doctors or healthcare workers who are involved in vaccination. When you look for vaccine safety information, always browse information from trustworthy sources like WHO, UNICEF, CDC, Ministry of Health websites. In addition, always check the source of the information before reading or sharing with others.

14. Is it beneficial to vaccinate against a disease which no longer prevails in the society?
  • Although most of the vaccine-preventable diseases are not common anymore in many countries, the infectious agents causing these diseases are still circulating in some parts of the world. Effective vaccination has resulted that these diseases remain below the threshold of outbreak. But as soon as the vaccination coverage drops significantly, these diseases make their way back in our society. The measles outbreak of 2019 in many countries was due to drop in the vaccination coverage.
  • Two key reasons to get vaccinated are to protect ourselves and to protect those around us. Cooperation of every individual is required for a successful vaccination programme which ultimately ensures a disease free society.
15. Can vaccines cause the disease it is supposed to prevent?

Vaccines protect us against infectious diseases and there is no scientific evidence that illustrates vaccine cause disease that it supposed to prevent. Vaccines undergo several tests during the clinical trials to ensure their safety and efficacy and are also monitored on regular basis after licensing.


16. Do vaccines provide better immunity than natural infections?

Vaccines provide immunity similar to that of natural infections but they neither cause the disease nor put the immunised person at risk of serious complications. The price paid to get immunity through natural infection is very high and can lead to severe impairments and even death in some cases.


Further Readings

  1. World Health Organization. Vaccine Safety Basics Learning Manual. Geneva: World Health Organization; 2013.
  2. Center for Disease Control and Prevention. Vaccine Safety: Common Vaccine Safety questions and concerns. [Date Accessed: 29 May 2020]
Last updated: Jun 4, 2021
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