Vaccine: Common Concerns

Many parents and caregivers have concerns about vaccines — some worry vaccines will harm their child, others aren't sure their child needs all the vaccines being given, and confusing information online and on social media doesn't help. But the risks associated with the vaccines children receive are much, much less than the risks associated with the diseases themselves.

Do vaccines really work?

Yes. Vaccine-preventable diseases have declined in every country with a successful vaccination programme — when vaccination rates are high, disease rates are low, and when rates drop (from fear of vaccines, or disrupted health care during a war or disaster), disease and related deaths always go up. Vaccines protect immunised children and the people close to them — like newborns too young to be vaccinated, or people whose immune systems don't work as well — by preventing the spread of disease.

Can vaccines wear out my child's immune system?

No. Our immune system responds to very large numbers of antigens found all around us every day — vaccines add only a few antigens to those numbers.

Are vaccines properly tested for safety?

Yes. Like all medicines, vaccines go through many steps before health authorities approve them, proving they're safe and effective at preventing the diseases they target. Once in use, health authorities continue monitoring for side effects, and serious side effects remain very rare.

Do vaccines have side effects?

The chance of getting sick from a vaccine-preventable disease is far greater than the very small risk of a serious vaccine side effect. Some children have mild pain, redness or a bit of swelling where the needle went in — acetaminophen can help. A mild fever is common after vaccination, and a high fever can happen in young infants, especially after a first dose; in a few cases fever can cause a febrile seizure, which is not dangerous and causes no brain damage, though it happens more often in children whose parents or siblings have also had them, or who already have epilepsy or a brain disorder. Fever with a rash may happen after MMR, MMRV or varicella vaccine, and anxiety about needles may cause fainting, especially in older children and teens. Other side effects, including serious allergic reactions, are very rare — children who've had a serious allergic reaction to a previous dose shouldn't get that vaccine again unless seen by a specialist or vaccinated in a special clinic equipped to manage severe reactions.

Can MMR cause autism or other developmental disorders?

No — there's no scientific evidence to support this. Because signs of autism can appear around the same age children receive MMR, some parents believe the vaccine causes it, and much of the controversy traces to a fraudulent 1998 paper that was later withdrawn. Many large studies worldwide have found no link between MMR — or any vaccine — and autism.

Can the pertussis vaccine cause brain damage, or SIDS?

No — but pertussis infection itself can cause seizures, brain damage and infant death. And no, many large studies have found no link between vaccines and SIDS — some studies actually found babies who died of SIDS were less likely to have been recently vaccinated than babies who didn't.

Can vaccines cause diabetes, asthma, allergies or cancer?

There's no relationship between vaccines and type 1 diabetes — while its cause isn't known, viral infections may be important triggers. Studies show vaccination doesn't increase asthma or other allergic disease. And there's no evidence of a link between vaccines and cancer — in fact, two vaccines protect against cancer: hepatitis B vaccine against liver cancer, and HPV vaccine against cervical and other genital cancers.

Can vaccines cause Crohn's disease, colitis or MS?

No association exists between vaccines and Crohn's disease or other inflammatory bowel disease. There's also no evidence vaccines cause MS or trigger flare-ups — hepatitis B and influenza vaccines specifically have been shown to have no effect on MS symptoms or progression, though seasonal flu infections themselves have been linked to MS flare-ups.

Can vaccines cause infections?

Most vaccines are inactivated and contain no living germs, so they can't cause infection. Live vaccines (mumps, rubella, chickenpox, rotavirus, nasal flu) contain weakened germs that don't cause disease in healthy people, though a few children get a very mild rash and fever with MMR, MMRV or varicella vaccine. Live vaccines may cause disease in people whose immune system doesn't work properly — these people should not receive them.