Too many vaccines at once overload a baby's immune system

What the research found

Trials have tested vaccines given together. A 2012 randomised trial in toddlers found a meningococcal vaccine given with the measles, mumps, rubella and varicella vaccine did not change the immune response to either. A 1992 randomised trial found hepatitis B, BCG and polio vaccines given together worked as well as when given separately, with no increase in adverse reactions.

A 1991 controlled trial in 111 infants gave hepatitis B vaccine alongside diphtheria-tetanus and oral polio vaccines. Reactions were almost absent, with mild pain in four infants. The response to the other vaccines was similar to babies who did not get the extra one. A 2014 systematic review of nine studies in adolescents also found HPV vaccine worked well and was acceptable when given with other vaccines.

A 2002 review in Pediatrics looked at the worry directly. It found infants can respond to vaccines, vaccinated children are not more likely to get other infections, and babies meet fewer antigens in vaccines today than 40 or 100 years ago. Australian guidance says babies' immune systems are very strong. US guidance says a healthy baby fights off thousands of germs every day, and vaccines carry only a tiny fraction of that load.

What it doesn’t mean

• One study found that oral polio vaccine given with BCG at birth was linked to a weaker skin-test response to BCG. That is a change between two specific vaccines. It does not show the immune system becoming overloaded.
• Spreading vaccines out is not safer. US guidance says delaying brings no known benefit and leaves babies unprotected when they are most at risk of serious disease.
• Tell the doctor or nurse if your child has a fever of 38.5 °C or more, a condition or treatment that lowers immunity, or has reacted badly to a vaccine before. Talk to your GP or child health nurse if you are worried about a reaction.