A friend recognizes value in vaccinating in general - against major diseases - but with a caveat that they are opposed to the flu vaccine specifically.

They claim that vaccines weaken the immune system, and reasoned that (in conjunction with the fact that flu vaccines may only offer ~40% (random example) efficacy against some strains, some given flu season) this weakening of the immune system actually increases occurrence and/or chance of illness.

Is it true that vaccines "weaken the immune system" ?
Whether flu vaccines specifically, or vaccines in general.

I tried Googling this, but most results pertain to vaccination for those who are already immunocompromised ?

One source writes :

Is there any evidence that vaccines do cause illness and immune system dysfunction?

One answer came in a careful study of illness patterns observed in babies before and after vaccination, published in Clinical Pediatrics in 1988. If vaccines cause a weakened immune system, then we would expect to see a higher incidence of illness following vaccination. In that study conducted in Israel, the incidence of acute illnesses in the 30 day period following DTP vaccine was compared to the incidence in the same children for the 30 day period prior to vaccine. The three-day period immediately following vaccine was excluded because children frequently develop fever as a direct response to vaccine toxins. A total of 82 healthy infants received DTP, and their symptoms were reported by parents and observed by a pediatrician at weekly intervals. Those babies experienced a dramatic increase in fever, diarrhea, and cough in the month following DTP vaccine compared to their health before the shot.


But that article's subsequent anti-vaccine extremism makes me disregard that claim, without significant research towards proper debunking of its source, if it exists.

Are there any legitimate studies that support / oppose the notion that vaccination weakens the immune system in otherwise healthy people ?

  • 2
    Thank you for asking such a rational question about vaccines.
    – Carey Gregory
    Jun 23, 2018 at 5:03
  • Don't you just hate it when articles such as the one linked here mention published studies without providing references? This is a good question which in a way is challenging this. Jun 24, 2018 at 8:41
  • Just a few observations: exactly what does "babies" mean? IOW, what age were the subjects? "...reported by parents," isn't exactly the most scientific method for determining outcome. And the parents observational bias could easily have influenced the pediatricians conclusions. We also don't know if the reported symptoms were caused by something other than the vaccine, e.g. diet, environmental conditions. Not exactly a controlled study.
    – BillDOe
    Jun 25, 2018 at 0:26
  • I think this might be the study that my quoted source referred to : ncbi.nlm.nih.gov/pubmed/3262480
    – robut
    Jun 25, 2018 at 12:15
  • Applying simple reasoning you can imagine that the weakening effect is only temporary, until your immune system have adapted to start creating antigens to the vaccinated disease(s) in question. Once that period is over, your immune system will be stronger in the sense that it can handle some more diseases. That's why you probably don't want to vaccinate against other diseases while in the middle of a pandemic or other out-break, unrelated to what you're getting vaccinated against.
    – not2qubit
    Mar 26, 2020 at 20:23

1 Answer 1


I have found a couple of papers which debunk this myth. The links here go directly to free PDF copies and there are DOI links in the references in case the PDF links die.

The most recent paper I can find at the moment is by Hilton, et al. (2006).

The recent controversy surrounding the safety of the measles, mumps, and rubella vaccine (MMR) has heightened parents’ concerns about the safety of vaccines, and led some to believe that giving vaccines in a combined form may ‘overload’ children's immune systems. However, to date no studies have been published examining how British parents conceptualise the notion of ‘immune-overload’ or how they relate this concept to their own children. Eighteen focus groups were conducted with parents between November 2002 and March 2003. [....] We conclude that although there is no scientific evidence that supports parents’ fears about combined vaccines causing ‘immune-overload’, policy makers need to recognise these concerns if they are to successfully persuade parents that combined vaccines are safe.

There is also Offit, et al. (2002).

Recent surveys found that an increasing number of parents are concerned that infants receive too many vaccines. Implicit in this concern is that the infant’s immune system is inadequately developed to handle vaccines safely or that multiple vaccines may overwhelm the immune system. In this review, we will examine the following: 1) the ontogeny of the active immune response and the ability of neonates and young infants to respond to vaccines; 2) the theoretic capacity of an infant’s immune system; 3) data that demonstrate that mild or moderate illness does not interfere with an infant’s ability to generate protective immune responses to vaccines; 4) how infants respond to vaccines given in combination compared with the same vaccines given separately; 5) data showing that vaccinated children are not more likely to develop infections with other pathogens than unvaccinated children; and 6) the fact that infants actually encounter fewer antigens in vaccines today than they did 40 or 100 years ago.

In summary, they said

Current studies do not support the hypothesis that multiple vaccines overwhelm, weaken, or “use up” the immune system. On the contrary, young infants have an enormous capacity to respond to multiple vaccines, as well as to the many other challenges present in the environment. By providing protection against a number of bacterial and viral pathogens, vaccines prevent the “weakening” of the immune system and consequent secondary bacterial infections occasionally caused by natural infection.


Hilton, S., Petticrew, M., & Hunt, K. (2006). Combined vaccines are like a sudden onslaught to the body's immune system’: parental concerns about vaccine ‘overload’ and ‘immune-vulnerability’. Vaccine, 24(20), 4321-4327.
DOI: 10.1016/j.vaccine.2006.03.003
PDF: http://www.academia.edu/download/43189354/Combined_vaccines_are_like_a_sudden_ons20160229-3560-1cbx2wu.pdf

Offit, P. A., Quarles, J., Gerber, M. A., Hackett, C. J., Marcuse, E. K., Kollman, T. R., ... & Landry, S. (2002). Addressing parents’ concerns: do multiple vaccines overwhelm or weaken the infant’s immune system?. Pediatrics, 109(1), 124-129.
DOI: 10.1542/peds.109.1.124
PDF: http://pediatrics.aappublications.org/content/109/1/124.full-text.pdf

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