Vaccines: concerns, questions and false claims
Information from the European Medicines Agency (EMA) addressing concerns, questions and false claims about vaccines.
Human
Vaccines
Every year, vaccines save millions of lives around the world. They are one of the most effective tools we have to prevent serious infectious diseases.
Vaccines help protect people from serious and potentially deadly diseases, and they can also help reduce or stop a disease from spreading in the community. This in turn protects vulnerable people such as babies, the elderly and people with a weakened immune system.
Before any vaccine is approved for use, it undergoes rigorous testing to ensure its safety and effectiveness. Even after approval, vaccines continue to be closely monitored for side effects.
Like any medicine, vaccines can cause side effects in some people, but these are typically mild and short-lived.
For information about COVID-19 vaccines, see COVID-19 vaccines key facts.
Concerns, questions and false claims
Vaccines do not cause autism. The false belief that they do originates from a widely discredited study published in 1998.
This study claimed a link between the measles-mumps-rubella (MMR) vaccine and autism. However, the study contained falsified data, and it was subsequently retracted by the journal where it was published.
Despite all the accumulated evidence showing no link between vaccines and autism, the falsified study still generates controversy and confusion despite being retracted.
Rigorous studies have consistently found no evidence of a link between vaccines and autism. A review of these studies is available in the Annual Review of Virology (see reference below).
These studies include ecological studies in the United Kingdom, the United States, Japan and Canada, none of which found a correlation between autism and measles vaccination coverage.
Ecological studies are a type of research that compares groups or populations to find relationships between exposure and health outcomes.
In addition, case-control studies, which compared measles vaccination histories of children with and without autism, have been conducted in the United Kingdom, the United States, Poland and Japan. No increased risk of autism following measles vaccination with either MMR vaccine or monovalent measles vaccine was found in these studies.
Cohort studies have also been conducted in various countries. For instance, a Danish study used healthcare registries of more than 500,000 children born in Denmark between 1991 and 1998. This study identified no association between MMR vaccination and autism. A cohort study is a type of study that follows a group of individuals (a ‘cohort’) with shared characteristics over time to determine how certain exposures are associated with health outcomes.
References
Review
DeStefano F, Shimabukuro TT. The MMR Vaccine and Autism. Annu Rev Virol. 2019 Sep 29;6(1):585-600. doi: 10.1146/annurev-virology-092818-015515. Epub 2019 Apr 15. PMID: 30986133; PMCID: PMC6768751
Ecological studies
Kaye JA, Melero-Montes MdM, Jick H. Mumps, measles, and rubella vaccine and the incidence of autism recorded by general practitioners: a time trend analysis. BMJ. 2001;322(7284):460–3.
Dales L, Hammer SJ, Smith NJ. Time trends in autism and MMR immunization coverage in California. JAMA. 2001;285(9):1183–5.
Honda H, Shimizu Y, Rutter M. No effect of MMR withdrawal on the incidence of autism: a total population study. J Child Psychol Psychiatry. 2005;46(6):572–9.
Fombonne E, Zakarian R, Bennett A, Meng L, McLean-Heywood D. Pervasive developmental disorders in Montreal, Quebec, Canada: prevalence and links with immunizations. Pediatrics. 2006;118(1):e139–5.
Case-control studies
Smeeth L, Cook C, Fombonne E, Heavey L, Rodrigues LC, Smith PG, Hall AJ. MMR vaccination and pervasive developmental disorders: a case-control study. Lancet. 2004 Sep 11-17;364(9438):963-9. doi: 10.1016/S0140-6736(04)17020-7. PMID: 15364187
DeStefano F, Bhasin TK, Thompson WW, Yeargin-Allsopp M, Boyle C. Age at first measles-mumps-rubella vaccination in children with autism and school-matched control subjects: a population-based study in metropolitan Atlanta. Pediatrics. 2004 Feb;113(2):259-66. doi: 10.1542/peds.113.2.259. PMID: 14754936
Mrozek-Budzyn D, Kiełtyka A, Majewska R. Lack of association between measles-mumps-rubella vaccination and autism in children: a case-control study. Pediatr Infect Dis J. 2010 May;29(5):397-400. doi: 10.1097/INF.0b013e3181c40a8a. PMID: 19952979
Uno Y, Uchiyama T, Kurosawa M, Aleksic B, Ozaki N. The combined measles, mumps, and rubella vaccines and the total number of vaccines are not associated with development of autism spectrum disorder: the first case-control study in Asia. Vaccine. 2012 Jun 13;30(28):4292-8. doi: 10.1016/j.vaccine.2012.01.093. Epub 2012 Apr 20. PMID: 22521285
Cohort study
Madsen KM, Hviid A, Vestergaard M, Schendel D, Wohlfahrt J, Thorsen P, Olsen J, Melbye M. A population-based study of measles, mumps, and rubella vaccination and autism. N Engl J Med. 2002 Nov 7;347(19):1477-82. doi: 10.1056/NEJMoa021134. PMID: 12421889
A few vaccines contain a mercury-containing compound called thiomersal (also known as thimerosal).
Thiomersal has been used as a preservative in vaccines for decades. There is no evidence of harm from thiomersal in vaccines and no association between vaccination with thiomersal-containing vaccines and specific neurodevelopmental disorders.
The main risk from thiomersal is the potential for allergic reactions.
In line with a global goal of reducing environmental exposure to mercury, the presence of thiomersal in vaccines has almost disappeared over recent years.
For example, among the vaccines centrally authorised in the EU, only the multidose vial formulations of pandemic preparedness influenza vaccines contain very low amounts of thiomersal to avoid contamination during repeated use. These vaccines are not on the market as they can only be used during an influenza pandemic.
Immunisation with vaccines, including those that may contain thiomersal, continues to offer great health benefits to the population that far outweigh the risks of side effects.
References
Adjuvants are ingredients used in a vaccine to help create a stronger immune response. They are an essential part of vaccines, and many vaccines would not work as well without them.
All the ingredients of a vaccine are clearly listed in the product information.
Adjuvants are used in very small amounts. There is no evidence that adjuvants are harmful in such small amounts. Some adjuvants such as aluminium have been used safely since the 1930s and their safety profile is well known.
Newer compounds used as adjuvants are always tested first in pre-clinical studies for their safety, at much higher doses than those used in a vaccine.
The vaccine with adjuvant is then tested in clinical trials to see how safe it is and how well it works.
Vaccine developers also carry out tests to see if the vaccine works without an adjuvant and will use the smallest amount of adjuvant needed for a strong immune response.
Levels of adjuvants are carefully controlled to ensure they are safe.
Adjuvanted vaccines lead to local reactions (such as redness, swelling, and pain at the injection site) and systemic reactions (such as fever, chills and body aches) more often than non-adjuvanted vaccines. These reactions are temporary and usually disappear within days.