Editing Vaccine (section)

==Effectiveness==
<!--This section is linked from [[Mumps]].-->
[[File:RougeoleDP.jpg|thumb|A child with [[measles]], a vaccine-preventable disease<ref>{{cite web| url=https://www.cdc.gov/measles/vaccination.html| title=Measles Vaccination CDC| date=5 February 2018| access-date=13 November 2018| archive-date=19 November 2019| archive-url=https://web.archive.org/web/20191119142614/https://www.cdc.gov/measles/vaccination.html| url-status=live}}</ref>]]

There is overwhelming scientific consensus that vaccines are a very safe and effective way to fight and eradicate infectious diseases.<ref>{{cite journal | vauthors = Orenstein WA, Bernier RH, Dondero TJ, Hinman AR, Marks JS, Bart KJ, Sirotkin B | title = Field evaluation of vaccine efficacy | journal = Bulletin of the World Health Organization | volume = 63 | issue = 6 | pages = 1055–1068 | date = 1985 | pmid = 3879673 | pmc = 2536484 }}</ref><ref>{{cite web|url=https://hub.jhu.edu/2017/01/11/vaccines-autism-public-health-expert/|title=The science is clear: Vaccines are safe, effective, and do not cause autism|date=11 January 2017|website=The Hub|access-date=16 April 2019|archive-date=28 September 2017|archive-url=https://web.archive.org/web/20170928005601/https://hub.jhu.edu/2017/01/11/vaccines-autism-public-health-expert/|url-status=live}}</ref><ref>{{cite journal | vauthors = Ellenberg SS, Chen RT | title = The complicated task of monitoring vaccine safety | journal = Public Health Reports | volume = 112 | issue = 1 | pages = 10–20; discussion 21 | date = 1997 | pmid = 9018282 | pmc = 1381831 }}</ref><ref>{{cite web|url=http://www.healthychildren.org/English/safety-prevention/immunizations/Pages/Vaccine-Safety-The-Facts.aspx|title=Vaccine Safety: The Facts|website=HealthyChildren.org|date=10 October 2018 |access-date=16 April 2019|archive-date=16 April 2019|archive-url=https://web.archive.org/web/20190416034623/https://www.healthychildren.org/English/safety-prevention/immunizations/Pages/Vaccine-Safety-The-Facts.aspx|url-status=live}}</ref> The [[immune system]] recognizes vaccine agents as foreign, destroys them, and "remembers" them. When the [[virulence|virulent]] version of an agent is encountered, the body recognizes the protein coat on the agent, and thus is prepared to respond, by first neutralizing the target agent before it can enter cells, and secondly by recognizing and destroying infected cells before that agent can multiply to vast numbers.<ref name="Mak">{{cite book |last1=Mak |first1=Tak W. |last2=Saunders |first2=Mary E. |last3=Jett |first3=Bradley D. |title=Primer to The immune response |date=2014 |publisher=Academic Cell |location=Burlington, MA |isbn=978-0-12-385245-8 |pages=3–20 |edition=2nd |chapter-url=https://www.sciencedirect.com/science/article/pii/B9780123852458000017 |access-date=18 April 2022 |chapter=Chapter 1 – Introduction to the Immune Response |archive-date=18 April 2022 |archive-url=https://web.archive.org/web/20220418192756/https://www.sciencedirect.com/science/article/pii/B9780123852458000017 |url-status=live }}</ref><ref name="Clem">{{cite journal |last1=Clem |first1=Angela S |title=Fundamentals of Vaccine Immunology |journal=Journal of Global Infectious Diseases |date=2011 |volume=3 |issue=1 |pages=73–78 |doi=10.4103/0974-777X.77299 |pmid=21572612 |pmc=3068582 |issn=0974-777X |doi-access=free }}</ref>

In 1958, there were 763,094 cases of measles in the United States; 552 deaths resulted.<ref name="pmid15106120">{{cite journal |vauthors=Orenstein WA, Papania MJ, Wharton ME |date=May 2004 |title=Measles elimination in the United States |journal=The Journal of Infectious Diseases |volume=189 |issue=Suppl 1 |pages=S1–3 |doi=10.1086/377693 |pmid=15106120 |doi-access=free}}</ref><ref name="pmid18463608">{{cite journal |vauthors=<!--staff--> |date=May 2008 |title=Measles – United States, January 1 – April 25, 2008 |url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5718a5.htm |url-status=live |journal=MMWR. Morbidity and Mortality Weekly Report |volume=57 |issue=18 |pages=494–498 |pmid=18463608 |archive-url=https://web.archive.org/web/20171011235122/https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5718a5.htm |archive-date=11 October 2017}}</ref> After the introduction of new vaccines, the number of cases dropped to fewer than 150 per year (median of 56).<ref name="pmid18463608" /> In early 2008, there were 64 suspected cases of measles. Fifty-four of those infections were associated with importation from another country, although only thirteen percent were actually acquired outside the United States; 63 of the 64 individuals either had never been vaccinated against measles or were uncertain whether they had been vaccinated.<ref name="pmid18463608" />

The measles vaccine is estimated to prevent a million deaths every year.<ref name="sullivan2005">{{cite news |last=Sullivan |first=Patricia |name-list-style=vanc |date=13 April 2005 |title=Maurice R. Hilleman dies; created vaccines |url=https://www.washingtonpost.com/wp-dyn/articles/A48244-2005Apr12.html |url-status=live |archive-url=https://web.archive.org/web/20121020102622/http://www.washingtonpost.com/wp-dyn/articles/A48244-2005Apr12.html |archive-date=20 October 2012 |access-date=9 January 2014 |work=Wash. Post}}</ref>

Vaccines led to the eradication of [[smallpox]], one of the most contagious and deadly diseases in humans.<ref>{{cite web |title=Smallpox |url=https://www.who.int/csr/disease/smallpox/en/ |url-status=live |archive-url=https://web.archive.org/web/20070922184729/http://www.who.int/csr/disease/smallpox/en/ |archive-date=22 September 2007 |access-date=16 April 2019 |publisher=[[World Health Organization]] (WHO)}}</ref> Other diseases such as rubella, [[poliomyelitis|polio]], measles, mumps, [[chickenpox]], and [[typhoid fever|typhoid]] are nowhere near as common as they were a hundred years ago thanks to widespread vaccination programs. As long as the vast majority of people are vaccinated, it is much more difficult for an outbreak of disease to occur, let alone spread. This effect is called [[herd immunity]]. Polio, which is transmitted only among humans, is targeted by an extensive [[Poliomyelitis eradication|eradication campaign]] that has seen endemic polio restricted to only parts of three countries (Afghanistan, Nigeria, and Pakistan).<ref name="eradication1">{{cite web |date=27 March 2014 |title=WHO South-East Asia Region certified polio-free |url=http://www.searo.who.int/mediacentre/releases/2014/pr1569/en/ |archive-url=https://web.archive.org/web/20140327235218/http://www.searo.who.int/mediacentre/releases/2014/pr1569/en/ |archive-date=27 March 2014 |access-date=3 November 2014 |publisher=WHO}}</ref> However, the difficulty of reaching all children, cultural misunderstandings, and [[disinformation]] have caused the anticipated eradication date to be missed several times.<ref>{{cite web |date=21 May 2021 |title=Statement following the Twenty-Eighth IHR Emergency Committee for Polio |url=https://www.who.int/news/item/21-05-2021-statement-following-the-twenty-eighth-ihr-emergency-committee-for-polio |url-status=live |archive-url=https://web.archive.org/web/20220419014821/https://www.who.int/news/item/21-05-2021-statement-following-the-twenty-eighth-ihr-emergency-committee-for-polio |archive-date=19 April 2022 |access-date=19 April 2022 |website=[[World Health Organization]] (WHO)}}</ref><ref>{{cite journal |last1=Grassly |first1=Nicholas C. |date=5 August 2013 |title=The final stages of the global eradication of poliomyelitis |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |volume=368 |issue=1623 |page=20120140 |doi=10.1098/rstb.2012.0140 |issn=0962-8436 |pmc=3720038 |pmid=23798688}}</ref><ref>{{cite journal |last1=Ittefaq |first1=Muhammad |last2=Abwao |first2=Mauryne |last3=Rafique |first3=Shanawer |date=3 August 2021 |title=Polio vaccine misinformation on social media: turning point in the fight against polio eradication in Pakistan |journal=Human Vaccines & Immunotherapeutics |volume=17 |issue=8 |pages=2575–2577 |doi=10.1080/21645515.2021.1894897 |issn=2164-554X |pmc=8475597 |pmid=33705246}}</ref><ref>{{cite news |date=24 January 2022 |title=Disinformation disturbs anti-polio drives |url=https://tribune.com.pk/story/2340158/disinformation-disturbs-anti-polio-drives |url-status=live |archive-url=https://web.archive.org/web/20220510052846/https://tribune.com.pk/story/2340158/disinformation-disturbs-anti-polio-drives |archive-date=10 May 2022 |access-date=19 April 2022 |work=The Express Tribune}}</ref>

Vaccines also help prevent the development of antibiotic resistance. For example, by greatly reducing the incidence of pneumonia caused by ''[[Streptococcus pneumoniae]]'', vaccine programs have greatly reduced the prevalence of infections resistant to penicillin or other first-line antibiotics.<ref>{{cite journal |last1=Abbott |first1=Alison |date=19 July 2017 |title=19 July 2017 ''Vaccines promoted as key to stamping out drug-resistant microbes'' "Immunization can stop resistant infections before they get started, say scientists from industry and academia." |url=https://www.nature.com/articles/d41586-017-01711-6 |journal=Nature |doi=10.1038/d41586-017-01711-6 |archive-url=https://web.archive.org/web/20170722121157/http://www.nature.com/articles/d41586-017-01711-6 |archive-date=22 July 2017}}</ref>

=== Limitations ===
Limitations to their effectiveness, nevertheless, exist.<ref name="pmid19393917">{{cite journal | vauthors = Grammatikos AP, Mantadakis E, Falagas ME | title = Meta-analyses on pediatric infections and vaccines | journal = Infectious Disease Clinics of North America | volume = 23 | issue = 2 | pages = 431–457 | date = June 2009 | pmid = 19393917 | doi = 10.1016/j.idc.2009.01.008 }}</ref> Sometimes, protection fails for vaccine-related reasons such as failures in vaccine attenuation, vaccination regimens or administration.<ref name="wied"/>

Failure may also occur for host-related reasons if the host's immune system does not respond adequately or at all. Host-related lack of response occurs in an estimated 2-10% of individuals, due to factors including genetics, immune status, age, health and nutritional status.<ref name="wied"/> One type of [[primary immunodeficiency]] disorder resulting in genetic failure is [[X-linked agammaglobulinemia]], in which the absence of an enzyme essential for [[B cell]] development prevents the host's immune system from generating [[Antibody|antibodies]] to a [[pathogen]].<ref>{{cite book |last1=Justiz Vaillant |first1=AA |last2=Ramphul |first2=K |title=Antibody Deficiency Disorder |location=Treasure Island, FL |publisher=StatPearls Publishing |date=January 2022 |pmid=29939682 |url=https://www.ncbi.nlm.nih.gov/books/NBK507905/ |access-date=18 April 2022}}</ref><ref name="Reda">{{cite journal |last1=Reda |first1=Shereen M. |last2=Cant |first2=Andrew J. |title=The importance of vaccination and immunoglobulin treatment for patients with primary immunodeficiency diseases (PIDs) – World PI Week April 22–29, 2015: FORUM |journal=European Journal of Immunology |date=May 2015 |volume=45 |issue=5 |pages=1285–1286 |doi=10.1002/eji.201570054 |pmid=25952627 |s2cid=1922332 }}</ref>

Host–pathogen interactions and responses to infection are dynamic processes involving multiple pathways in the immune system.<ref name="Jo">{{cite journal |last1=Jo |first1=Eun-Kyeong |title=Interplay between host and pathogen: immune defense and beyond |journal=Experimental & Molecular Medicine |date=December 2019 |volume=51 |issue=12 |pages=1–3 |doi=10.1038/s12276-019-0281-8 |pmid=31827066 |pmc=6906370 |issn=2092-6413}}</ref><ref name="Janeway">{{cite journal |last1=Janeway |first1=Charles A Jr. |last2=Travers |first2=Paul |last3=Walport |first3=Mark |last4=Shlomchik |first4=Mark J. |title=The Humoral Immune Response |journal=Immunobiology: The Immune System in Health and Disease|edition=5th |date=2001 |url=https://www.ncbi.nlm.nih.gov/books/NBK10752/ |access-date=18 April 2022 |archive-date=2 January 2021 |archive-url=https://web.archive.org/web/20210102142711/https://www.ncbi.nlm.nih.gov/books/NBK10752/ |url-status=live }}</ref> A host does not develop antibodies instantaneously: while the body's [[innate immunity]] may be activated in as little as twelve hours, [[adaptive immunity]] can take 1–2 weeks to fully develop. During that time, the host can still become infected.<ref>{{cite book |last1=Grubbs |first1=Hailey |last2=Kahwaji |first2=Chadi I. |title=Physiology, Active Immunity |location=Treasure Island, FL |publisher=StatPearls Publishing |date=January 2022 |pmid=29939682 |url=https://www.ncbi.nlm.nih.gov/books/NBK513280/ |access-date=18 April 2022 |archive-date=12 November 2021 |archive-url=https://web.archive.org/web/20211112145718/https://www.ncbi.nlm.nih.gov/books/NBK513280/ |url-status=live }}</ref>

Once antibodies are produced, they may promote immunity in any of several ways, depending on the class of antibodies involved. Their success in clearing or inactivating a pathogen will depend on the amount of antibodies produced and on the extent to which those antibodies are effective at countering the strain of the pathogen involved, since different strains may be differently susceptible to a given immune reaction.<ref name="Janeway"/> 
In some cases vaccines may result in partial immune protection (in which immunity is less than 100% effective but still reduces risk of infection) or in temporary immune protection (in which immunity wanes over time) rather than full or permanent immunity. They can still raise the reinfection threshold for the population as a whole and make a substantial impact.<ref name="Gomes">{{cite journal |last1=Gomes |first1=M. Gabriela M. |last2=White |first2=Lisa J. |last3=Medley |first3=Graham F. |title=Infection, reinfection, and vaccination under suboptimal immune protection: epidemiological perspectives |journal=Journal of Theoretical Biology |date=21 June 2004 |volume=228 |issue=4 |pages=539–549 |doi=10.1016/j.jtbi.2004.02.015 |pmid=15178201 |bibcode=2004JThBi.228..539G |hdl=10400.7/53 |hdl-access=free |issn=0022-5193}}</ref> They can also mitigate the severity of infection, resulting in a lower [[mortality rate]], lower [[morbidity]], faster recovery from illness, and a wide range of other effects.<ref name="Bonanni">{{cite journal |last1=Bonanni |first1=Paolo |last2=Picazo |first2=Juan José |last3=Rémy |first3=Vanessa |title=The intangible benefits of vaccination – what is the true economic value of vaccination? |journal=Journal of Market Access & Health Policy |date=12 August 2015 |volume=3 |pages=10.3402/jmahp.v3.26964 |doi=10.3402/jmahp.v3.26964 |pmid=27123182 |pmc=4802696 |issn=2001-6689}}</ref><ref name="Stanciu">{{cite book |last1=Stanciu |first1=Stefan G. |title=Micro and Nanotechnologies for Biotechnology |year= 2016 |publisher=BoD – Books on Demand |isbn=978-953-51-2530-3 |url=https://books.google.com/books?id=h3eQDwAAQBAJ&pg=PA88 |access-date=19 April 2022 |archive-date=14 January 2023 |archive-url=https://web.archive.org/web/20230114091817/https://books.google.com/books?id=h3eQDwAAQBAJ&pg=PA88 |url-status=live }}</ref>

Those who are older often display less of a response than those who are younger, a pattern known as [[Immunosenescence]].<ref name="Frasca">{{cite journal |last1=Frasca |first1=Daniela |last2=Diaz |first2=Alain |last3=Romero |first3=Maria |last4=Garcia |first4=Denisse |last5=Blomberg |first5=Bonnie B. |title=B Cell Immunosenescence |journal=Annual Review of Cell and Developmental Biology |date=6 October 2020 |volume=36 |issue=1 |pages=551–574 |doi=10.1146/annurev-cellbio-011620-034148 |pmid=33021823 |pmc=8060858 |issn=1081-0706}}</ref>
[[Immunologic adjuvant|Adjuvants]] commonly are used to boost immune response, particularly for older people whose immune response to a simple vaccine may have weakened.<ref name="neighmond2010">{{cite news | url=https://www.npr.org/templates/story/story.php?storyId=123406640 | title=Adapting Vaccines For Our Aging Immune Systems | date=7 February 2010 | work=Morning Edition | publisher=NPR | access-date=9 January 2014 | last=Neighmond | first=Patti | name-list-style = vanc | url-status=live | archive-url=https://web.archive.org/web/20131216191614/http://www.npr.org/templates/story/story.php?storyId=123406640 | archive-date=16 December 2013}}</ref>

The [[vaccine efficacy|efficacy]] or performance of the vaccine is dependent on several factors:
* the disease itself (for some diseases vaccination performs better than for others)
* the strain of vaccine (some vaccines are specific to, or at least most effective against, particular strains of the disease)<ref name="pmid10435956">{{cite journal | vauthors = Schlegel M, Osterwalder JJ, Galeazzi RL, Vernazza PL | title = Comparative efficacy of three mumps vaccines during disease outbreak in Eastern Switzerland: cohort study | journal = BMJ | volume = 319 | issue = 7206 | page = 352 | date = August 1999 | pmid = 10435956 | pmc = 32261 | doi = 10.1136/bmj.319.7206.352 }}</ref>
* whether the [[vaccination schedule]] has been properly observed.
* idiosyncratic response to vaccination; some individuals are "non-responders" to certain vaccines, meaning that they do not generate antibodies even after being vaccinated correctly.
* assorted factors such as ethnicity, age, or genetic predisposition.

If a vaccinated individual does develop the disease vaccinated against ([[breakthrough infection]]), the disease is likely to be less severe and less transmissible than in unvaccinated cases.<ref name="pmid12955637">{{cite journal | vauthors = Préziosi MP, Halloran ME | title = Effects of pertussis vaccination on disease: vaccine efficacy in reducing clinical severity | journal = Clinical Infectious Diseases | volume = 37 | issue = 6 | pages = 772–779 | date = September 2003 | pmid = 12955637 | doi = 10.1086/377270 | doi-access = free }}</ref><ref>{{Cite journal |last1=Connell |first1=Anna R. |last2=Connell |first2=Jeff |last3=Leahy |first3=T. Ronan |last4=Hassan |first4=Jaythoon |date=2020-09-18 |title=Mumps Outbreaks in Vaccinated Populations – Is It Time to Re-assess the Clinical Efficacy of Vaccines? |journal=Frontiers in Immunology |language=English |volume=11 |page=2089 |doi=10.3389/fimmu.2020.02089 |doi-access=free |issn=1664-3224 |pmc=7531022 |pmid=33072071}}</ref>

Important considerations in an effective vaccination program:<ref>{{Cite journal|last1=Miller|first1=E.|last2=Beverley|first2=P. C. L.|last3=Salisbury|first3=D. M.|date=1 July 2002|title=Vaccine programmes and policies|journal=British Medical Bulletin|volume=62|issue=1|pages=201–211|doi=10.1093/bmb/62.1.201|pmid=12176861|issn=0007-1420|doi-access=free}}</ref>
# careful modeling to anticipate the effect that an immunization campaign will have on the epidemiology of the disease in the medium to long term
# ongoing surveillance for the relevant disease following introduction of a new vaccine
# maintenance of high immunization rates, even when a disease has become rare