Editing Herd immunity (section)

===Protection of those without immunity===
[[File:WHO EN Herd Immunity Illustration 02 8Dec2020.png|thumb|Herd immunity protects vulnerable communities.]]
Some individuals either cannot develop immunity after vaccination or for medical reasons cannot be vaccinated.<ref name=pmid23910028>{{cite journal|vauthors=Munoz FM|title=Maternal immunization: an update for pediatricians|journal=Pediatric Annals|volume=42|issue=8|pages=153–8|date=August 2013|pmid=23910028|doi=10.3928/00904481-20130723-09}}</ref><ref name="ofg">{{cite web |title=Herd Immunity |url=http://vk.ovg.ox.ac.uk/herd-immunity |url-status=live |archive-url=https://web.archive.org/web/20190802220355/http://vk.ovg.ox.ac.uk/herd-immunity |archive-date=2 August 2019 |access-date=12 December 2017 |publisher=Oxford Vaccine Group, University of Oxford}}</ref><ref name=pmid24868544>{{cite journal|vauthors=Cesaro S, Giacchino M, Fioredda F, Barone A, Battisti L, Bezzio S, Frenos S, De Santis R, Livadiotti S, Marinello S, Zanazzo AG, Caselli D|display-authors=6|title=Guidelines on vaccinations in paediatric haematology and oncology patients|journal=BioMed Research International|volume=2014|pages=707691|date=2014|pmid=24868544|pmc=4020520|doi=10.1155/2014/707691|doi-access=free}}</ref> Newborn infants are too young to receive many vaccines, either for safety reasons or because [[passive immunity]] renders the vaccine ineffective.<ref name=pmid21293327>{{cite journal|title=General recommendations on immunization --- recommendations of the Advisory Committee on Immunization Practices (ACIP)|journal=MMWR. Recommendations and Reports|volume=60|issue=2|pages=1–64|date=January 2011|pmid=21293327|author1=National Center for Immunization Respiratory Diseases}}</ref> Individuals who are immunodeficient due to [[HIV/AIDS]], [[lymphoma]], [[leukemia]], [[bone marrow]] cancer, an impaired [[spleen]], [[chemotherapy]], or [[Radiation therapy|radiotherapy]] may have lost any immunity that they previously had and vaccines may not be of any use for them because of their immunodeficiency.<ref name=ofg/><ref name=pmid24868544/><ref name=pmid21293327/><ref name=pmid22773718>{{cite journal|vauthors=Wolfe RM|title=Update on adult immunizations|journal=Journal of the American Board of Family Medicine|volume=25|issue=4|pages=496–510|year=2012|pmid=22773718|doi=10.3122/jabfm.2012.04.100274|doi-access=free}}</ref>

A portion of those vaccinated may not develop long-term immunity.<ref name=pmid21427399/><ref>{{cite journal|vauthors=Esposito S, Bosis S, Morlacchi L, Baggi E, Sabatini C, Principi N|title=Can infants be protected by means of maternal vaccination?|journal=Clinical Microbiology and Infection|volume=18|issue=Suppl 5|pages=85–92|date=October 2012|pmid=22862749|doi=10.1111/j.1469-0691.2012.03936.x|doi-access=free}}</ref><ref name=rakel2>{{cite book|vauthors=Rakel D, Rakel RE|year=2015|title=Textbook of Family Medicine|url=https://books.google.com/books?id=8huMBgAAQBAJ&pg=PA99|publisher=Elsevier Health Sciences|pages=99, 187|isbn=978-0323313087|access-date=30 March 2015|archive-date=1 May 2021|archive-url=https://web.archive.org/web/20210501052904/https://books.google.com/books?id=8huMBgAAQBAJ&pg=PA99|url-status=live}}</ref> Vaccine [[contraindications]] may prevent certain individuals from being vaccinated.<ref name=pmid24868544/> In addition to not being immune, individuals in one of these groups may be at a greater risk of developing complications from infection because of their medical status, but they may still be protected if a large enough percentage of the population is immune.<ref name=ofg/><ref name=pmid24868544/><ref name=rakel2/><ref name=tulvar>{{cite book|vauthors=Tulchinsky TH, Varavikova EA|year=2014|title=The New Public Health: An Introduction for the 21st Century|url=https://books.google.com/books?id=2hg2IxB9WngC&pg=PA163|publisher=Academic Press|pages=163–82|isbn=978-0124157675|access-date=30 March 2015|archive-date=1 May 2021|archive-url=https://web.archive.org/web/20210501053021/https://books.google.com/books?id=2hg2IxB9WngC&pg=PA163|url-status=live}}</ref>

High levels of immunity in one age group can create herd immunity for other age groups.<ref name=pmid21604922/> Vaccinating adults against [[pertussis]] reduces pertussis incidence in infants too young to be vaccinated, who are at the greatest risk of complications from the disease.<ref name=pmid25560446>{{cite journal|vauthors=McGirr A, Fisman DN|title=Duration of pertussis immunity after DTaP immunization: a meta-analysis|journal=Pediatrics|volume=135|issue=2|pages=331–43|date=February 2015|pmid=25560446|doi=10.1542/peds.2014-1729|url=http://pdfs.semanticscholar.org/b2d8/0ba442e2834148d6f98b49b18bd5808e1348.pdf|archive-url=https://web.archive.org/web/20190303090923/http://pdfs.semanticscholar.org/b2d8/0ba442e2834148d6f98b49b18bd5808e1348.pdf|url-status=dead|archive-date=2019-03-03|s2cid=8273985}}</ref><ref>{{cite journal|vauthors=Zepp F, Heininger U, Mertsola J, Bernatowska E, Guiso N, Roord J, Tozzi AE, Van Damme P|display-authors=6|title=Rationale for pertussis booster vaccination throughout life in Europe|journal=The Lancet. Infectious Diseases|volume=11|issue=7|pages=557–70|date=July 2011|pmid=21600850|doi=10.1016/S1473-3099(11)70007-X }}</ref> This is especially important for close family members, who account for most of the transmissions to young infants.<ref name=pmid21604922/><ref name=rakel2/> In the same manner, children receiving vaccines against pneumococcus reduces pneumococcal disease incidence among younger, unvaccinated siblings.<ref name=pmid22862432>{{cite journal|vauthors=Pittet LF, Posfay-Barbe KM|title=Pneumococcal vaccines for children: a global public health priority|journal=Clinical Microbiology and Infection|volume=18|issue=Suppl 5|pages=25–36|date=October 2012|pmid=22862432|doi=10.1111/j.1469-0691.2012.03938.x|doi-access=free}}</ref> Vaccinating children against pneumococcus and rotavirus has had the effect of reducing [[Streptococcus pneumoniae|pneumococcus]]- and [[rotavirus]]-attributable hospitalizations for older children and adults, who do not normally receive these vaccines.<ref name=pmid22862432/><ref>{{cite journal|vauthors=Nakagomi O, Iturriza-Gomara M, Nakagomi T, Cunliffe NA|title=Incorporation of a rotavirus vaccine into the national immunisation schedule in the United Kingdom: a review|journal=Expert Opinion on Biological Therapy|volume=13|issue=11|pages=1613–21|date=November 2013|pmid=24088009|doi=10.1517/14712598.2013.840285|s2cid=5405583}}</ref><ref>{{cite journal|vauthors=Lopman BA, Payne DC, Tate JE, Patel MM, Cortese MM, Parashar UD|title=Post-licensure experience with rotavirus vaccination in high and middle income countries; 2006 to 2011|journal=Current Opinion in Virology|volume=2|issue=4|pages=434–42|date=August 2012|pmid=22749491|doi=10.1016/j.coviro.2012.05.002|url=https://zenodo.org/record/1258865|access-date=5 July 2019|archive-date=16 October 2019|archive-url=https://web.archive.org/web/20191016205411/https://zenodo.org/record/1258865|url-status=live}}</ref> [[Influenza]] (flu) is more severe in the elderly than in younger age groups, but [[influenza vaccine]]s lack effectiveness in this demographic due to a waning of the immune system with age.<ref name=pmid21604922/><ref name=pmid25003085>{{cite journal|vauthors=Kim TH|title=Seasonal influenza and vaccine herd effect|journal=Clinical and Experimental Vaccine Research|volume=3|issue=2|pages=128–32|date=July 2014|pmid=25003085|pmc=4083064|doi=10.7774/cevr.2014.3.2.128}}</ref> The prioritization of school-age children for seasonal flu immunization, which is more effective than vaccinating the elderly, however, has been shown to create a certain degree of protection for the elderly.<ref name=pmid21604922/><ref name=pmid25003085/>

For [[sexually transmitted infection]]s (STIs), high levels of immunity in heterosexuals of one sex induces herd immunity for heterosexuals of both sexes.<ref name="pmid15627236">{{cite journal |vauthors=Garnett GP |date=February 2005 |title=Role of herd immunity in determining the effect of vaccines against sexually transmitted disease |journal=The Journal of Infectious Diseases |volume=191 |issue=Suppl 1 |pages=S97-106 |doi=10.1086/425271 |pmid=15627236 |doi-access=free}}</ref><ref name=pmid22219162>{{cite journal|vauthors=Lowy DR, Schiller JT|title=Reducing HPV-associated cancer globally|journal=Cancer Prevention Research|volume=5|issue=1|pages=18–23|date=January 2012|pmid=22219162|pmc=3285475|doi=10.1158/1940-6207.CAPR-11-0542}}</ref><ref name=pmid23391351>{{cite journal|vauthors=Lenzi A, Mirone V, Gentile V, Bartoletti R, Ficarra V, Foresta C, Mariani L, Mazzoli S, Parisi SG, Perino A, Picardo M, Zotti CM|display-authors=6|title=Rome Consensus Conference - statement; human papilloma virus diseases in males|journal=BMC Public Health|volume=13|pages=117|date=February 2013|pmid=23391351|pmc=3642007|doi=10.1186/1471-2458-13-117|doi-access=free}}</ref> Vaccines against STIs that are targeted at heterosexuals of one sex result in significant declines in STIs in heterosexuals of both sexes if vaccine uptake in the target sex is high.<ref name=pmid22219162/><ref name=pmid23391351/><ref name=pmid21962468>{{cite journal|vauthors=Garland SM, Skinner SR, Brotherton JM|title=Adolescent and young adult HPV vaccination in Australia: achievements and challenges|journal=Preventive Medicine|volume=53|issue=Suppl 1|pages=S29-35|date=October 2011|pmid=21962468|doi=10.1016/j.ypmed.2011.08.015}}</ref> Herd immunity from female vaccination does not, however, extend to males who have sex with males.<ref name=pmid23391351/> High-risk behaviors make eliminating STIs difficult because, even though most infections occur among individuals with moderate risk, the majority of transmissions occur because of individuals who engage in high-risk behaviors.<ref name=pmid15627236/> For this reason, in certain populations it may be necessary to immunize high-risk individuals regardless of sex.<ref name=pmid15627236/><ref name=pmid23391351/>