Arming the Immune System

Vaccines outlook

In 1796, English physician Edward Jenner introduced the rst BUILDING COVERAGE SAVING LIVES vaccine, for smallpox, when he infected a young boy with cowpox. Vaccines initially developed in the 1950s and 1960s, such as those for polio and measles, are commonly Case numbers of certain infectious diseases in the administered globally. Those introduced more recently, such as that for rotavirus, are less widely used. United States dropped precipitously after e¡ective In the years since, vaccines — a name derived from the Latin word vaccines for each were widely adopted. ARMING THE for cow — have been developed for many diseases, saving millions Global vaccine coverage in 2018 Polio of lives. But the ght to conquer infectious disease continues. Measles first-dose (MCV1) 60 Polio (Pol3) Hepatitis B (HepB3) By Neil Savage; infographic by Alisdair Macdonald 40 Inactivated polio IMMUNE SYSTEM Haemophilus influenzae type B (Hib3) vaccine was The WHO recommends Measles second-dose (MCV2) two doses of measles 20 introduced in 1955. 1. Antigens, often in the 2. Antigen-presenting 3. APCs move to where 4a. Naive killer 5a. If the vaccine Rubella (RCV1) vaccine, but 23 of its IMMUNE form of molecules on cells (APCs) capture immune cells cluster. They T cells become contains a live 194 member states Pneumococcal diseases (PCV3) STIMULATION the surface of viruses and ingest the activate T helper cells, active killer T cells attenuated virus that require only one dose. 0 or bacteria, are antigen, then display which trigger activity in specific to the infects cells, killer Rotaviruses (RotaC) 1950 1955 2017 Vaccines can be administered introduced into the pieces of it on their killer T cells (4a) and the antigen. T cells will then target orally, nasally or by injection: 0 10 20 30 40 50 60 70 80 90 100 bloodstream. surfaces. maturation of B cells (4b). and destroy those cells. into the muscle mass, into the Estimated vaccine coverage (%) Measles layer between skin and muscle 800 or into the outer layer of skin. They stimulate an immune Memory killer T cell 600 response that gives the body Antigens 400 the ability to mount a swifter THE LUXURY OF HESITANCY defence to the same pathogen Although 79% of people globally think that vaccines are safe, trust varies widely between nations. Europe has 4a 5a 200 if it is encountered again. T helper cell some of the lowest levels of perceived safety — a finding that might partly explain the surge in measles cases seen in Ukraine in 2018. But other factors besides hesitancy to vaccinate also a¡ect the spread of infections. 0 Share of people who think vaccines are safe in 2018 (%) 1950 1963 2017 In 2016, only 31% of 6-year-olds Killer Memory cells had received a second measles T cell 30–39 40–49 50–59 60–69 70–79 80–89 90–100 No data If the vaccinated person jab in Ukraine. Mumps 1 2 3 encounters the pathogen 200 again, memory cells enable the body to mount a faster, 150 stronger defence. Plasma B cell 100

Virus 50 4b 5b 0 Antigen-presenting France experienced a 1967 2017 cell (APC) 462% increase in measles cases between Memory B cell 2017 and 2018. Rubella Bacterium 60 4b. Naive B cells, activated either by T helper cells 5b. Plasma B cells produce antibodies that bind to or directly by antigens, become plasma B cells antigens, preventing them from entering cells and specific to the antigen. marking them for destruction by killer T cells. 40

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53,218 20 Increase in measles cases 2017–18 23,558 0 Inactivated vaccine Subunit vaccine Live, attenuated Toxoid vaccine IN DEVELOPMENT 2017 2018 20,758 VACCINE 13,622 1966 1969 2017 vaccine 10,362 VARIETIES 4,978 5,076 5,160 5,668 DNA vaccine 2,913 There are several Hepatitis B types of vaccine in DNA from pathogens, 60 use, each with their sometimes attached to own strengths and another virus or France Sudan Serbia Thailand Venezuela Brazil Yemen Philippines Madagascar Ukraine 40 weaknesses. Many bacterium, is used to are administered generate an immune along with adjuvants response. 20 — substances such In human trials for LONG ROAD TO NEW VACCINES as aluminium salts, herpesvirus, influenza 0 lipids and RNA that and Zika virus. Development programmes are under way for a number of deadly diseases that currently lack a vaccine. 1966 1986 2017 strengthen the In many cases, the pathogen responsible was identified decades ago, but e¡ective vaccination strategies The pathogen is One or more parts of A virus is weakened, immune response. A toxin produced by have proved elusive. treated with heat or the pathogen, such as often by repeatedly the pathogen, Hepatitis A chemicals to kill it a protein, are isolated passing it through a instead of the Recombinant 60 before it is introduced and used to evoke an tissue culture in which pathogen itself, is vector vaccine Schistosome into the body. immune response. it replicates poorly. deactivated and Live but harmless Malaria* ~1.5 40  Easy to store and  Low risk of adverse  Activates killer T cells. used to produce the viruses are genetically Leishmania immune response. transport. reaction.  One or two doses engineered to express HIV MILLION  Low risk of causing  Can be used in can provide lifelong  Unable to cause an antigen to a 20 an infection. people with weakened immunity. disease or to spread. dangerous virus, which 0 15 30 45 60 75 90 105 120 135 150 165 180 deaths from these immune systems. the immune system Number of years since pathogen was identified four diseases in 2016.  Elicits weaker  Must be refrigerated.  Stable, so easy to 0 immune response.  Can be di¡icult to distribute. can target.  Less safe for people *A pilot study of a malaria vaccine began in three countries in 2019. 1966 1995 2017  May require manufacture. with weakened immune  May require Being explored for several doses and  May require systems. boosters to maintain Zika virus, HIV and boosters. boosters. immunity. Ebola. Examples: measles, SOURCES: Immune stimulation: WHO/CDC/www.historyofvaccines.org; Vaccine varieties: US Dept. Health & Human Services/www.historyofvaccines.org; Building coverage: WHO; Examples: polio, Examples: hepatitis B, mumps, rubella, Examples: The luxury of hesitancy: Gallup Wellcome Global Monitor 2018 (Wellcome, 2019); Long road to new vaccines: S. Vanderslott & M. Roser https://ourworldindata.org/vaccination (2019)/WHO; hepatitis A, rabies influenza, pertussis varicella, rotavirus diphtheria, tetanus Saving lives: S. W. Roush et al. J. Am. Med. Assoc. 298, 2155–2163 (2007)/CDC.

Nature publications remain neutral with regard to contested jurisdictional claims in published maps. US cases (thousands) Reported