Basic reproduction number

A very important number for describing whether a disease can become an epidemic or not is R₀, pronounced "R naught" or "R zero". It refers to how many people a person who has this disease is expected to infect on average if there are no people immune to the disease. It is an abbreviation for basic reproduction number.

If R₀ > 1, a disease can become an epidemic. If R₀ < 1, it cannot. Most commonly known diseases have R₀ > 1. However, vaccines can be used to make enough people immune in a population to stop epidemics from happening. We can also use other measures to make the effective reproduction rate (R_e, usually written R_t with t for time) lower than the basic reproduction rate (R₀).

An example of a vaccine that works really well is the smallpox vaccine, which stopped smallpox virus from spreading so well that it no longer exists except in laboratories. Examples of making the effective reproduction rate lower than the basic reproduction rate are using condoms to stop sexually transmitted diseases from spreading or not getting close to others (physical distancing, often called social distancing) to stop respiratory diseases from spreading.

• SIR model

1. ↑ Guerra FM, Bolotin S, Lim G, Heffernan J, Deeks SL, Li Y, Crowcroft NS (December 2017). "The basic reproduction number (R₀) of measles: a systematic review". The Lancet. Infectious Diseases. 17 (12): e420 – e428. doi:10.1016/S1473-3099(17)30307-9. PMID 28757186.
2. ↑ Delamater PL, Street EJ, Leslie TF, Yang YT, Jacobsen KH (January 2019). "Complexity of the Basic Reproduction Number (R₀)". Emerging Infectious Diseases. 25 (1): 1–4. doi:10.3201/eid2501.171901. PMC 6302597. PMID 30560777.
3. ↑ Ireland's Health Services. Health Care Worker Information (PDF). Retrieved 2020-03-27.
4. ↑ McMorrow, Meredith (July 29, 2021). "Improving communications around vaccine breakthrough and vaccine effectiveness". p. 15. Archived from the original on January 25, 2022. Retrieved July 30, 2021.
5. ↑ Centers for Disease Control and Prevention; World Health Organization (2001). "History and epidemiology of global smallpox eradication". Smallpox: disease, prevention, and intervention (training course) (Presentation). Atlanta: Centers for Disease Control and Prevention (published 2014-08-25). cdc:27929. Archived (PDF) from the original on 2017-03-17. Retrieved 2021-06-17.
6. ↑ Fine, Paul E. M. (1993). "Herd Immunity: History, Theory, Practice". Epidemiologic Reviews. 15 (2): 265–302. doi:10.1093/oxfordjournals.epirev.a036121. PMID 8174658.
7. ↑ Luman, ET; Barker, LE; Simpson, DM; Rodewald, LE; Szilagyi, PG; Zhao, Z (May 2001). "National, state, and urban-area vaccination-coverage levels among children aged 19–35 months, United States, 1999". American Journal of Preventive Medicine. 20 (4): 88–153. doi:10.1016/s0749-3797(01)00274-4. PMID 12174806.
8. ↑ Jiles, RB; Fuchs, C; Klevens, RM (22 September 2000). "Vaccination coverage among children enrolled in Head Start programs or day care facilities or entering school". Morbidity and Mortality Weekly Report. 49 (9): 27–38. PMID 11016876.
9. ↑ Kretzschmar M, Teunis PF, Pebody RG (June 2010). "Incidence and reproduction numbers of pertussis: estimates from serological and social contact data in five European countries". PLOS Medicine. 7 (6): e1000291. doi:10.1371/journal.pmed.1000291. PMC 2889930. PMID 20585374.
10. ↑ Gani R, Leach S (December 2001). "Transmission potential of smallpox in contemporary populations". Nature. 414 (6865): 748–51. Bibcode:2001Natur.414..748G. doi:10.1038/414748a. PMID 11742399. S2CID 52799168. Retrieved 18 March 2020.
11. ↑ "Playing the Numbers Game: R0". National Emerging Special Pathogen Training and Education Center. Archived from the original on 12 May 2020. Retrieved 27 December 2020. [...] while infections that require sexual contact like HIV have a lower R₀ (2-5).
12. ↑ Billah, Arif; Miah, Mamun; Khan, Nuruzzaman (11 November 2020). "Reproductive number of coronavirus: A systematic review and meta-analysis based on global level evidence". PLOS ONE. 15 (11): e0242128. Bibcode:2020PLoSO..1542128B. doi:10.1371/journal.pone.0242128. PMC 7657547. PMID 33175914.
13. ↑ Freeman C. "Magic formula that will determine whether Ebola is beaten". The Telegraph. Telegraph.Co.Uk. Retrieved 30 March 2020.
14. ↑ Fraser C, Donnelly CA, Cauchemez S, Hanage WP, Van Kerkhove MD, Hollingsworth TD, et al. (June 2009). "Pandemic potential of a strain of influenza A (H1N1): early findings". Science. 324 (5934): 1557–61. Bibcode:2009Sci...324.1557F. doi:10.1126/science.1176062. PMC 3735127. PMID 19433588.
15. ↑ Chowell G, Miller MA, Viboud C (June 2008). "Seasonal influenza in the United States, France, and Australia: transmission and prospects for control". Epidemiology and Infection. 136 (6). Cambridge University Press: 852–64. doi:10.1017/S0950268807009144. PMC 2680121. PMID 17634159. The reproduction number across influenza seasons and countries lied in the range 0.9–2.0 with an overall mean of 1.3, and 95% confidence interval (CI) 1.2–1.4.