Herd Immunity to Ebolaviruses is not a Realistic Target for Current Vaccination Strategies

Abstract

22The recent West African Ebola virus pandemic, which affected >28,000 individuals increased 23 interest in anti-Ebolavirus vaccination programs. Here, we systematically analyzed the 24 requirements for a prophylactic vaccination program based on the basic reproductive number 25 (R0, i.e. the number of secondary cases that result from an individual infection). Published R0 26 values were determined by a systematic literature research and ranged from 0.37 to 20. R0s 27 ≥4 realistically reflected the critical early outbreak phases and superspreading events. Based 28 on the R0, the herd immunity threshold (Ic) was calculated using the equation Ic=1-(1/R0). 29The critical vaccination coverage (Vc) needed to provide herd immunity was determined by 30 including the vaccine effectiveness (E) using the equation Vc=Ic/E. At an R0 of 4, the Ic is 31 75% and at an E of 90%, more than 80% of a population need to be vaccinated to establish 32 herd immunity. Such vaccination rates are currently unrealistic because of resistance against 33 vaccinations, financial/ logistical challenges, and a lack of vaccines that provide long-term 34 protection against all human-pathogenic Ebolaviruses. Hence, outbreak management will for 35 the foreseeable future depend on surveillance and case isolation. Clinical vaccine candidates 36 are only available for Ebola viruses. Their use will need to be focused on health care workers, 37 potentially in combination with ring vaccination approaches. 38 39

Application of a fast and cost-effective ‘three-in-one’ MMR ELISA as a tool for surveying anti-MMR humoral immunity: the Hungarian experience

“…In the literature, R 0 and HIT values are generally estimated as follows: R 0 Measles = 12–18, HIT Measles = 92–95%, R 0Mumps = 4–12, HIT Mumps = 75–86%, R 0Rubella = 5–7, HIT Rubella = 83–86% [35]. Often used models for population-level estimation are the HIT ( I c ); I c = 1 − (1/ R 0 ), and the critical vaccination coverage ( V c ); V c = I c / E , where E is vaccine effectiveness [34–37]. Despite the remarkable theoretical knowledge, public health practice aims at 100% coverage, with all the doses recommended, bearing in mind that – because of the diversity of individual immune responses – 100% is never achievable.…”

“…the critical vaccination coverage (V c ); V c = I c /E, where E is vaccine effectiveness [34][35][36][37]. Despite the remarkable theoretical knowledge, public health practice aims at 100% coverage, with all the doses recommended, bearing in mind thatbecause of the diversity of individual immune responses -100% is never achievable.…”

Herd Immunity: A Realistic Target?

“…To illustrate the problems of achieving herd immunity Masterson et al showed this is not a realistic target for current vaccination strategies, using Ebola outbreaks as an example [32]. They analysed the requirements for a prophylactic program based on the basic reproductive number R0.…”

A Comparative Study of Challenges and Strategic Management: Lessons Learned from SARS, MERS, HIV & Ebola Outbreaks

“…While there is a vaccine for diphtheria, measles, mumps, pertussis, polio, rubella, smallpox, and influenza, Ebola vaccines, although proven effective, are not being used due to questions on the effectiveness of the vaccine over a long period, and also the vaccination would be costly. Several patients who were tried to be vaccinated in West Africa during the Ebola outbreak refused to vaccinate [25] [26]. There is also no vaccine developed to date for the coronaviruses like SARS and MERS.…”