Skip directly to site content Skip directly to page options Skip directly to A-Z link Skip directly to A-Z link Skip directly to A-Z link
Volume 26, Number 4—April 2020
Conference Summary

Workshop Report on Global Harmonization of Enterovirus Vaccines

Tzu-Yu Weng, Hua Yen, Kutub Mahmood, Javier Martin, and Min-Shi LeeComments to Author 
Author affiliations: National Health Research Institutes, Zhunan, Taiwan (T.-Y. Weng, H. Yen, M.-S. Lee); Center for Vaccine Innovation and Access, PATH, Seattle, Washington, USA (K. Mahmood); National Institute for Biological Standard and Control, Potters Bar, UK (J. Martin)

Suggested citation for this article

The Asia-Pacific Network for Enterovirus Surveillance in the National Health Research Institutes hosted a workshop on May 2, 2019, to discuss the harmonization of 2 licensed enterovirus vaccines, poliovirus and enterovirus A71 (EV-A71), especially regarding the standardization of vaccine antigens (Appendix). Speakers from the UK National Institute for Biologic Standard and Control (NIBSC), US PATH, industries, and regulatory agencies shared their experiences.

Sabin strain–derived live-attenuated oral poliovirus vaccines (OPV) and wild strain–derived inactivated poliovirus vaccines (IPV) have been widely used. Since wild-type 2 poliovirus was eradicated, bivalent OPV (only type 1 and 3) replaced trivalent OPV. Wild-type 3 is almost eradicated, and major efforts are under way to eradicate type 1. In addition, wild strains are not feasible to produce conventional IPV (cIPV) after wild polioviruses are eradicated. Therefore, the World Health Organization (WHO) recommends the development of Sabin strain–derived IPV (sIPV) for the endgame plan of global poliovirus eradication programs. Because WHO international standard (IS) antigen for quantifying cIPV antigens could not be effectively used to quantify sIPV, new reagents based on sIPV need to be established.

Three EV-A71 vaccines have been licensed in China, and 2 EV-A71 vaccine candidates were evaluated in phase III trials in Taiwan. Experience with IPV indicates that establishing WHO IS antigens is critical for global harmonization of EV-A71 vaccines. Thus, NIBSC and the China National Institute of Food and Drug Control (NIFDC) coordinated an international study for the first IS antigen of EV-A71 vaccines. Some participants in the international study shared their results in the workshop. This report summarizes outcomes of presentations and discussion.

Global Development of sIPV

In 2018, global demand for IPV was ≈90 million doses, but only ≈70 million doses of IPV were delivered, suggesting a potential shortage of IPV. To mitigate the IPV shortage for vaccination campaigns (catch-up or outbreak responses), WHO recommended that a fractional dose (one fifth of full IPV dose) could be administered intradermally ( Regarding the global development of sIPV, 4 organizations have obtained marketing approval for sIPV, but D-antigen units of these 4 sIPV differ. Therefore, PATH is collaborating with WHO and NIBSC to develop standard antigens and antibody reagents to quantify D-antigen units of sIPV. According to the current WHO plan, IPV vaccination will continue for at least 10 years after poliovirus eradication. High-income countries will use combination vaccines containing IPV for a longer period.

Global Harmonization of sIPV

Potency of cIPV is evaluated using 2 methods: 1) in vitro ELISA to measure D-antigen unit and 2) in vivo rat immunogenicity to measure postvaccination serum neutralization antibody titers. For in vitro ELISA, an IS antigen for cIPV (IS 12/104) has been established but is not suitable for measuring D-antigen unit of sIPV. Consequently, NIBSC initiated the international collaboration study to establish the first IS of sIPV (1). It is essential to understand the correlation between in vitro and in vivo vaccine potencies for different sIPV products and ideally link both to results in human studies.

Global Harmonization of EV-A71 Vaccines

Three EV-A71 vaccines (genotype C4) were licensed in China, and these 3 vaccines have different dose units. Therefore, NIFDC, China established a national standard to harmonize the measurement of EV-A71 vaccine antigens (2). In Taiwan, 2 EV-A71 vaccine candidates (genotype B4) were evaluated in phase III trials, and doses of these 2 candidates were determined by quantifying total proteins. In 2015, NIBSC and NIFDC established the first IS for human EV-A71 antiserum for measuring serum neutralizing antibody titers (3). Likewise, on the basis of prior experiences with IPV, establishing potency assays of EV-A71 vaccines is pivotal for global harmonization, including in vitro ELISA for measuring D-antigen units and in vivo animal immunogenicity for measuring postvaccination serum neutralization antibody titers.

In Vitro ELISA for Measuring D-Antigen Units of Inactivated EV-A71 Vaccines

Four potential IS candidates (2 genotype C4 products from China and 2 genotype B4 products from Taiwan) were evaluated in an international collaboration study. NIBSC developed lyophilization protocols to optimize the stability of IS candidates and established an ELISA using mouse monoclonal antibody (CT11F9) as detection antibody and rabbit polyclonal antibody as capture antibody. Fourteen laboratories joined the international study, and most of them established in-house ELISA using different mouse monoclonal antibodies and rabbit polyclonal antibodies. EV-A71 vaccines contain both empty and full virus particles with different structural conformation (46), which is not the case for IPV products. Therefore, it may be necessary to understand the relative contribution of these 2 viral forms to the antigenic and immunogenic properties of different EV-A71 vaccines. Moreover, establishing the correlation between in vitro ELISA and in vivo animal immunogenicity for both full and empty EV-A71 virus particles is critical. The 2 different particles need to be obtained by purification and heat-treatment, which enables transition from full to empty virus particles. In addition, clarifying the necessity of establishing IS for different EV-A71 genotypes is important.

In Vivo Animal Immunogenicity

Mice, rats, and rabbits have been used to evaluate immunogenicity of inactivated EV-A71 vaccines, but standard protocols for these animal models have not been established. Previous studies have detected antigenic variations among EV-A71 genogroups A, B, and C and correlated cross-reactive antibody responses with EV-A71 infections in rabbits and children (7,8). Correlating cross-reactive antibody responses with EV-A71 vaccination in animals and children is desirable. Previous IPV studies had shown that rats were used to evaluate immunogenicity with multiple dose units (1, 0.5, 0.25, 0.125, and 0.0625 human dose units) (9,10). Therefore, similar animal studies should be conducted for inactivated EV-A71 vaccines.



We thank Ya-Yen Chen, Fang-Lin Kuo, and Wen-Chiung Chang for administrative support.

The workshop was funded by the National Health Research Institutes and Taiwan National Flagship Project (108-0324-01-19-11).



  1. Crawt  L, Atkinson  E, Tedcastle  A, Pegg  E, Minor  P, Cooper  G, et al. sIPV Study Group. Differences in antigenic structure of inactivated poliovaccines made from Sabin live-attenuated and wild-type poliovirus strains: impact on vaccine potency assays. J Infect Dis. 2019; (Feb):19.
  2. Liang  Z, Mao  Q, Gao  Q, Li  X, Dong  C, Yu  X, et al. Establishing China’s national standards of antigen content and neutralizing antibody responses for evaluation of enterovirus 71 (EV71) vaccines. Vaccine. 2011;29:966874. DOIPubMedGoogle Scholar
  3. Cooper  G, Mao  Q, Crawt  L, Wang  Y, Dougall  T, Rigsby  P, et al.; Collaborative Study Group. Establishment of the 1st WHO International Standard for anti-EV71 serum (human). Biologicals. 2018;53:3950. DOIPubMedGoogle Scholar
  4. Liu  CC, Guo  MS, Lin  FH, Hsiao  KN, Chang  KH, Chou  AH, et al. Purification and characterization of enterovirus 71 viral particles produced from vero cells grown in a serum-free microcarrier bioreactor system. PLoS One. 2011;6:e20005. DOIPubMedGoogle Scholar
  5. Wu  CY, Yu  SL, Chen  YT, Chen  YH, Hsiao  PW, Chow  YH, et al. The mature EV71 virion induced a broadly cross-neutralizing VP1 antibody against subtypes of the EV71 virus. PLoS One. 2019;14:e0210553. DOIPubMedGoogle Scholar
  6. Chia  MY, Chung  WY, Wang  CH, Chang  WH, Lee  MS. Development of a high-growth enterovirus 71 vaccine candidate inducing cross-reactive neutralizing antibody responses. Vaccine. 2018;36:116773. DOIPubMedGoogle Scholar
  7. Huang  M-L, Chiang  P-S, Chia  M-Y, Luo  S-T, Chang  L-Y, Lin  T-Y, et al. Cross-reactive neutralizing antibody responses to enterovirus 71 infections in young children: implications for vaccine development. PLoS Negl Trop Dis. 2013;7:e2067. DOIPubMedGoogle Scholar
  8. Chia  M-Y, Chung  W-Y, Chiang  P-S, Chien  Y-S, Ho  M-S, Lee  M-S. Monitoring antigenic variations of enterovirus 71: implications for virus surveillance and vaccine development. PLoS Negl Trop Dis. 2014;8:e3044. DOIPubMedGoogle Scholar
  9. Wood  D, Heath  A. Collaborative study for the establishment of a rat bioassay for inactivated poliomyelitis vaccine. Pharmeuropa Spec Issue Biol. 2000;2000–1:2549.
  10. Bevilacqua  JM, Young  L, Chiu  SW, Sparkes  JD, Kreeftenberg  JG. Rat immunogenicity assay of inactivated poliovirus. Dev Biol Stand. 1996;86:1217.PubMedGoogle Scholar


Suggested citation for this article: Weng TY, Yen H, Mahmood K, Martin J, Lee MS. Workshop report on global harmonization of enterovirus vaccines. Emerg Infect Dis. 2020 Apr [date cited].

DOI: 10.3201/eid2604.191273

Original Publication Date: March 09, 2020

Table of Contents – Volume 26, Number 4—April 2020

EID Search Options
presentation_01 Advanced Article Search – Search articles by author and/or keyword.
presentation_01 Articles by Country Search – Search articles by the topic country.
presentation_01 Article Type Search – Search articles by article type and issue.



Please use the form below to submit correspondence to the authors or contact them at the following address:

Min-Shi Lee, National Institute of Infectious Diseases and Vaccinology, National Health Research Institutes, 35 Keyan Rd., Zhunan, Miaoli County 35053, Taiwan

Send To

10000 character(s) remaining.


Page created: March 09, 2020
Page updated: March 09, 2020
Page reviewed: March 09, 2020
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.