Dear Colleagues,

Effective and safe vaccines against several infectious diseases have long been available worldwide, however the incidence of vaccine-preventable diseases (VPDs) has been rising in recent years, even in high-income countries with universal access to vaccines. Since 2008, the Global Health Program at the Council on Foreign Relations has tracked global outbreaks of measles, mumps, polio, rubella, pertussis, and other VPDs (i.e. diphtheria, varicella, meningitis, rotavirus).

The resurgence of VPDs is the result of several factors, including the anti-vaccine movement and vaccine hesitancy, the decreasing effectiveness of certain vaccines such as pertussis vaccine, and travel to countries where VPD rates are higher.

Although in the period 2000–2017, annual measles incidence and mortality rates decreased by 83% and 80%, respectively [1], the eradication of the disease has not yet been achieved. Measles outbreaks continue to occur both in Europe, because of suboptimal vaccination coverage, and in the USA by travelers returning from countries where the disease is still circulating.

The same applies to rubella and congenital rubella syndrome, which in April 2015 were declared as “eliminated” in the Americas region by the Pan-American Regional Office of the World Health Organization. However, as declared by the 29^th Pan American Sanitary Conference held in Washington, D.C. in September 2017, “maintaining the status in an increasingly interconnected world will be an ongoing challenge in the coming years because countries are constantly at risk of importing and reintroducing the viruses and thus undoing the progress they have made” [2].

In addition, pertussis is poorly controlled because vaccine effectiveness rapidly declines when the time since the last vaccination surpasses four years, and the risk of contracting the disease steadily increases in children only a few years after the completion of immunization [3]. Moreover, the United States and other developed countries have experienced a resurgence in mumps cases over the last decade, even in communities with high vaccine coverage, indicating a central role of waning immunity in large outbreaks [4-5].

Poliomyelitis is close to eradication, and so far only four countries (Afghanistan, India, Nigeria and Pakistan) have never completely interrupted the transmission of wild poliovirus. However, in November 2018, the 19^th IHR Emergency Committee convened to discuss the status of the international spread of poliovirus, and unanimously agreed that the risk of polio spread continues to be a public health emergency of international concern. The committee cautioned that failure to eradicate polio would lead to a global resurgence of the disease [6]. Indeed, until poliovirus transmission is interrupted, all countries remain at risk of virus importation, through population movement.

The diphtheria outbreak in Bangladesh and Yemen due to war, and the more recent outbreaks in Venezuela, Haiti and South Africa should raise concern that diphtheria remains a public health issue in 2017/2018 [7]. Although diphtheria toxoid vaccine was included in the Global Expanded Programme on Immunization, the recent re-emergence of diphtheria provides clear evidence of inadequate homogeneous population coverage.

Finally, we cannot forget that VPDs are unnecessarily costly at both the individual and societal levels. At the individual level they cause mostly severe cardiovascular, respiratory, or neurological complications with increased risk of hospitalization, and at the societal level an increase of costs.

Therefore, prevention strategies and control programs should be implemented and surveillance systems should be strengthened to respond to threat of the re-emergence of VPDs. In particular, the administration of booster vaccine doses should be prioritized.

In this Special Issue, we will present a set of papers assessing the risks of infectious disease due to the re-emergence of VPDs.

We look forward to your contributions.

Dr. Patrizio Pezzotti
Dr. Maria Cristina Rota
Dr. Stefania Bellino
Guest Editors

References

1. Dabbagh A, Laws RL, Steulet C, et al. Progress Toward Regional Measles Elimination — Worldwide, 2000–2017. MMWR Morb Mortal Wkly Rep 2018; 67:1323–1329. DOI: http://0-dx-doi-org.brum.beds.ac.uk/10.15585/mmwr.mm6747a6
2. https://www.paho.org/hq/index.php?option=com_docman&view=download&category_slug=29-en-9249&alias=41210-csp29-8-e-210&Itemid=270&lang=en
3. Schwartz KL, Kwong JC, Deeks SL, et al. Effectiveness of pertussis vaccination and duration of immunity. CMAJ. 2016; 188(16): E399–E406.
4. Lewnard JA, Grad YH. Vaccine waning and mumps re-emergence in the United States. Sci Transl Med 2018; 10(433).
5. Hamami D, Cameron R, Pollock KG, Shankland C. Waning Immunity Is Associated with Periodic Large Outbreaks of Mumps: A Mathematical Modeling Study of Scottish Data. Front Physiol. 2017; 8:233.
6. http://polioeradication.org/polio-today/polio-now/this-week/
7. Blumberg LH, Prieto MA, Diaz JV, Blanco MJ, Valle B, Pla C, Durrheim DN. The preventable tragedy of diphtheria in the 21st century. Int J Infect Dis. 2018; 71:122-123.

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• VPD epidemiology
• Immunization coverage and determinants
• Surveillance of re-emergence of VPD
• Vaccines development and vaccination strategies
• VPD re-emergency costs
• Cross-bordering
• Vaccine hesitancy
• Waning immunity