Yellow fever preventive mass vaccination campaign in Jigawa State in Nigeria. August 2023. © WHO (World Health Organization) Nigeria

EYE Strategy August newsletter 

Weekly Epidemiological Record (WER)

Distribution of confirmed yellow fever cases and outbreaks, Africa, 2022. © Pan-American Health Organization (PAHO) – World Health Organization (WHO), 2023. All rights reserved. To view full details of the image, click here to open the document. 

The Weekly Epidemiological Record (WER) serves as an essential instrument for the rapid and accurate dissemination of epidemiological information on cases and outbreaks of diseases under the International Health Regulations (IHR) and on other communicable diseases of public health importance, including emerging or re-emerging infections. 

Each year an issue is produced to provide information on the landscape of yellow fever cases and response for the previous year. This includes immunization activities in the at-risk or affected regions and countries. The 2022 issue is now available. Click here to download. 

Last year, cases of yellow fever were identified in 14 African countries (see map above), and widespread virus circulation with occasional spill-over to humans continued in the Americas (see map below).  

Distribution of confirmed human cases of yellow fever in the Americas, 2017–2022. © Pan-American Health Organization (PAHO) – World Health Organization (WHO), 2023. All rights reserved. To view full details of the image, click here to open the document. 

The number of cases increased from 2021, when 11 countries reported confirmed and probable cases. The resurgence of yellow fever in Africa remains the highest it has been in over 20 years.  

Eight reactive vaccination campaigns were conducted in six African countries, protecting an estimated 5 million people against yellow fever for life.  

In the Americas, yellow fever cases were confirmed in Brazil, Peru and the Plurinational State of Bolivia between July 2022 and June 2023.  

In Africa, one of the four outbreaks in 2022 was reported in a country with a history of yellow fever preventive mass vaccination campaigns (PMVCs).  

Localized immunity gaps in high-risk countries present a continued risk of future outbreaks unless those gaps are closed.  

In 2022, cases and outbreaks continued to affect populations that had not been reached by immunization services, such as those living in areas with compromised security, migrant workers, nomadic populations, and zero-dose children and communities.  

These immunity gaps must be assessed, pockets of unprotected and at-risk population groups identified, and tailored vaccination strategies implemented as part of catch-up strategies. (See ‘EYE Strategy yellow fever immunization gap analysis tool’ below). 

Unbridged immunity gaps jeopardize the elimination of yellow fever epidemics; the overarching goal of the EYE Strategy. 

The year 2022 was also notable for a continued urban threat and therefore, potential international spread that could threaten global health security.  

Despite the challenges, priority countries made good progress in implementing the EYE Strategy in 2022, with >41 million people reached through reactive and preventive yellow fever vaccination campaigns in Africa. 

EYE Strategy yellow fever immunization gap analysis tool 

Yellow fever vaccination campaign, Cameroon, May 2022. Cameroon is one of the countries with a history of vaccination that has experienced a resurgence of yellow fever.

The presence of yellow fever outbreaks in countries with past PMVCs and / or Reactive Vaccination Campaigns (RVCs) calls for immunity gap analysis that investigates populations that are susceptible to the disease.  

Outbreaks may occur because of insufficient yellow fever vaccine uptake and low herd immunity. A coverage of at least 80% is required to confer herd immunity. 

Outbreaks in areas with a history of vaccination can be caused by several factors, such as pockets of unvaccinated people that could account for the outbreaks. These can include high-risk populations such as migrants, internally displaced populations, nomads, refugees, and people living in conflict areas. 

For this reason, an immunity gap analysis tool is being developed to identify priority areas for catch-up vaccination and estimate the size of the immunity gap.  

Immunity gaps can disproportionately affect the poorest and most marginalized communities, including those in areas of conflict with limited or no access to healthcare.  

The overall objective is to provide an estimate of the Yellow Fever vaccination immunity gap for the development of national Yellow Fever catch-up vaccination plan.

The tool is a desk-top tool that can be used by anyone without the need for complex modelling. It will be piloted in several countries before finalization, with an anticipated launch next year.

Is vaccine coverage recovering after the pandemic? 

A YouTube short video by our partner, Gavi, the Vaccine Alliance on the increase of global vaccine coverage in 2022. 

While half of lower income countries are yet to reach pre-pandemic levels of vaccine coverage, in 2022, Gavi-implementing countries reached roughly the same number of children as pre-pandemic, and these children now receive more essential vaccines than ever before.  

The number of zero dose children fell by 17% to roughly 10 million. To watch the short video, click here.

Country updates

The map above shows the implementation of yellow fever vaccination campaigns in Africa in 2022, whether preventive or reactive. A version of this can be found in the WER. Click here to download. 

Reactive Vaccination Campaigns (RVCs)  

Central African Republic (CAR)  

Following a confirmed case of yellow fever in a worker in a forest area, an RVC is planned to target ~233,400 people for protection against yellow fever. The vaccination campaign will target the resident population and seasonal workers conducting forest activities. The campaign will launch once the country’s referendum is over; likely to be the end of September. 

Preventive mass vaccination campaigns (PMVCs)  

Yellow fever preventive mass vaccination campaign in Jigawa State in Nigeria. August 2023. © UNICEF Nigeria

Nigeria     

All states with planned vaccination campaigns for 2022 have now been completed, including Bayelsa; the implementation for which was completed in early 2023, rather than 2022 due to flooding.  

In Borno state, the implementation of yellow fever PMVC is ongoing. The implementation has been staggered due to security concerns. The yellow fever PMVC in the state of Jigawa is now complete. 

The Democratic Republic of the Congo (DRC)      

Yellow fever vaccination campaigns in Lomami, Kasai and Central Kasai will be combined with measles round 1 for improved efficiency and are due to begin in September 2023. 13.6 million people will be targeted for protection against yellow fever in this campaign.    

Further PMVCs in Kongo Central, Kwango, Kwilu, and Mai Ndombe are due to take place in October 2023.  

Uganda     

Uganda’s multi-year yellow fever PMVC began on 9th June. This is the first of three phases. Phase two is tentatively planned for February 2024, with no dates for phase to follow.  

The first phase of the vaccination campaign, covering 51 districts in six regions, (Kabale, Kabarole, Hoima, Lira, Gulu, and Arua) is almost complete. Gaps in vaccination in this phase have been identified and follow-up activities are planned for October 2023.  

The campaign has targeted ~13,397,640 people, which amounts to 93% of the population in five of the 51 districts.   

Phase two will target ~16.4 million people in the following regions: Moroto, Mbarara, Kampala, Masaka and Soroti. Phase three will cover the following regions: Mubende, Jinja and Mbale.  

Persons of ages 9 months to 60 years were included in the campaign, as well as the refugee population. 

Publications

The Lancet, Microbe 

This study has identified what is believed to be the first known transmission of live, attenuated yellow fever vaccine virus through solid organ transplantation to four organ recipients, causing severe neurological disease and two deaths.  

Because the source of infection in the organ donor was a blood product obtained from a recently vaccinated blood donor, the investigation highlights the risk of transmission of live vaccine virus strains through blood transfusions. Read more by clicking here.