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It’s interesting to note that vaccinating in the face of an ongoing outbreak doesn’t have a terribly long history, even for a disease like measles, where we’ve had a highly effective vaccine for decades. It’s worth reviewing in the light of the rollout of COVID vaccine 1/
As recently as 2005, vaccination in response to measles outbreaks as contra-indicated by WHO 2/
https://www.who.int/csr/resources/publications/measles/WHO_CDS_CSR_ISR_99_1/en/
https://www.who.int/csr/resources/publications/measles/WHO_CDS_CSR_ISR_99_1/en/
The recommendation against outbreak response vaccination was not because concerns about the vaccine itself, but about logistics and relative benefit compared to traditional clinical case support. The case against outbreak response vaxx rested on 3 issues 3/
1. Many in the population would already be immune (from vaccination or prior infection), so non-selective campaigns (where you don’t first know if the recipient is immune) are redundant and the marginal value of each dose, in terms of direct protection, is low. 4/
2. The measles vaccine is cold-chain limited. It doesn’t need ultra-cold like the COVID vaccines, but even 2-8C is hard to maintain in the low-resource settings where most measles outbreaks occur. So to achieve high/equitable coverage to stop outbreaks requires a big lift 5/
3. In an outbreak, where kids are getting sick and dying, any activity that draws resources away from clinical care has to demonstrate that it does more benefit than harm 6/
But those arguments, and the cost-benefit assessment, were predicated on outdated thinking and predictions of models of the speed of measles outbreak spread from the pre-vaccine era. 7/
That changed thanks to the efforts of many, and particularly Epicentre and Medicines Sans Frontieres, who argued for change based on their contemporary experience. 8/
A review of literature in 2006 found that:
1. Contemporary measles outbreaks may last many months, allowing sufficient time for response
2. Outbreak response vaccination resulted in lower spread and morbidity, especially if started quickly 9/
1. Contemporary measles outbreaks may last many months, allowing sufficient time for response
2. Outbreak response vaccination resulted in lower spread and morbidity, especially if started quickly 9/
Critically, they further found that vaccination response must be planned around the local needs of the community experiencing the outbreak. One size did not fit all 10/
This effort led to a change in 2006 to recommend vaccination as a frontline response to measles outbreaks, especially in under-resourced areas with high mortality rates. This change only occurred because of the efforts and documented experience of the humanitarian community 11/
See Section 1 F here: https://apps.who.int/iris/bitstream/handle/10665/70047/WHO_IVB_09.03_eng.pdf;jsessionid=FFEB4D299F2053C7325A7754148200FD?sequence=1 12/
Even with a well-established, gold-standard vaccine, like measles, the challenges of cold-chain and distribution prevented it’s use in outbreak response until 2006. The challenges that lie ahead for the COVID vaccines should not be taken lightly 13/
Even as vaccine is rolled out, careful thought must be given to resource allocation (case management shouldnt suffer), community mobilization to increase uptake, prevention activities to maximize the potential vaccine benefit, and yes, WHERE and TO WHOM to prioritize delivery 14/
In the cases of measles, age-targeting has been a perennial question — disease is more severe in the young so the question has hinged on what age should be the upper limit of campaigns. Older kids are more likely to already have been infected, and thus immune 15/
So campaigns conventionally targeted only kids under 59 months. A review of CFR by Wolfson ( https://academic.oup.com/ije/article/38/1/192/696766) and several later expert panel reviews showed that CFR drops by ~1/2 after age 5y … so targeting the young addresses CFR and those most likely susceptible BUT 16/
There are always kids >5y that are still susceptible and a 2010 outbreak in Malawi caught the community off guard with many cases between 5-20y. Years of control prevented outbreaks and let many unvaccinated indivs grow older protected by herd immunity https://pubmed.ncbi.nlm.nih.gov/23343504/ 17/
The Malawi experience reopened the “who to vaccinate?” in outbreaks question. Rapid assessment of early outbreak data in DRC in 2011 helped support the decision for mixed age targeting; only vaccinating up to 10y in areas with few older cases 18/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3679826/
Targeted response in an outbreak has always been fraught with both politics, diplomacy, and scientific uncertainty. The longer you wait for consensus, the less potential to impact the outbreak you will have https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2605500/ 19/
“Science" alone cannot solve the vaccine allocation question. Vaccine allocation is a constrained optimization problem — political will, logistics, access, community support all define the constraints. To reduce the problem to a few numbers, absent that context, is absurd 20/
(Note: “science” in quotes above because Science is fundamentally political and good Science will always acknowledges this. To abstract science away from the constraints of the real world is the mark of an armchair “expert”)
The humanitarian community has wealth of experience delivering vaccine in complex crises. We, in the US, must take stock of the social, cultural, structural challenges facing this vaccination effort and look to the learned experience of others to avoid known pitfalls n/
P.S. The above is framed in terms of measles, but this dance between epidemiology, logistics, and politics in vaccine-base outbreak response can be told in terms of
Meningitis: https://www.who.int/csr/resources/publications/meningitis/PICO1_report_1may14.pdf
Influenza: https://science.sciencemag.org/content/325/5948/1705.abstract
Meningitis: https://www.who.int/csr/resources/publications/meningitis/PICO1_report_1may14.pdf
Influenza: https://science.sciencemag.org/content/325/5948/1705.abstract
