I’ve been reading with great interest the most recent issue of Vaccine, which is dedicated to “Building Next-Generation Immunization Supply Chains”.

http://www.sciencedirect.com/science/journal/0264410X/35/17

I particularly enjoyed the following article but was surprised to read that the authors identified a discrepancy between WHO PQS and Gavi Cold Chain Equipment Optimization Platform guidance relating to solar refrigerators and under what conditions (how many hours of mains/generator electricity are available each day on average) they should be considered for vaccine storage.

'When are solar refrigerators less costly than on-grid refrigerators: A simulation modeling study'
http://www.sciencedirect.com/science/article/pii/S0264410X17300555

The article states:

"To effectively maintain an adequate supply of life-saving vaccines in low and middle income countries, where electricity supplies can be capricious [1], the World Health Organization (WHO) currently recommends solar refrigerators for regions with less than four hours of electricity per day, on average, and electric mains-powered ice-lined refrigerators (ILRs) for areas with more reliable electricity [2]. Gavi recommends solar refrigerators for locations with fewer than eight hours of electricity per day or power outages that last more than 48 h [3].
[…]
[2] World Health Organization Department of Immunization, Vaccines and Biologicals Quality, Standards and Safety. PQS devices catalogue: prequalified
equipment for the Expanded Programme on Immunization (EPI); 2016 March 11.
[3] Gavi. Cold chain equipment optimisation platform technology guide; February 2016."

I went back to the PQS Catalogue and the “Selecting a suitable energy source” graphic on page 35 (this also appears in the WHO-UNICEF solar guidance document). My understanding is that the guidance offered here is in fact the same as Gavi's, in other words solar - in addition to other solutions - should be considered at locations with fewer than eight hours of electricity per day (if the answer to the question "On average, how many hours a day is mains/generator electricity available?" is between 0 and 7).

After some thought, I realised that the confusion has probably arisen from the way that solar is presented under the 0-3 box. Under 4-7 it is stated: “Use ice-lined refrigerator* rated 4 hours electricity a day, or consider solar”. However, it seems the “or consider solar” has (understandably) been missed by the authors of the journal article. I don't think this impacts the findings of the article in any way; however, it is worth calling out the discrepancy, as it’s clear that Platform and PQS guidance should be closely aligned if possible (and I think they are).

It may be worthwhile to create a new, clearer version of the PQS graphic. I am in discussion with the PQS team in relation to this and hope to update members in future if a new graphic is developed.

In summary, for a location with 0 to 7 hours of mains/generator electricity available each day, solar, long-term passive, or liquid petroleum gas solutions should all be considered. And for locations with 4 to 7hours of mains/generator electricity, ice-lined refrigerators rated 4 hours electricity a day should also be considered. Refer to the PQS Devices Catalogue for more information.