WHO’s Interim recommendations for the use of One-dose Janssen Ad26.COV2.S (COVID-19) vaccine

Single dose of the vaccine can increase vaccine coverage rapidly which is an imperative in many countries where level of vaccine uptake is not optimal.  

WHO has updated its interim recommendations1 on the use of the Janssen Ad26.COV2.S (COVID-19).

One-dose schedule of the Janssen vaccine 

Use of either a one- or two-course of the Janssen vaccine can now be considered.  

The one-dose schedule is an EUL (Emergency Use Listing) authorized regimen. 

In some circumstances, using one dose may have advantages.  Many countries face severe vaccine supply constraints, combined with a high disease burden.  A single dose of the vaccine is efficacious and makes it possible to increase vaccine coverage rapidly, which in turn will reduce the burden on health care systems by preventing severe disease outcomes. A single dose may also be a preferred option for vaccinating hard-to-reach populations or populations living in conflict or insecure settings. 

Second dose of the vaccine:  

A second dose may be appropriate as vaccine supplies and/or accessibility increases. Countries should consider offering a second dose, beginning with the highest priority populations (e.g., healthcare workers, older people, people with comorbidities) as indicated in the WHO Prioritization Roadmap.  The administration of the second dose will result in increased protection against symptomatic infection, and against severe disease. 

A heterologous vaccine (e.g., a COVID-19 vaccine from another vaccine platform that has received EUL) can also be considered for the second dose. 

Interval between doses:  

Countries can also consider a longer interval between doses. A second dose 2 months after the initial dose substantially increases efficacy, especially against symptomatic infections, including when caused by SARS-CoV-2 variants of concern.  An even longer interval between the two doses with Ad26.COV2.S (6 months rather than 2 months) has been shown to result in a larger increase in immune responses in adults.  Countries could therefore consider an interval of up to 6 months based on their epidemiological situation, and needs of sub-populations. 


Like Oxford/AstraZeneca’s ChAdOx1, Janssen Ad26.COV2.S (COVID-19) vaccine also uses adenoviruses as vectors. There are evidences to link them to rare side effects of blood clot as they bind to platelet factor 4 (PF4), a protein implicated in the pathogenesis of clotting disorders2



  1. WHO 2021. Interim recommendations for the use of the Janssen Ad26.COV2.S (COVID-19) vaccine. Interim guidance Updated 9 December 2021. Available online at  
  1. Soni R., 2021.Future of Adenovirus based COVID-19 Vaccines (such as Oxford AstraZeneca) in light of recent finding about Cause of rare side effects of Blood clot. Scientific European. Posted 03 December 2021. Available online here  


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