Is there a short cut to prove a vaccine is successful?

Everyone wants a vaccine to be available now.  The UK government announced last week a ‘world first’ in setting up a specialised centre in London to test possible new vaccines by exposing volunteers to the virus rather than waiting for the slower clinical trial.  How likely is it such an initiative would shorten the time to showing a vaccine is successful?  What are the practical and ethical issues involved?  


September 30 09:53 EST
  • There are several clinical trials around the globe currently comparing the rate of infection contracted naturally between a group of volunteers given a new Covid-19 vaccine and a group given a ‘dummy’ vaccine
  • Definitive results of the success of these trials may be available before the end of the year, but that depends on how many people in the studies become infected naturally 
  • In my post of 13 August*, I referred to a letter from 15 Nobel laureates suggesting that waiting for these clinical trials to prove the benefits of any new vaccine would take too long.
  • The letter argued for a speedier process, and 30,000 volunteers had signed up, willing to be deliberately exposed to the virus. This is known as a challenge study.  


  •  The UK government have now committed to establishing a Unit to do just that. 

How will such a challenge study be undertaken?

  • Companies developing vaccines would come to the facility with their product and a study planned to test it.  
  • For each study, the volunteers would be vaccinated and then exposed to the virus.  They would be closely followed up over I guess 2 weeks to determine if they develop of Covid-19
  • According to the press release any affected volunteers would be treated with remdesivir: a drug shown to have a modest effect on reducing the severity of infection in patients admitted to hospital 
  • The version of the virus to which they are exposed has been developed by hVivo, a company experienced in producing strains of viruses for vaccine challenge studies in influenza
  • The strain they developed should be sufficiently similar to the current natural strains, but would produce a milder infection
  • The ‘dose’ of the virus the volunteers are exposed to would need to be determined.  This might involve a few studies, gradually increasing the dose 

Are there ethical issues?

  • Of course, and any company wishing to test their vaccine would need to obtain specific ethical approval
  • The regulators who grant ethical approval will want to review the background information from each vaccine manufacturer very carefully to ensure as far as possible that the risk to any volunteer would be minimal
  • It is obvious that Covid-19 is not flu and young healthy people have (albeit rarely) become seriously ill from Covid-19, which is not easily treatable   
  • There is also awareness that one volunteer who developed severe complication or died from the virus would be a PR disaster, which would affect both the challenge initiative as well as further development of the vaccine
  • There are likely to be very large payments to volunteers.  Volunteers to hVivo’s influenza trials are paid nearly £4000 (in part because they need to be compensated for their time).  We don’t know what the Covid-19 volunteers will be paid , but the recompense might not surprisingly be a consideration in the minds of those who volunteer.
  • It is not an epidemiological question but let me ask you the readers of this blog, what would be an appropriate payment? 

How will the results accelerate vaccine development?

  • This is the area on which I have the greater number of questions!
  • The challenge studies could be done on new vaccines which have yet to be tested in humans or on those vaccines that are already in large scale clinical trials.
  • If the former was the case then the testing could allow a more rapid progression of new vaccines into larger trials than say the 6 months that is the case for current vaccines.  
  • If the latter was the case then I am not sure what the challenge studies would add.
  • As far as side effects are concerned: the clinical trials already underway are studying very large numbers of volunteers, of all ages, and thus hopefully could be big enough to assess the risk of short and long term side effects – which the smaller sized challenge studies cannot do
  • As far as any vaccine being protective is concerned: many vaccine experts are anticipating that a ‘good result’ from a vaccine would be a protection of 60-80%.  Even if a challenge study shows a vaccine stops the occurrence of infection in 100% of the small number of  volunteers; we would still need to await the results of the larger trials
  • There is also the question whether the engineered virus used in the challenge studies is sufficiently similar to the natural virus currently infecting people to be a useful comparison  


Given the stage we are at now with the vaccines under development, I am not sure what advantage this initiative will bring.

If you would like to receive email notifications of new posts on this blog just click this link and enter your email at the bottom of the home page:

One reply on “Is there a short cut to prove a vaccine is successful?”

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s