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expert reaction to Johnson & Johnson announcing that the single-shot Janssen COVID-19 vaccine candidate met primary endpoints in the interim analysis of its phase 3 ENSEMBLE Trial

Johnson & Johnson have announced topline efficacy and safety data from the Phase III ENSEMBLE clinical trial for their single-shot Janssen COVID-19 vaccine candidate.

This Roundup accompanied an SMC Briefing.


Dr Zania Stamataki, Viral immunologist, University of Birmingham, said:

“These are exciting results and come at a time when there is a desperate need for more vaccines.

“The single shot regimen allows flexibility but it is too early to assess the duration of protection.

“Importantly, the vaccine prevented moderate and severe COVID-19 for multiple variants (57% efficacy for the South African variant compared to 72% protection in the US).

“A valuable addition to our arsenal against COVID-19.”


Dr Sheuli Porkess, Chair of the Policy and Communications Group, Faculty of Pharmaceutical Medicine, said:

“The Faculty of Pharmaceutical Medicine welcomes the latest data on the vaccine developed by Janssen, part of Johnson & Johnson (J&J).

“Whilst progress with vaccination in the UK is accelerating, we have also seen that the virus continues to cause serious illness, hospitalisations and deaths, so evidence from more vaccines is very welcome.

“Whilst the J&J vaccine is not yet approved for use, it will be hopefully be helpful as part of the overall global effort to get as many people vaccinated as fast as possible.

“The J&J vaccine uses viral vector technology with a human adenovirus, which was used in Janssen’s vaccine against Ebola.  With this type of vaccine, the harmless adenovirus transports the genetic code (DNA) for the spike protein into cells which then produce the spike protein, triggering an immune response.

“The data comes from the phase 3 ENSEMBLE trial (a single dose placebo controlled double blind randomized study in 43,793 participants), which was conducted in collaboration with the US government and the US National Institute of Allergy and Infectious Diseases (NIAID).  The studies were conducted in USA, Peru, Mexico, Argentina, Brazil, Colombia and South Africa. 34% of participants were over age 60.

“The vaccine has been developed as a single dose regimen for people aged 18 years and over.

“The vaccine is estimated to remain stable for two years at -20°C (-4°F), at least three months of which can be at temperatures of 2-8°C (36°F–46°F).

“We now have three vaccines approved for use in the UK, the Pfizer/BioNTech vaccine, the Oxford/AZ vaccine, and the Moderna vaccine.  We look forward to seeing the outcome of regulatory review of the J&J vaccine, with many others still in development.

“As with all vaccines that are approved by the MHRA, this vaccine would need to demonstrate rigorous safety and quality standards enabling widespread use.  Effectiveness and safety monitoring would be continued following use of the vaccine in practice.”


Prof Kevin Marsh, Co-lead Covid 19 team at the African Academy of Sciences, and Professor of Tropical Medicine University of Oxford, said:

“The results of the  Johnson & Johnson Single-Shot Janssen COVID-19 Vaccine Candidate announced today are extremely encouraging.

“Particular strengths of the study are its size (over 40,000 people), the spread of participants  over 8 countries and three continents, and a wide range of ages.  It is possible that some people will look at the overall reported efficacy of 66% in preventing moderate to severe COVID-19 and focus on comparisons with potentially higher ‘top line’ efficacy reported for some other vaccines.  This would be  a mistake.  The real headline result is that a single shot vaccine, capable of easy long term storage and administration provided complete protection against hospitalisation and death.  This is important because the immediate requirement of vaccination globally is to limit deaths as quickly as possible.  While potentially important for all regions, these results are especially encouraging  for Africa and LMIC’s globally where the combination of single shot, ease of storage and protection against multiple variants is critical.”


Dr Alexander Edwards, Associate Professor in Biomedical Technology, Reading School of Pharmacy, University of Reading, said:

“Today we hear more great news about new COVID-19 vaccines.  The exciting news regarding the Janssen vaccine is that this entire clinical trial assessed a single dose – rather than two doses used for all previous trials reported.  The type of vaccine is similar to the AstraZeneca/Oxford viral vector, so will require similar manufacturing capacity.

“We need to see more details and eagerly await the detailed trial results.  It’s not possible at this stage to compare the protection provided by different vaccines – each trial has different protocols, and a head-to-head comparison is the only fair way to unpick if one vaccine is better than another.  As we start to build up multiple data sets from many different trials, we can start to understand what types of immune response provide protection – this remains vital to deal rapidly with any further variants.

“There has been great debate about 1 vs 2 doses and timing of doses for the first few vaccines to be rolled out.  Hopefully, whilst this is a different product, this trial starts to provide evidence that single dose vaccination can be protective.  However, because this is a different vaccine product, which may be more effective in single dose than other products, we certainly can’t conclude that a second dose isn’t needed for other vaccines – people must still make every effort to complete a full course of two doses for those vaccines.  The benefits of single dose become clearer as larger scale vaccination takes place, for example when we are at a stage where we can vaccinate whole populations rather than the current focus on protecting the most vulnerable groups and age ranges, so this product could become very useful.”


Dr Michael Head, Senior Research Fellow in Global Health, University of Southampton, said:

“Hot on the heels of the Novavax findings we have further news of an effective COVID-19 vaccine.  The overall observed effectiveness was 66% protection against moderate COVID-19 disease and 85% protection against severe disease.  There are again slight differences in the effectiveness against moderate disease between USA (72%) and South Africa (57%).

“We do need to vaccinate the world, and there’s about 8 billion people out there.  So the chance to have multiple vaccines available is excellent, and a single-dose product of course has advantages in terms of cost and logistics for a large-scale roll-out.  It can also be quickly manufactured at large scale.”


Dr Simon Clarke, Associate Professor in Cellular Microbiology at the University of Reading, said:

“The news of successful clinical trials for the Johnson & Johnson Covid-19 vaccine means a welcome addition to the repertoire.  Like all the other vaccines currently available, it generates an immune response against the virus spike protein.  A cold-causing virus is used to deliver the gene for the spike to our cells so that they make the protein in the absence of any coronavirus.  It is also stable at refrigerator temperature, making it easier to administer in GP practices that don’t have substantial cold chain facilities.  It should also be portable enough to take into care homes and other places that might be hard to reach.

“The trial data revealed some interesting findings.  Efficacy was high in the United States, but was lower in South Africa, decreasing by about a fifth.  Biochemical predictions and limited laboratory studies have suggested that South Africa’s dominant variant may be less susceptible to the actions of the current crop of vaccines.  These data provide further evidence that in humans, the South African variant of the coronavirus may have developed partial resistance to vaccination.”


Prof Sheila Bird, Formerly Programme Leader, MRC Biostatistics Unit, University of Cambridge, said:

“Huge congratulations to Kate Bingham and her UK committee of experts who made the critical sub-selection of 7 from over 200 vaccine-contenders; and their magnificent seven include the top five to date.  KB and her committee have restored experts’ good name!”



All our previous output on this subject can be seen at this weblink:



Declared Interests

Prof Kevin Marsh: “None.”

Dr Alexander Edwards: “No conflicts. (I did some research in the past on subunit vaccines for MERS, but with no commercial connection.)”

Dr Alexander Edwards: “No conflicts. (I did some research in the past on subunit vaccines for MERS, but with no commercial connection.)”

Dr Simon Clarke: “No conflicts of interest.”

None others received.

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