One-dose Janssen COVID-19 vaccine being approved by the MHRA

One-dose Janssen COVID-19 vaccine being approved by the MHRA

This article was published on
May 28, 2021

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It has been announced that the one-dose Janssen COVID-19 vaccine has today been given regulatory approval by the UK Medicines and Healthcare products Regulatory Agency (MHRA).

It has been announced that the one-dose Janssen COVID-19 vaccine has today been given regulatory approval by the UK Medicines and Healthcare products Regulatory Agency (MHRA).


What our experts say

Context and background


Media briefing

Media Release

Expert Comments: 

Dr Peter English

This is excellent news! It will increase the amount of vaccine available; and the more vaccines that are authorised for use, the less chance there is that a glitch in supply (“biological” products like vaccines can easily be derailed this way) or a new safety concern will have a harmful effect on vaccine uptake. We need to get all UK adults – and indeed, the rest of the world – vaccinated as soon as ever possible.

This vaccine, commonly referred to in Europe as the Janssen vaccine, and in the USA as the Johnson & Johnson vaccine, is very similar to the Oxford AstraZeneca, and the Sputnik V vaccines, being another adenovirus vector vaccine. The New York Times published a good “explainer”.[1] It has been in use in the USA since April,[2] and received European Medicines Agency recommendation in March.[3]

Before a vaccine can be approved for use in the UK, the Medicines and Healthcare Regulatory Authority (MHRA) has to review extensive safety and efficacy data. Like its US counterpart (which published a lot of the details of its assessment[4]), it will have reviewed safety and efficacy data from pre-marketing studies completed by the manufacturers, and effectiveness and safety data from postmarketing data in countries (like the USA) where it has already been in use (eg [7]).

Like the other vector vaccines (and in contrast to some of the mRNA vaccines), the Janssen vaccine does not need “ultra-cold” or freezer storage, so it fits well into the standard UK vaccine cold-storage supply infrastructure.

Like another vector vaccine, there have been concerns that there may be an increase in a rare form of blood clotting events. This delayed the authorisation in the US,[2] and likely also in the UK. Any slight increase in risk of vaccine-associated blood clots has to be kept in proportion, given the much greater risks of clotting events and other complications following Covid-19 disease.

Head-to-head trials of vaccines have not been undertaken, and there is, so far, very little data that allows meaningful comparison of vaccines. Each has been trialled at different times, with different circulating variants; in different places, with different demographics, and using different trial protocols.

The big difference between the Janssen vaccine and other vaccines is that it was authorised for use as a single-dose vaccine. It will be very interesting to see whether it is actually as effective, following a single dose, as other vaccines are after two doses. This will be especially important when considering effectiveness against variants such as the “India” B.1.617.2 variant, against which some other vaccines appear to be considerably less effective until after the second dose.[6] It may be that there is actually little difference between the real-world effectiveness of a single dose of any of the vaccines, and that the difference is that Janssen/Johnson & Johnson were bold enough to expect the vaccine to be efficacious enough after a single dose to base their authorisation applications on such data; I understand that further trials are ongoing to look at other dosing options (more than one dose, and amount of vaccine).

  1. Corum J, Zimmer C. How the Johnson & Johnson Vaccine Works. New York Times 2021; Updated 22 Mar 2021; Accessed: 2021 (23 Apr): (
  2. Tanne JH. Covid-19: US authorises Johnson and Johnson vaccine again, ending pause in rollout. BMJ 2021;373:n1079. ( or
  3. European Medicines Agency. EMA recommends COVID-19 Vaccine Janssen for authorisation in the EU. European Medicines Agency (EMA) News 2021; Updated 11 Mar 2021; Accessed: 2021 (11 Mar): (
  4. Vaccines and Related Biological Products Advisory Committee. FDA Briefing Document. Janssen Ad26.COV2.S Vaccine for the Prevention of COVID-19: Federal Drug Administration, 2021 (26 Feb); 1-62 ( or via
  5. Daugherty SE, Guo Y, Heath K, Dasmariñas MC, Jubilo KG, Samranvedhya J, et al. Risk of clinical sequelae after the acute phase of SARS-CoV-2 infection: retrospective cohort study. BMJ 2021;373:n1098. (
  6. Lopez Bernal J, Andrews N, Gower C, Gallagher E, Simmons R, Thelwall S, et al. Effectiveness of COVID-19 vaccines against the B.1.617.2 variant [public pre-print]: Public Health England, 2021 (22 May);  (
  7. Shay DK, Gee J, Su JR, Myers TR, Marquez P, Liu R, et al. Safety Monitoring of the Janssen (Johnson & Johnson) COVID-19 Vaccine — United States, March–April 2021. Morbidity and Mortality Weekly Report (MMWR) 2021; Updated 07 May 2021; Accessed: 2021 (28 May): (

Prof Arne Akbar

Having a range of vaccines against COVID-19 is important in helping us defeat this pandemic, so news that the Medicines and Healthcare products Regulatory Authority (MHRA) has today approved a fourth COVID-19 vaccine for use in the UK is extremely welcome.

The Janssen vaccine is a viral vector vaccine like the AstraZeneca/Oxford vaccine and works in a similar manner.  The main difference between these two vaccines however is that the Janssen vaccine only needs to be given as a single dose.

The UK has doses of the Janssen vaccine on order for delivery later this year, so while this approval won’t have an immediate impact on the UK’s COVID-19 vaccine rollout, it is reassuring to know that stocks of this vaccine will be delivered in due course.  The Janssen vaccine is part of an ongoing trial looking at the potential need for booster vaccine doses later in the year – the results of this will be important in determining how supplies of this vaccine can be best utilised when they arrive.

Safety in vaccines is always paramount and the MHRA will have carefully scrutinised the evidence on this COVID-19 vaccine to ensure that it is both safe and effective.  Although all COVID-19 vaccines have been developed in a shorter timeframe than normal, all the same rigorous safety standards and checks have still been carried out.  With previous studies showing the Janssen vaccine is 67% effective in stopping infection and 85% effective in preventing severe disease, this vaccine will be an important additional tool in stopping the spread of COVID-19 within our communities.


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