The UK now has access to six different Covid-19 vaccine candidates in development, across four different types, representing some 340 million doses.

Priority groups such as frontline health workers, those with serious diseases, the elderly and ethnic minorities are first in line to receive a jab, should a vaccine be approved.

– What types of vaccine have been invested in?

The deals cover four different classes: adenoviral vaccines, mRNA vaccines, inactivated whole virus vaccines and protein adjuvant vaccines.

– But what is the difference?

– Adenoviral vaccines: These are based on weakened versions of adenoviruses, which are a group of viruses that typically infect membranes of the eyes, respiratory tract, urinary tract, intestines and nervous system, and include the common cold.

– mRNA vaccines: Traditional vaccines are made up of small or inactivated doses of the whole disease-causing organism, or the proteins that it produces, which are introduced into the body to provoke the immune system into mounting a response. But mRNA vaccines trick the body into producing some of the viral proteins itself.

– Inactivated whole virus vaccines: Inactivated vaccines contain whole bacteria or viruses which have been killed, or small parts of bacteria or viruses, such as proteins or sugars, which cannot cause disease.

– Protein adjuvant vaccines: An adjuvant is added to some vaccines to enhance the immune response, and has been shown to create a stronger and longer lasting immunity against infections than the vaccine alone.

The use of an adjuvant may reduce the amount of vaccine protein required per dose, which allows more vaccine doses to be produced.

– Which vaccines has the UK secured?

– Novavax vaccine (NVX‑CoV2373)

Type: Protein adjuvant. The US biotech’s vaccine comprises a recombinant nanoparticle technology containing an engineered Covid-19 spike protein and the saponin-based adjuvant Matrix-M designed to enhance the immune response and stimulate high levels of neutralising antibodies.

Doses: Under the in-principle agreement, the UK has secured 60 million doses of the Novavax vaccine.

Progress: The UK is to support and provide infrastructure to Novavax in running a phase 3 clinical trial in the UK, and plans to manufacture its vaccine in the UK with Fujifilm Diosynth Biotechnologies.

Recent clinical data shows the vaccine triggers an immune response greater than that in patients who have recovered from the disease.

– Janssen vaccine (Ad26.COV2.S)

Type: Adenovirus

Doses: Some 30 million doses have been secured from Janssen, which is owned by Johnson and Johnson, and ministers have agreed in principle to co-fund a global clinical study of its vaccine.

Progress: The next phase of clinical trials is expected to begin later this year to look at whether providing two doses of the vaccine candidate to participants provides long-term protection against coronavirus.

– BioNtech and Pfizer vaccine (BNT162b1)

Type: mRNA

Doses: 30 million

Progress: Early phases of clinical trials suggest the vaccine induces a robust immune response in healthy adults. The phase 2/3 study will enrol up to 30,000 participants aged between 18 and 85.

– Valneva (VLA2001)

Type: Inactivated whole virus

Doses: There is an in-principle agreement for 60 million doses. If the vaccine is proven to be safe, effective and suitable, the UK has secured an option to acquire a further 40 million doses.

Progress: Valneva’s site in Livingston, West Lothian, will manufacture the vaccine. Clinical trials are expected to start before the end of the year.

– GlaxoSmithKline (GSK) and Sanofi Pasteur

Type: Protein adjuvant

Doses: 60 million

Progress: Human clinical studies of the vaccine will begin in September followed by a phase 3 study in December.

– Oxford and AstraZeneca (ChAdOx1 nCoV-19/AZD1222)

Type: Adenovirus

Doses: Up to 100 million

Progress: Preliminary results of phase 1/2 clinical trials suggest the vaccine is safe and induces an immune reaction.

Phase 2, in the UK only, and phase 3 trials to confirm whether it effectively protects against the virus are taking place in the UK, Brazil and South Africa.