Covid-19: different types of vaccines and how they work

A range of Covid-19 vaccines are being developed worldwide and the differences between them can be confusing. How do the new mRNA vaccines work? What about vector vaccines? We asked scientists to give us an insight into the different types of Covid-19 vaccines.

Last update : 26 October 2021

Vaccine development is a complex and lengthy process, but it has seen an unprecedented acceleration due to the current pandemic. Massive funding for Covid-19 vaccine research, coupled with worldwide collaboration among scientists and timely assessment of data by authorities, has ushered in a new era for vaccine development.

In the European Union, just one year after the start of the pandemic, four vaccines have been given conditional marketing authorisation. The vaccine developed by BioNTech and Pfizer was authorised on 21 December 2020; the one developed by Moderna on 6 January 2021. The one developed by AstraZeneca on 29 January 2021, and the one developed by Johnson&Johnson/Janssen on 11 March 2021, following positive assessments by the European Medicines Agency (EMA) of their safety, quality and efficacy.

The EMA has also started rolling reviews of a number of other Covid-19 vaccines. These began on 3 February 2021 for Novavax, on 4 March 2021 for Sputnik V, on 4 May 2021 for Vero Cell, and on 20 July 2021 for Vidprevtyn. The rolling reviews will normally continue until enough evidence is available for formal a marketing authorisation application. On 12 February 2021 the EMA also started a rolling review for the vaccine of CureVac AG, but the company itself decided to withdraw from the process in order to focus on a different COVID-19 vaccine development programme.
 

12 Covid-19 vaccines to watch

Company Type Efficacy Doses Storage Status in Europe*

Pfizer / BioNTech 🇩🇪🇺🇸

mRNA

95%

 

💉💉
(💉)

Moderna 🇺🇸
mRNA

💉💉
(💉)

-20°C
AstraZeneca / Oxford 🇸🇪🇬🇧
Adenovirus-vectored technology
💉💉
Fridge
Johnson&Johnson / Janssen 🇧🇪🇺🇸
Adenovirus-vectored technology
💉
Fridge
Novavax 🇸🇪🇺🇸
Protein
💉💉
Fridge
CVnCoV - CureVac AG 🇩🇪
mRNA
💉💉
Fridge
Sputnik V - Gamaleya Research Institute 🇷🇺
Adenovirus-vectored technology
💉💉
-18°C

Rolling review
Emergency use in Hungary, BiH, Serbia, Montenegro

CoronaVac - Sinovac 🇨🇳
Inactivated virus
💉💉
Fridge

Rolling review
Emergency use in Turkey

BBIBP-CorV - Sinopharm 🇨🇳
Inactivated virus
💉💉
Fridge
Emergency use in Hungary, Serbia
VLA2001 - Valneva 🇫🇷
Inactivated virus
Fridge

In development

Sanofi & GSK 🇫🇷 (x2 vaccines)

mRNA & protein

Rolling review of Vidprevtyn
(protein-based vaccine)

Status in Europe: overview of the situation in EU and in the candidates/potential candidates countries.

More information here

Researchers have developed different types of vaccines against SARS-CoV-2, the virus that causes Covid-19. They differ in how the antigen(s) – the active component(s) that trigger a specific immune response against the disease-causing organism – are prepared. Some use the same technologies or platforms as other vaccines that are currently available, while others use approaches that are entirely new, or that were developed recently for the SARS and Ebola vaccines.

The platforms listed below are currently in use in a variety of vaccines:

• Inactivated viral vaccines: produced by culturing the SARS-CoV-2 virus in cell cultures and subsequently destroying its genetic material.
• Live attenuated vaccines: produced by generating a genetically weakened version of the virus that replicates it to a limited extent, enough to induce an immune response but not to cause disease.
• Recombinant protein vaccines: based on the spike protein of the SARS-CoV-2 virus.
Viral vector vaccines: typically based on an existing virus (usually a non-replicating adenovirus) which carries the genetic code that encodes the spike protein.
• DNA vaccines: based on plasmids, modified to carry genes that generally code for the spike protein, which is then produced in the vaccinated individual.
• RNA vaccines: based on messenger RNA (mRNA) which provides genetic information for the spike protein.

Source: nature.com

Ongoing Covid-19 vaccine developments focus on both viral vector and messenger RNA (mRNA) vaccines.

Viral vector vaccines against SARS-CoV-2

A vector can be an adenovirus other than the virus that is being vaccinated against. It has its reproduction gene removed and is used in the vaccine to transport genetic material into specific cells in the body. The gene which causes infection is removed, while a gene with the code of the SARS-CoV-2 spike protein is inserted into the adenovirus. The inserted element is safe for the body but still triggers a specific immune response.

The first and only vector vaccine approved by the EMA is AstraZeneca’s ChadOx-1 Covid-19 vaccine, for which the World Health Organization has also issued an interim recommendation. The first vector vaccine against Covid-19 was the Russian-developed Sputnik V, registered by the Russian health ministry in the summer of 2020. Interim analysis of its phase IIII trial data showed a 91-96 % efficacy rate against Covid-19.

Viral vector vaccines against COVID-19: how they work

What is a viral vector?
Infographic - Viral vector vaccines against COVID-19: how they work
What happens in your body when you get a viral vector vaccine
Infographic - Viral vector vaccines against COVID-19: how they work
An important advantage
Infographic - Viral vector vaccines against COVID-19: how they work

mRNA-based vaccines

With this methodology there is no adenovirus injected into the cells. Instead, a genetic message (mRNA) is injected to stimulate the human cells to produce pieces of spike protein on their surfaces, similar to that present on the surface of the SARS-CoV-2 virus. These trigger an immune response and the body learns to fight off the coronavirus if it enters the body.

Emeritus Earl Brown ESMH scientistProfessor Earl Brown, University of Ottawa: An advantage of mRNA and other expression-vectored vaccines is that production of protein within cells results in the activation of both cellular and antibody dependent immunity, whereas protein-based vaccines generally induce weaker T-cell responses.”Read the full interview

According to Professor Johan Neyts, leader of the RegaVax research group at the KU Leuven, the message sent to the human cells by mRNA and vector vaccines is the same. He says that only the means by which the code is introduced into the cells differs. For example, RegaVax is working on a single-dose Covid-19 vaccine vectored by the original yellow fever vaccine, which not only protects against the foreign pathogen for which the antigen has been inserted, but is also highly efficacious against yellow fever.

Concerns about mRNA vaccines

Some members of the public are concerned that mRNA vaccines could interfere with human DNA, and misinformation about their capacity to transcribe or modify human DNA is circulating online. According to Professor Earn Brown of the University of Ottawa, spike mRNA vaccines will not and cannot change the genetic makeup of human cells because their molecules are not delivered into the nucleus; they become unstable and degrade in a matter of hours.

Professor Earl Brown: The spike mRNA vaccines will not change the genetic makeup of cells because they are not delivered into the nucleus – where DNA resides – but into the cytoplasm.”

How mRNA vaccines protect you against COVID-19

mRNA technology explained in simple terms
How mRNA vaccines protect you against COVID-19 © European Union, 2021
What happens inside your body when you get an mRNA vaccine
How mRNA vaccines protect you against COVID-19 © European Union, 2021
How your body reacts if you are infected with coronavirus, once vaccinated
How mRNA vaccines protect you against COVID-19

Will Covid-19 vaccines protect us against mutations and future coronaviruses?

Professor Brown says that the recent emergence of SARS-CoV-2 variants such as the B.1.1.7 UK variant, which can partially bypass the immunity offered by the first generation of vaccines, has stimulated the development of second-generation vaccines directed specifically against them.

Johan Neyts ESMH scientistProfessor Johan Neyts, KU Leuven: “For the approved vaccines … protection against the UK variants is comparable to protection against the Wuhan strain. Clinical studies with the Novavax and J&J vaccine in regions where the South African strain was circulating demonstrate some reduced efficacy.”Read the full interview

Although the present vaccines will not offer full protection against future novel coronaviruses, Professor Brown says that they may be helpful in regulating the severity of the immune reaction, as seen in different populations. Novel coronaviruses, he added, will require their own dedicated vaccines.

Professor Johan Neyts: In general, vaccines should not be expected to be active against new coronaviruses that may possibly emerge in the future. If new viruses emerge, whether belonging to the coronavirus family or not, new vaccines will need to be developed each time.”

What about efficacy concerns related to vector vaccines?

Taking into consideration the reported 90% efficacy of the Pfizer/BioNTech vaccine, some people worry about the lower percentages for vector vaccines. The AstraZeneca vaccine, for example, was approved with an overall efficacy of 62%.

Professor Neyts underlines that the new data reported by AstraZeneca shows that a longer interval between the first and second doses results in a marked increase in efficacy (up to around 80%). The Sputnik V vector-based vaccine has an efficacy of more than 90%, while the overall efficacy of the Johnson & Johnson vaccine is lower (66%) but it has been observed to offer good protection against severe disease.

“My view on the whole situation is that it is also possible with vector-based vaccines to obtain excellent protection. Fine-tuning of doses and dose schedules may have a further, marked positive impact on efficacy,” he says. “It is also important that the public understand that it is most remarkable that efficacious to very efficacious vaccines have been developed in just one year’s time and that this was not a given”.

“We should also aim to communicate to the public at large that it is logical that not all possibilities for dosing and vaccination schedules could have been explored in a time span of one year (as would have been possible in a normal, longer development process) and thus that one may expect that more optimal dosing and dosing schedules may be suggested based on new studies in the coming months”.

Useful link:
Draft landscape and tracker of COVID-19 candidate vaccines by WHO


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