COVID-19 vaccines explained: a comparison with veterinary vaccines shows what’s really new and not so new

By Zoltan Penzes
By Zoltan Penzes

Head of Biology R&D, Ceva

Never before in their 225-year history have vaccines been so relevant and important to the health and wellbeing of the global population.

Photo: Benjamin Lehman

The last year has witnessed unparalleled efforts by scientists and clinicians around the world to develop, test and deploy vaccines against Covid-19.

These efforts have led to remarkable achievements: vaccines that have now become household names are being rolled out at huge scale less than a year after the disease was first diagnosed. 

Currently there are over 300 vaccine candidates in development, with about 60 having reached the human clinical phase.

These vaccines span the spectrum of vaccine types, ranging from the conventional, such as live attenuated whole virus and inactivated whole virus, to the more innovative vaccine technologies, such as sub-unit, viral vector and RNA vaccines. 

Although vaccines against human coronaviruses are in their infancy, vaccines against coronavirus infections in poultry, such as infectious bronchitis virus (IBV), have been used for decades.
In fact, 12 billion birds were vaccinated with Ceva’s live attenuated avian coronavirus vaccines range in 2020.

Vaccines against IBV

Below, I will try to explain the basic features and benefits of the different types of vaccine and give some examples of Covid-19 vaccines and other types of human and animal vaccines, including Ceva’s own vaccines that fall into each type.

Animation and illustration by Toby Morris in collaboration with Siouxsie Wiles

Types of Vaccine

An “obvious” way to make a vaccine is to take the disease-carrying virus or bacterium, or one very similar to it, and inactivate or kill it using chemicals, heat or radiation. This approach uses technology that’s been proven to work in people and vaccines can be manufactured on a reasonable scale. 

However, it requires special laboratory facilities to grow the virus or bacterium safely, can have a relatively long production time, and depending on the type of antigen it will likely require one or two doses to be administered.

Covid-19 vaccines

Sinovac’s CoronaVac, Sinopharm, China.

Examples of other human vaccines

Inactivated Salk strain polio vaccine.

Some influenza vaccines.

Veterinary vaccines

Cevac EDS K against egg drop syndrome
Cevac IBD K, against infectious bursal disease, also known as Gumboro disease
Cevac Megamune K, which provides protection against Newcastle disease, different strains of avian coronavirus infectious bronchitis virus, egg drop syndrome and avian pneumovirus infections. 

Key features, benefits and disadvantages

Do not contain any live bacteria or virus, so cannot cause the disease against which they are designed to protect.
Depending on the antigen, may not create such a strong or long-lasting immune response as live attenuated vaccines. Pre-immunization may be needed.

Adjuvant

Yes, adjuvants are typically used.

Number doses needed

Typically require booster doses.

A live-attenuated vaccine uses a living but weakened version of the virus or one that’s very similar. This approach uses technology that’s been proven to work in people and animals and vaccines can be manufactured on a reasonable scale. However, vaccines like this may not be suitable for people with compromised immune systems, and the safety in general have to be carefully assessed.

Covid-19 vaccines

COVI-VAC, Codagenix Inc, USA & Serum Institute, India (not yet licensed).

Examples of other human vaccines

Original Sabin polio vaccine, Measles, mumps and rubella (MMR) vaccine.

Veterinary vaccines

Cevac IBird, Cevac Mass L and Cevac IBron against avian coronavirus infectious bronchitis virus.

Key features, benefits and disadvantages

Provide good broad-spectrum immune responses. 
COVI-VAC is administered intra-nasally.

Adjuvant

No.

Number doses needed

Single, but combination of vaccines is known to increase the broadness of protection (e.g. for avian coronavirus infectious bronchitis virus). Live vaccines can also be used as a “prime”, and then followed by inactivated (killed) vaccines as a “booster”.

A subunit vaccine is one that only uses the very specific parts (the subunits) of a virus or bacterium that the immune system needs to recognize. It doesn’t contain the whole microbe. The subunits are typically peptides or proteins, maybe sugars.

Covid-19 vaccines

Novavax, USA

Examples of other human vaccines

Hepatitis B, whooping cough, tetanus, diphtheria, meningococcal meningitis.

Veterinary vaccines

Ceva’s Leish-Tec vaccine against the parasitic disease leishmaniosis in dogs.

Key features, benefits and disadvantages

Tend not to produce such strong or long-lasting immune responses as live attenuated vaccines.

Adjuvant

Yes, typically needed.

Number doses needed

Depends on the antigen, but repeat doses initially and booster doses may be needed.

This type of vaccine uses a safe virus as a vector to deliver the genetic information for a specific sub-parts – called proteins, or antigens – of the germ of interest so that it can trigger an immune response without causing disease. To do this, the genetic instructions for making particular parts of the pathogen of interest are inserted into a safe viral vector. The safe virus then serves as a platform or vector to deliver this information into the body, where the specific proteins (antigens) are subsequently produced. These proteins then trigger the immune response. This type of vaccine can be developed and updated rapidly, once the vector system based on a safe virus has been already established (this requires extended research).

Covid-19 vaccines

Oxford-AstraZeneca vaccine, UK
Sputnik V, Russia Johnsons & Johnson, USA.

Examples of other human vaccines

Ebola, influenza, hepatitis C, HIV, malaria, tuberculosis, MERS and to deliver various gene therapies. 

Veterinary vaccines

Ceva’s Vectormune range, in use since 1994. In 2020, 7 billion birds were vaccinated against Newcastle disease with Vectormune ND, one of the most widely used poultry vaccine in the world.

Key features, benefits and disadvantages

Long-term immune responses are generally produced. The viral vectors are selected to be safe by nature, and can be further modified e.g. to prevent their replication in the body and increase the immune responses. 

Adjuvant

No.

Number doses needed

One or two doses may be needed, depending on the vector used and the antigen. 

Unlike vaccine approaches that use either a weakened or dead whole microbe or parts of one, a nucleic acid vaccine just uses a section of genetic material that provides the instructions for specific proteins, not the whole microbe. DNA and RNA are the instructions our cells use to make proteins. In our cells, DNA is first turned into messenger RNA, which is then used as the blueprint to make specific proteins. 

A nucleic acid vaccine delivers a specific set of instructions to our cells, either as DNA or mRNA, for them to make the specific protein that we want our immune system to recognize and respond to. 

The nucleic acid approach is a new way of developing vaccines. Before the Covid-19 pandemic, none had yet been through the full approvals process for use in humans, though some DNA vaccines, including for particular cancers, were undergoing human trials. Because of the pandemic, research in this area has progressed very fast and some mRNA vaccines for Covid-19 are getting emergency use authorization, which means they can now be given to people beyond using them only in clinical trials.

Covid-19 vaccines

Pfizer/BioNTech and Moderna, both USA.

Examples of other human vaccines

New technology – no other vaccines currently licensed for use in humans.

Veterinary vaccines

Ceva’s genomic platform holds promise for future development. In some countries RNA vaccines have been already used on a platform basis for veterinary purposes.

Key features, benefits and disadvantages

Genetic vaccines can be updated very rapidly. Needs to be stored at ultra-low temperatures, complicating distribution logistics.

Adjuvant

No, but an RNA delivery technology is typically needed.

Number doses needed

Repeat initial doses needed.

People often ask, what is the best vaccine against Covid-19. The answer is simple – the one that is available to you! All licensed vaccines are safe and have good efficacy, especially against severe illness and death.

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Zoltan Penzes – Head of Biology R&D, Ceva

*Types of vaccines definitions adapted from The World Health Organisation.

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