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Coronavirus

Explainer: The difference between COVID-19 mRNA and Adenovirus-vector vaccines

Published: Updated:

When COVID-19 invades our bodies, the virus tries to overcome the immune system. It attacks and multiplies in huge numbers readying itself for the inevitable fightback.

As the pandemic has shown, for many, their immune responses failed to combat coronavirus. The infection killed them.

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Many others fell ill, some seriously, and some slightly, showing few symptoms at all while acting as carriers for the virus’s spread.

It is ultimately the immune system that is the first and last line of defense against infectious disease. It uses a variety of tools to fight off infections, with red blood cells carrying vital oxygen to tissues and organs, and white blood cells acting as the key shield against infecting viruses, bacteria, fungus and other microorganisms.

Helping the body’s immune system, we have multiple medicines at hand.

In the fight against viruses vaccines have benefited Mankind for generations. Polio, Rubella along with many others are blocked by the body’s immune system when boosted by that vaccine.

How do vaccines work?

According to the global vaccine alliance GAVI, all vaccines work by exposing the body to molecules from the target pathogen to trigger an immune response.

When vaccines are introduced into the body, they offer protection by providing our bodies with a supply of memory to help it remember how to fight off the same virus if infected again in the future.

It typically takes two to three weeks after receiving a vaccine for the body to begin to produce its defense mechanism to ensure an effective immune response to defend itself in the event of that future infection.

Director General of the Ghana Health Service Dr. Patrick Kuma-Aboagye receives the coronavirus disease (COVID-19) vaccine during the vaccination campaign at the Ridge Hospital in Accra, Ghana March 2, 2021. (File Photo: Reuters)
Director General of the Ghana Health Service Dr. Patrick Kuma-Aboagye receives the coronavirus disease (COVID-19) vaccine during the vaccination campaign at the Ridge Hospital in Accra, Ghana March 2, 2021. (File Photo: Reuters)

Peoples’ knowledge of vaccines has increased considerably throughout the many months of the pandemic. This is unlikely to change because everyone wants to keep pace with the best ways to protect themselves from COVID-19. New technologies and medicines are likely in the world’s long, continuous fight against COVID-19.

More specifically, different vaccine types will continue to be offered to the public, all of which will defend the body against the virus in different ways.

The best-known vaccines being used fall under two classes: messenger RNA (mRNA), and Adenovirus-vector vaccines. They are the basis for an array of big pharma brand named products.

While these two vaccines have been created from different scientific approaches and designed with unique defense mechanisms against the virus, they have both proven to be quite effective in combatting this pandemic.

mRNA vaccines

A researcher works inside a laboratory of Chulalongkorn University during the development of an mRNA type vaccine candidate for the coronavirus disease (COVID-19) in Bangkok, Thailand, May 25, 2020. (Reuters)
A researcher works inside a laboratory of Chulalongkorn University during the development of an mRNA type vaccine candidate for the coronavirus disease (COVID-19) in Bangkok, Thailand, May 25, 2020. (Reuters)

mRNA vaccines are a new in the disease protection space. Unlike other vaccines that use a weakened or inactivated germ to fight the virus, mRNA vaccines teach a body’s cells how to produce a protein, or just a piece of protein, to trigger an immune response, prompting the production of antibodies which protect us against infection if the real virus were to ever enter our bodies.

The widely accepted – and currently available - types of mRNA vaccines are the jabs manufactured by Pfizer and Moderna. The advantages of both these two-dose vaccines are that they are both highly effective, non-infectious, and have no preservatives in them.

“Messenger RNA is present in our cells naturally and gives instructions for making protein,” Dr. Azeem Abdul Salam Mohamad, Internal Medicine Specialist at Bareen International Hospital in Dubai told Al Arabiya English.

“mRNA in vaccines educates our cells on how to make a piece of spike protein of COVID virus. That way when the actual virus is introduced in the body, the body will already have developed some kind of an immune response,” he added.

RNA based vaccines are quickly designed and manufactured based on genetic sequencing and mRNA fragments don’t cause COVID-19, explained Dr. Mohamad. The fast rate at which these vaccines are produced contributed to their quick approval across the world.

In research conducted by scientists from the Washington University School of Medicine in the United States, it was found that the two mRNA vaccines created a constant immune reaction to the virus in the body protecting itself against COVID-19, online medical news agency Health reported.

The research indicated that booster shots might not be needed to protect against the existing variants unless new strains emerge and are stronger than the two messenger RNA-based vaccines.

“It’s a good sign for how durable our immunity is from this vaccine,” Dr. Ali Ellebedy who is based at the Washington University in St. Louis told the New York Times. “The fact that the reactions continued for almost four months after vaccination - that’s a very, very good sign.”

The results of the study suggested that a vast majority of people who are vaccinated with Pfizer or Moderna would be protected in the long run against existing variants. However, older adults or people with weaker immune systems will need booster shots.

The exact length of the protection provided by mRNA vaccines against the virus has not been determined.

“The disadvantage is that they only allow a fragment of virus to be made, producing poor protective immune response and hence multiple boosters may be needed,” Dr. Mohamad said.

One of the most common misconceptions related to this vaccine type is that it could alter a human’s DNA. This has been debunked by numerous studies on the subject, including GAVI.

Read more: Is it safe to mix-and-match COVID-19 vaccines? Here’s what we know so far

Adenovirus-vector vaccines

Like mRNA, Adenovirus-vector vaccines also use a specific genetic code from the “spike antigen” to protect the body against COVID-19, but it is deployed differently. Instead, the Adenovirus system uses a harmless virus as a vehicle to carry the spike into the body and create an immune response, online news media Mint reported.

A box with Sputnik V (Gam-COVID-Vac) vaccine against the coronavirus disease (COVID-19) is seen at a vaccination centre in Depo food mall in Moscow, Russia June 17, 2021. (Reuters)
A box with Sputnik V (Gam-COVID-Vac) vaccine against the coronavirus disease (COVID-19) is seen at a vaccination centre in Depo food mall in Moscow, Russia June 17, 2021. (Reuters)

Both Oxford’s AstraZeneca and India’s Covishield COVID-19 vaccines use a mild adenovirus which causes common cold in chimpanzees. Russia’s Sputnik V uses human adenoviruses engineered to prevent the replication of a virus. Once these adenoviruses enter the body, human cells begin to produce the antigen to eventually combat the coronavirus.

One of the drawbacks of this vaccine type, from a manufacturer’s perspective, is that it would require live adenovirus to be grown in large quantities in the lab first.

In order to ensure the utmost safety during this process precautions will need to be taken to avoid infecting the people involved in its production.

“One challenge of this approach is that people may previously have been exposed to the virus vector and raise an immune response against it, reducing the effectiveness of the vaccine. Such “anti-vector immunity” also makes delivering a second dose of the vaccine challenging, assuming this is needed, unless this second dose is delivered using a different virus vector,” a report on the GAVI website stated.

Delta variant

The Delta COVID-19 variant, first identified in India, is now the dominant form of the virus in a handful of countries, including the United Kingdom and the United States where it accounts for 10 percent of all diagnosed cases, according to online news media Medical News Today.

Recent data indicates that the available vaccines are highly effective against the Delta strain by preventing a severe reaction and diminishing the need for hospitalization.
Research by Public Health England (PHE) proved this theory, showing that Pfizer-BioNTech’s mRNA vaccine (96 percent) and Oxford-AstraZeneca’s Adenovirus-vector vaccine were highly effective against hospitalization after two doses, accounting for 96 and 92 percent efficacy, respectively.

Further research is needed to determine which is more effective and how well each will protect against future variants.

Read more:

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