Wednesday, September 27, 2023

What Are Viral Vector Vaccines

How Do Viral Vector Vaccines Work

What are viral vector-based vaccines and how do they work?

Scientists began creating viral vectors more than 40 years ago.1 Viral vector vaccines use a modified version of a virus to deliver genetic instructions to the bodys cells. The cells then produce harmless pieces of the virus called antigens which trigger an immune response in the body.

If you are exposed to the real virus later, your immune system will recognise it and know how to fight it. Vaccines which use a viral vector have been approved for the prevention of Ebola and COVID-19 and are in development for the prevention of other diseases, including malaria, influenza and HIV.1,2,3,4

How Easy Are They To Manufacture

A major bottleneck for viral vector vaccine production is scalability. Traditionally, viral vectors are grown in cells that are attached to a substrate, rather than in free-floating cells – but this is difficult to do on a large scale. Suspension cell lines are now being developed, which would enable viral vectors to be grown in large bioreactors. Assembling the vector vaccine is also a complex process, involving multiple steps and components, each of which increases the risk of contamination. Extensive testing is therefore required after every step, increasing costs.

Subunit Recombinant Polysaccharide And Conjugate Vaccines

Subunit, recombinant, polysaccharide, and conjugate vaccines use specific pieces of the germlike its protein, sugar, or capsid .

Because these vaccines use only specific pieces of the germ, they give a very strong immune response thats targeted to key parts of the germ. They can also be used on almost everyone who needs them, including people with weakened immune systems and long-term health problems.

One limitation of these vaccines is that you may need booster shots to get ongoing protection against diseases.

These vaccines are used to protect against:

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Getting The Most From Your Treatment

  • Try to ensure you attend your appointment for your vaccine dose. If you are unable to attend an appointment, cancel your unwanted appointment and book an alternative.
  • You are advised not to drive for the first 15 minutes after your vaccination, in case you begin to feel unwell. Do not drive if you feel dizzy, drowsy or otherwise unwell.
  • It will take at least 14 days after your second dose of AstraZeneca vaccine, or single dose of Janssen vaccine, before you get maximum protection against COVID-19 infection.
  • After you have been vaccinated, continue to follow any local restrictions or guidelines to help prevent the spread of COVID-19 infection.
  • Maintain hygiene measures such as routinely washing or sanitising your hands.
  • If you are having an operation or dental treatment, tell the person carrying out the treatment that you are planning to have, or have had the AstraZeneca or Janssen vaccine.

How Do Such Vaccines Trigger Immunity

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Viruses survive and replicate by invading their hosts cells and hijacking their protein-making machinery, so it reads the virus genetic code and makes new viruses. These virus particles contain antigens, molecules that can trigger an immune response. A similar principle underpins viral vector vaccines – only in this case, the host cells only receive code to make antigens. The viral vector acts as a delivery system, providing a means to invade the cell and insert the code for a different virus antigens . The virus itself is harmless, and by getting the cells only to produce antigens the body can mount an immune response safely, without developing disease.

Various viruses have been developed as vectors, including adenovirus , measles virus and vaccinia virus. These vectors are stripped of any disease-causing genes and sometimes also genes that can enable them to replicate, meaning they are now harmless. The genetic instructions for making the antigen from the target pathogen are stitched into the virus vectors genome.

There are two main types of viral vector-based vaccines. Non-replicating vector vaccines are unable to make new viral particles they only produce the vaccine antigen. Replicating vector vaccines also produce new viral particles in the cells they infect, which then go on to infect new cells that will also make the vaccine antigen. The COVID-19 viral vector vaccines under development use non-replicating viral vectors.

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Who Should Get The Vaccines

The viral vector vaccines are approved for those 18 years of age and older. More information, including how to register for the vaccine, can be found on the BCCDC website:

If you had, or may have had, COVID-19 you should still get the vaccine. This is because you may not be immune to the virus and/or variants of the virus that causes COVID-19 and could get infected and sick again.

Viral Vector Vaccines Have Been Rigorously Studied For Safety

Viral vector COVID-19 vaccines are safe and effective.

Viral vector COVID-19 vaccines have been held to the same rigorous safety and effectiveness standards as all other types of vaccines in the United States. The only COVID-19 vaccines the U.S. Food and Drug Administration will make available for use in the United States are those that meet these standards.

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Are There Additional Considerations To Getting The Vaccine

Speak with your health care provider if you:

  • Were diagnosed with inflammation of the heart by a physician after a previous dose of COVID-19 mRNA vaccine without another cause being identified
  • Had cerebral venous sinus thrombosis with thrombocytopenia or heparin-induced thrombocytopenia
  • Have a history of immune thrombocytopenia
  • Are at increased risk for venous thromboembolism
  • Have a history of multisystem inflammatory syndrome following COVID-19
  • Have symptoms of COVID-19

If you have a new illness preventing you from your regular activities, you should wait until you have recovered. This will help to distinguish side effects of the vaccine from worsening of your illness.

Facts About Viral Vector Covid

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Viral vector COVID-19 vaccines cannot give someone COVID-19 or other illnesses.

  • Viral vector COVID-19 vaccines cannot cause infection with COVID-19 or with the virus used as the vaccine vector.

They do not affect or interact with our DNA.

  • The genetic material delivered by the viral vector does not integrate into a persons DNA.

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How Do Antibodies Protect The Body

Antibodies are a key component of the body’s immune response to a virus. Antibody tests can be used to detect whether the immune system has produced antibodies against a virus after natural infection or vaccination. Everyones immune system is different and responds differently to viruses some people who have been infected by a virus may not have antibodies.5

Heterologous Viral Vectors Vaccines

Heterologous viral vector vaccines consist of a combination of two or more vectors encoding either the same or different antigens that can be administered together or in prime/boost regimens. HVVV immunizations can be advantageous to induce higher magnitude and more durable immune responses compared to homologous vector vaccination. Immunization of rhesus monkeys with a combination of VSV, vaccinia virus , and Ad5- vectors expressing SIVmac239 Gag, in concert with 3M-052 adjuvanted protein resulted in protection from viral challenge in 67% of the vaccinated animals, which was superior to the protection observed in animals vaccinated with adjuvanted protein alone . Interestingly, the study found that HVV vaccination induced potent anti-Gag CD8+T cell responses that reduced the threshold of neutralizing antibodies required to confer durable protection.

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The Different Types Of Covid

This article is part of a series of explainers on vaccine development and distribution. Learn more about vaccines from how they work and how theyre made to ensuring safety and equitable access in WHOs Vaccines Explained series.

As of December 2020, there are over 200 vaccine candidates for COVID-19 being developed. Of these, at least 52 candidate vaccines are in human trials. There are several others currently in phase I/II, which will enter phase III in the coming months.

Who Should Not Get The Vaccine

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You should not get the vaccine if you:

  • Have a serious allergy to polysorbate 80 which is in both of the viral vector vaccines. It is also found in medical preparations and cosmetics
  • Have a history of capillary leak syndrome
  • Experienced thrombosis with thrombocytopenia after a dose of viral vector vaccine

Speak with your health care provider if you had anaphylaxis after a previous dose of a COVID-19 vaccine or if you have had anaphylaxis with an unknown cause.

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Any Vaccine Granted Eua Will Have Undergone Thorough Review

Just as the Pfizer and Moderna vaccines underwent careful review before being granted EUA, so has Johnson & Johnson’s viral vector COVID-19 vaccine.

Not only was this vaccine rigorously tested for safety and effectiveness via clinical trials, the trial data was then scrutinized by several panels of experts. And while it may seem like this vaccine was developed quickly, know that testing and safety were not sacrificed for speed.

“All in all, before being made available to the public, Johnson & Johnson’s viral vector COVID-19 vaccine went through preclinical testing, three phases of clinical trials and external review by two independent panels of experts and two civil service scientific reviews,” explains Dr. Sostman.

How Does The Immune System Respond To Viral Vector Vaccines

The immune response includes the production of specialised cells called B-cells and T-cells. B-cells produce antibodies which either attach to a virus and prevent it from infecting cells or tag a virus for destruction. T-cells recognise and destroy the bodys cells that have been infected by a virus to stop them producing more viruses. Some B-cells and T-cells also work as memory cells which enables the immune system to respond quickly and effectively if the body ever encounters the virus.

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What You Need To Know

  • Viral vector vaccines use a vector virus, which is a harmless, modified version of a virus that does not cause COVID-19.
  • The vector virus delivers important instructions to our cells on how to recognize and fight the virus that causes COVID-19.
  • Researchers have been studying and working with viral vector vaccines for .
  • Like all vaccines, viral vector vaccines benefit people who get vaccinated by giving them protection against diseases like COVID-19 without them having to risk the potentially serious consequences of getting sick.

Johnson & Johnsons Janssen COVID-19 vaccine is a viral vector vaccine. Learn more about Johnson & Johnsons Janssen COVID-19 vaccine, including who can get it, doses, and ingredients.

What Are The Possible Reactions After The Vaccines

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Vaccines are very safe. It is much safer to get the vaccine than to get COVID-19. The vaccines are not live virus vaccines and cannot give you COVID-19. Common reactions to the vaccines may include soreness, redness, swelling and itchiness where the vaccine was given. For some people, these reactions may show up 8 or more days after getting the vaccine. Other reactions may include tiredness, headache, fever, chills, muscle or joint soreness, swollen lymph nodes under the armpit, nausea and vomiting. These reactions are mild and generally last 1 to 2 days. If you have concerns about any symptoms you develop after receiving the vaccine, speak with your health care provider or call 8-1-1 for advice.

The following rare events have been reported after getting the viral vector vaccines:

  • Thrombosis with thrombocytopenia syndrome: serious blood clots have been seen at a rate of about 1 case in 50,000 first doses of AstraZeneca vaccine and 1 in 600,000 second doses. The rate after a dose of Janssen vaccine is about 1 case in 100,000 doses
  • Immune thrombocytopenia: a temporary drop in the blood cells that help prevent bleeding may occur in less than 1 in 10,000 people
  • Guillain Barré Syndrome: a condition that can result in weakness and paralysis of the bodys muscles may occur in 1 in 100,000 people
  • Venous thromboembolism: a blood clot that starts in a vein may occur in about 1 in 10,000 to 1 in 1,000 people after getting the Janssen vaccine

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Why Are There So Many Vaccines In Development

Typically, many vaccine candidates will be evaluated before any are found to be both safe and effective. For example, of all the vaccines that are studied in the lab and laboratory animals, roughly 7 out of every 100 will be considered good enoughto move into clinical trials in humans. Of the vaccines that do make it to clinical trials, just one in five is successful. Having lots of different vaccines in development increases the chances that there will be one or more successful vaccinesthat will be shown to be safe and efficacious for the intended prioritized populations.

What Is A Viral Vector Vaccine

Viral vector vaccines use a modified version of a virus to deliver instructions to our cells to make a protein. In the case of COVID-19 Vaccine Janssen, the viral vector belongs to the adenovirus family . It contains the genetic instructions for our cells to make the spike protein on the surface of SARS-CoV-2 .

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Is One Type Of Vaccine Better

The viral vector-based COVID-19 vaccines developed by AstraZeneca and Johnson & Johnson have been linked to an extremely rare and potentially life-threatening blood-clotting syndrome called vaccine-induced thrombotic thrombocytopenia which is the combination of low platelet counts with blood clots.

The risk for developing this syndrome is estimated to be anywhere from one case in 100,000 doses to one case in 250,000.

In Canada, there have been only seven reported VITT cases in all of the approximately 1.7 million doses of AstraZeneca that have been administered in the country so far.

Due to the extremely low risk of developing VITT after vaccination with a viral vector-based vaccine, however, NACI recently reaffirmed that the mRNA vaccines are preferred over the other ones and that it might be in the best interest of some Canadians who have a low risk of exposure to COVID-19 to wait for an mRNA dose.

Despite this guidance, both Health Canada and NACI have emphasized that the vaccines by AstraZeneca and Johnson & Johnson are safe and effective for the majority of the population and there could be far worse consequences of contracting COVID-19.

Messenger Rna Vaccinesalso Called Mrna Vaccines


Researchers have been studying and working with mRNA vaccines for decades and this technology was used to make some of the COVID-19 vaccines. mRNA vaccines make proteins in order to trigger an immune response. mRNA vaccines have several benefits compared to other types of vaccines, including shorter manufacturing times and, because they do not contain a live virus, no risk of causing disease in the person getting vaccinated.

mRNA vaccines are used to protect against:

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Vaccine Types By Delivery Methods

Currently, all coronavirus vaccines available, regardless of the different types of technology they are based on, are administrated by injection. However, various other types of vaccine delivery methods have been studied for future coronavirus vaccines.


Intranasal vaccines target mucosal immunity in the nasal mucosa which is a portal for viral entrance to the body. These vaccines are designed to stimulate nasal immune factors, such as IgA. In addition to inhibiting the virus, nasal vaccines provide ease of administration because no needles are involved. Nasal vaccines have been approved for influenza, but not for COVID-19.

There are a variety of intranasal COVID-19 vaccines undergoing clinical trials. Examples include a vaccine candidate which uses a modified avian virus as a vector to target SARS-CoV-2 spike proteins and an mRNA vaccine delivered via a nasal nanoparticle spray.


A universal coronavirus vaccine is effective against all coronavirus viruses. The concept was publicly endorsed by NIAID director Anthony Fauci, virologistJeffery K. Taubenberger, and David M. Morens. In March 2022, the White House released the “National COVID-19 Preparedness Plan”, which recommended to accelerate development of such vaccines.

One strategy for developing such vaccines was developed at Walter Reed Army Institute of Research . It uses a spike ferritin-based nanoparticle . This vaccine began a Phase I clinical trial in April 2022.

Some Viral Vector Vaccines Require Only A Single Dose

One of the most exciting things about the viral vector COVID-19 vaccine from Johnson & Johnson is that you only need one dose.

“While both the Pfizer and Moderna mRNA vaccines require two doses separated by several weeks, the Johnson & Johnson viral vector vaccine requires only a single shot,” says Dr. Sostman.

A single dose not only makes things easier on you, but it will likely also help speed up distribution of this vaccine.

“Requiring only a single dose isn’t a general feature of viral vector vaccines, however. This advantage is specific to the Johnson & Johnson COVID-19 vaccine. Other viral vector COVID-19 vaccines, such as the one developed by Oxford-AstraZeneca, still require two doses,” adds Dr. Sostman.

That being said, you may eventually need a booster dose of the J& J vaccine to help prolong protective immunity. Anyone who is 18 years of age or older and received the J& J vaccine at least two months ago is eligible for a second dose of the vaccine.

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What Are Mrna Vaccines

For their COVID-19 vaccines, Pfizer-BioNTech and Moderna use a novel technology that has never been approved for widespread use before the pandemic.

This technology uses messenger ribonucleic acid , which is a molecule that provides cells with genetic instructions for making proteins that are needed for numerous cellular functions in the body, including for energy and immune defence.

In a lab, scientists develop synthetic mRNA that is able to instruct the bodys cells to develop that same distinctive spike protein from the SARS-CoV-2 virus that the viral vector-based vaccines also target.

After the piece of protein is made, the cell breaks down the genetic instructions and gets rid of them. Both Health Canada and the CDC stressed that the mRNA never enters the central part of the cell where a persons DNA material is located, which means the vaccine does not affect or interact with DNA in any way.

Like with the viral vector-based vaccines, the immune system identifies the foreign spike proteins produced by the cells and initiates an immune response by building antibodies against them. If the immune system faces the real SARS-CoV-2 virus, it will be ready to fight it off.

While there are similarities in how both mRNA and viral vector-based vaccines instruct cells to create the SARS-CoV-2 spike protein, mRNA vaccines differ in that they dont contain any live virus.

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