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Frequently Asked Questions (FAQ) About Adenovirus-Based Vaccines

By Alan Moy, MD

The Institute receives many inquiries about COVID-19 vaccine candidates that are being developed and are either currently being clinically tested or soon to be tested in clinical trials. The most common question that we are asked is which COVID-19 vaccines are derived from aborted fetal cells.  Adenovirus vaccines are the most common vaccines that use aborted fetal cells and are currently receiving the most media attention. Lay people find it challenging to understand how adenovirus vaccines are linked to aborted fetal cells because the science is highly technical and complex. The following are responses to FAQ to adenovirus-based vaccines.

1. What is adenovirus?

Response: Adenovirus is a DNA virus that is a cause of the common cold.  There are several different strains of adenoviruses that are prevalent in humans and animals.

2. How are adenoviruses used as vaccines?

Response: One of more genes of the original adenovirus are artificially deleted so that the virus cannot replicate.  Then a specific COVID-19 gene (usually the gene that encodes for the "spike protein") is inserted into the adenovirus genome. The resulting adenovirus acts as a gene therapy that delivers the spike protein gene into human tissue in which human cells expresses the spike protein, which, in turn, provokes an immune response against COVID-19.

3. How do adenovirus vaccines interface with aborted fetal cells?

Response: Genetically-altered adenoviruses cannot assemble into viral particles unless the protein product of the deleted gene is available. Viruses also cannot replicate without a cell. To resolve the problem, the missing adenovirus gene is placed in HEK293 cells or PER.C6 cells. These human cells synthesize the missing protein necessary to allow the adenovirus to complete its assembly into viral particles. While the final viral particles can infect cells, it cannot replicate because it lacks the missing gene necessary for viral replication. HEK293 is an aborted fetal cell that was produced in the 1970'sThe PER.C6 cell line is an aborted fetal cell line that was produced in the 1980's.

4. Which Current COVID-19 Vaccines Are Using the Adenovirus Method?

Response: AstraZeneca, Johnson and Johnson (Janssen) and CanSinoBio. The federal government invested 456 millions of dollars into Johnson and Johnson’s vaccine and invested over 1 billion dollars into AstraZeneca's vaccine.

5. Has adenovirus-based vaccine achieved prior clinical success?

Response: Adenovirus-based vaccines are largely an unproven vaccine methods. Adenovirus-based vaccines were tested in the past to prevent HIV infections. However, the vaccine failed and actually increased the risk of HIV infections. The clinical trial was stopped for this reason.

6. If a patient has been exposed to the common cold, will an adenovirus vaccine work?

Response: Certain adenovirus strains, such as Ad5, is widely prevalent in many countries because it is a cause of the common cold. Thus, if a vaccine is produced from the Ad5 strain (e.g. CanSinoBio), there is a high probability that the vaccine will not work because an individual will immune reject the vaccine because of previous established immunity.

7. Are there other scientific shortcomings of adenovirus-based vaccines?

Response: One major shortcoming of adenovirus-based vaccines is fact that repeat administration using the same vaccine approach is extremely challenging for the same reason highlighted in item #6. The initial vaccination establishes an immunity that will reject a booster response or will immune reject an adenovirus-based vaccine for a future novel virus.  Thus, an adenovirus vaccine approach may only be used once.

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