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Debunked: No, Covid-19 vaccines didn't 'skip' or 'fail' animal trials

All four vaccines approved for use in Ireland have been tested on animals as well as humans.

A NUMBER OF posts circulated on social media recently have claimed Covid-19 vaccines which have been approved for use did not go through animal trials as part of their development process.

The above post has been widely circulated on Facebook by various different pages and individuals, with some shared hundreds of times. 

Commentators in videos on both Facebook and Instagram who acknowledge trials did take place have claimed that vaccines approved across the world “failed” animal trials.

These claims are false.

The European Medicines Agency (EMA), the regulatory body that has approved the four vaccines currently being used in Ireland, requires vaccine developers to provide data from animal trials.


The US Food and Drug Administration (FDA) also requires results from laboratory testing in animals as part of the Emergency Use Authoriazation process for Covid-19 vaccines.

The animal trials are part of the non-clinical phase, before the widely publicised clinical trials on humans. These “in vivo” studies show how the vaccine triggers an immune response and works to prevent infections.

All four vaccines in use in Ireland – Pfizer/BioNTech, Moderna, AstraZeneca and Janssen (Johnson & Johnson) – have conducted and published data on animal trials.


In September 2020, Pfizer announced preliminary pre-clinical data on mouse and non-human primate (monkeys) models.  In a pre-clinical study, testing the vaccine on rheus macaques, it was shown to induce neutralising antibodies.

Another study in mice also found the vaccine generated immune responses.  In the macaque model, an immune profile believed to promote vaccine safety was indicated. 


In June last year pre-clinical data from a study on mice was published in Nature. The study demonstrated that the Moderna vaccine elicited neutralising antibodies in mice. 

Then in July, Moderna published results of an animal study in the New England Journal of Medicine. 

The study showed a two-dose vaccination schedule led to a robust immune response and protection against Sars-CoV-2 infection in the upper and lower airways of non-human primates. 

Overlap: In the case of both the Pfizer and Moderna vaccines, developers were given approval to simultaneously test the vaccines on animals while conducting Phase 1 trials on humans. This overlap made the speed required in the development of Covid-19 vaccines over the last year possible. Both developers had to present the animal trial data before approval. 

Moderna has also conducted some more recent animal trials, testing two new vaccine approaches – a one-dose booster and a separate two-dose regime – against variants of concern on mice. Both approaches yielded positive results, as treated animals showed high levels of antibodies capable of neutralising both the South African and Brazilian variants.


Researchers at Oxford collaborated with scientists at Rocky Mountain Laboratories in Texas, who were the first to test the vaccine on animals – again, rhesus macaques. The animals were given a single dose of the vaccine and then exposed to high levels of the virus.

While other monkeys in the lab became ill, those that had been vaccinated remained healthy.

The study reported good levels of both safety and efficacy when tested on animals. This study took place and the data was reviewed before clinical trials on humans were started. 

Further animal studies also took place in the UK and Australia. 

Johnson & Johnson

In July last year, J&J published a study in Nature that showed its vaccine, when tested on rhesus macaques, elicited a strong immune response and protected against subsequent infection. 

Another trial, which showed that a high dose of the Sars-CoV-2 virus caused pneumonia, weight loss and mortality in hamsters also demonstrated that one dose of the J&J vaccine elicited binding and neutralising antibody responses and protected inoculated hamsters from these serious disease effects. 

The developers launched initial clinical trials on humans based on the strength of the data from the rhesus macaque model. 

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