Journal of Pharmacy And Bioallied Sciences

: 2021  |  Volume : 13  |  Issue : 5  |  Page : 31--35

COVID and animal trials: A systematic review

Muhamood Moothedath1, Muhaseena Muhamood2, Yadnit S Bhosale3, Aseem Bhatia4, Pranav Gupta5, Medapati Rama Haranadha Reddy6, Rahul V C Tiwari7,  
1 Department of Oral and Dental Health, College of Applied Health Sciences in Ar Rass, Qassim University, Buraydah, Saudi Arabia
2 Department of Biomedical Dental Science, College of Dentistry, Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia
3 Department of Prosthodontics and Crown and Bridge, MGM Dental College and Hospital, Navi Mumbai, Maharashtra, India
4 Bachelor of Dental Surgery, Gian Sagar Dental College and Hospital, Baba Farid University of Health Sciences, Faridkot, Punjab, India
5 Ex- Senior Resident, Department of Conservative Dentistry and Endodontics, Himachal Institute of Dental Sciences, Paonta Sahib, Himachal Pradesh, India
6 Department Oral and Maxillofacial Surgery, Panineeya Mahavidyalaya Institute of Dental Sciences and Research Center, Hyderabad, Telangana, India
7 Department of OMFS, Narsinhbhai Patel Dental College and Hospital, Sankalchand Patel University, Visnagar, Gujarat, India

Correspondence Address:
Muhamood Moothedath
Department of Oral and Dental Health, College of Applied Health Sciences in Ar Rass, Qassim University, Buraydah
Saudi Arabia


Extensive work is being done to form targeted drugs against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection; however, it is imperative to have a safe and effective vaccine against the same to win the war against this pandemic. For creating an efficacious vaccine, a proper animal model needs to be selected which can have an acceptable similarity of response as well as effects when administered to humans. For the present research, extensive search was conducted in MEDLINE and bioRxiv and medRxiv servers which were published in the English language from January 1, 2020, to August 20, 2020. Search terms included animal models, SARS-CoV-2, COVID-19, immune response against coronavirus, nonhuman primates, mice, ferrets, and macaques. In our study, creating an adequate immune response mimicking the response as in humans, as the endpoint, was considered as inclusion criterion while assessment of any additional therapies like safety as well as minimal tolerable dose using animal models as well as formation of adequate sample size of these models against COVID-19 was not considered. In our search, 163 articles were shortlisted, of them only 20 articles were finally included in our study which addressed to our inclusion and exclusion criterion. Our research articles focused on nonhuman primates, mice, hamsters, ferrets, cats, and dogs, with the main goal to investigate the role of animal models in the pathogenesis of COVID-19. It was evident in our research that animal models only mimic limited signs and symptoms experienced in COVID infection as compared to infections in humans. However, they are still essential to understand the pathogenesis, transmissibility of viral particles, and vaccine testing.

How to cite this article:
Moothedath M, Muhamood M, Bhosale YS, Bhatia A, Gupta P, Reddy MR, Tiwari RV. COVID and animal trials: A systematic review.J Pharm Bioall Sci 2021;13:31-35

How to cite this URL:
Moothedath M, Muhamood M, Bhosale YS, Bhatia A, Gupta P, Reddy MR, Tiwari RV. COVID and animal trials: A systematic review. J Pharm Bioall Sci [serial online] 2021 [cited 2022 Jul 6 ];13:31-35
Available from:

Full Text


Coronavirus pandemic has affected more than 400 thousand people around the world and has been causing severe respiratory syndromes, which also has been a cause for the mortality of the people affected. This disease has been commonly referred to as coronavirus disease 2019 or COVID-19.[1] Older people above 60–65 years and those having comorbidities are seriously affected and thus end up with multi-organ failure leading to death of the patient.[2] Spike protein binding is the main aspect which hastens the entry of virus particle inside human cells, which is facilitated by binding with angiotensin-converting enzyme-2 (ACE 2) protein on the host cell.[3] This increases the propensity of the infection, with mortality rate up to 5.8% with an average of 3.4% and covering almost 210 countries worldwide.[4],[5] Hence, it is a matter of great concern that progress in the field of drug and vaccine development is increased at a breakneck speed. Pharmaceutical companies are trying to manufacture a potent vaccine by either using a weakened virus/or viral particle, viral RNA, or utilizing the target mechanism of spike protein, which allows entry of virus inside host cells.[6] An effective and prompt immune response against this virus is the endpoint considered in vaccine studies. Hence, to generate a high-level immune response, certain specific antigens are considered as the ideal candidate for vaccine production, but it requires host as well. This is where animal models come into the picture so that testing can be done easily without harming human lives.[7] However, currently, the animal models used for production of vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are still under testing phase for many vaccine candidates, and more so the virus should induce similar pattern of disease and pathogenesis, as in humans, for successful vaccine generation.[8] Therefore, it is important to summarize if any of the animal models which are being currently used are turning out to be effective host reservoir.


Search strategy and selection criteria

A systematic review was hence conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-analysis guidelines[9] where studies which had laid emphasis on the generation of animal models against coronavirus infection were considered as the endpoint [Table 1].{Table 1}

Included studies

Researches where animal models were used for vaccine generation against COVID-19 infection were considered. Articles which were between January 1, 2020, and August 20, 2020 were included in the review.

Excluded studies

During the course of searching articles for our systematic review, the articles where only abstracts were available and the ones which were based on SARS and Middle East respiratory syndrome (MERS) as primary infection were excluded from our search criteria. Articles which were published in languages other than English were also excluded.

Data extraction

Data from articles were extracted individually by two reviewers, which were used to construct the tables.

Quality assessment

Quality of each publication was evaluated by two independent reviewers. This review addressed various domains: vaccine production, quality of immune response, active immunity, dose of administration, and pathogenesis of the disease in animal models.

Assessment of risk of bias and applicability in included studies

Assessment of risk of bias and its inclusion in the studies were comprehended by reviewers independently. SYRCLE's risk of bias tool was used for quality evaluation of animal studies and Nature Publication Quality Improvement Project score sheet was used to assess in vitro studies.[10],[11]


During our search on MEDLINE and various other Internet platforms and servers, we identified 69 studies and 94 preprints, of which 143 articles were excluded as many were not original articles, not related to COVID-19 infection. Only 20 articles were consistent with our inclusion and exclusion criterion. Our research articles focused on nonhuman primates, mice, hamsters, ferrets, cats, and dogs, with the main goal to investigate the role of animal models in pathogenesis of COVID-19 infection, risk of transmission, rate of infectivity, and inoculation with SARS-CoV-2 viral strains with ascending doses and studying the therapeutic effects [Table 2].{Table 2}

Rhesus macaques

In case of rhesus species, they have a similar amount of ACE-2-binding receptor proteins on their cells. Hence, they turn out to be near ideal choice for testing of vaccines.[12] In their case, pulmonary infection is present when inoculated with SARS-CoV-2 virus and can be verified with the help of radiographs. They also have an increased number of viral particles that can be extracted from their nose and throat samples.[13]


Ferret models are similar to human lungs as they are susceptible to coughing and sneezing reflexes, so they can be used to test COVID-19 infection also.[14] They also have high transmissibility rates, as ferrets can spread the virus with the help of direct contact and/or aerosols.[15]


Laboratory mice is always an effective and much more cost-effective and easy to handle animals for vaccine testing. Recently, humanized mice versions which have similar ACE2 numbers have also been created to successfully test SARS-CoV-2 infection.[16]

Syrian hamster

This animal model can also be used for testing as they have similar phenotypic alterations in ACE-2-binding mechanisms as and when compared to human binding sites on the cell membrane, which is an essential requisite for the pathogenesis of COVID infection.


Many animal models have recently been included in various studies which have proved to be hopeful for effective vaccine generation. Moderna, a USA-based company, has already completed its phase I trials successfully which helps in safety as well as toxicity of these vaccine targets in humans.[6] Pfizer is already in phase III trials and according to some, the vaccine generated by them is around 90% effective. Many studies of animal models have been reviewed in connection with SARS and MERS infection, these models usually failed to replicate the conditions which are similar to the human environment for trail and testing of vaccines. In addition, the results of this systematic review are also consistent with the above findings when COVID-19 infection is considered.[17] However, viral titers which were high in number were discovered in the respiratory passage, and many mild symptoms were similar to the symptoms that humans experience. Unfortunately, the common complications like acute respiratory distress syndrome (ARDS) and coagulopathy, which is common in human COVID patients, were not replicated in any of these animal models.[18] Most cases that end up in intensive care units have hypoxemia which is caused due to ARDS and coagulopathy leads to severe thrombo-embolic complications in humans, even in the young age population.[19],[20] The postmortem studies of the individuals who died of these complications revealed extensive hyalinization and inflammatory cell damage leading to destruction of the alveolar air spaces which are essential,[21] further supported by the fact that in these individuals, many micro- and macrothrombi were noted in the lung tissue which compromised their lung perfusion leading to higher mortality.[22] A full-blown COVID infection in humans significantly differs from these animal models, as the severity of respiratory as well as thrombo-embolic manifestations is not simulated to near ideal situations. However, mechanism of respiratory symptoms as well as pathogenesis is not fully clear as many pathways may lead to an increase of tissue factor which will cause endothelial injury and hence thrombotic episodes with complement activation, which further compromises the vascular system, especially in the pulmonary area which further worsens the symptoms by activating the clotting cascade and subsequent formation of thromboemboli. Hence, animal models which can simulate these conditions will help in understanding the pathogenesis better.[23],[24],[25],[26],[27] Rhesus macaques and mice were used to test both the antiviral medications and vaccine candidates where the medication stopped viral replication leading to a recovery in case of pneumonitis.[28] In case of vaccine candidates, there was an increase in titer of anti-COVID antibodies as well as a decrease in the viral load which helped in preventing respiratory infection significantly.[29] This leads to a promising outcome for vaccine efficacy as well as antiviral medication effectiveness against SARS-CoV-2. Unfortunately, even after the epidemics such as SARS and MERS, scientists have not been able to form an effective animal model to create conditions appropriate for the spread of COVID-19 in animals.[30],[31] Primates have similar binding affinity to COVID-19 virus as when related to humans,[32] which differs in stark contrast to other animals such as hamsters and mice, which have low-to-medium affinity. This issue has been seen in many studies where mice does not support increased SARS-CoV-2 replication as compared to a chimera as the former does not have more amount of ACE-2-binding protein receptors on their cells.[33] Recently, complex phenotype of COVID-19 was found with the help of single-cell RNA genomic sequence technology which might help us to decide on the dissimilarities between primate and nonprimate species-specific infections.[34] For proper entry of viral particles inside the host cell, it is imperative to study the variations encountered in the distribution of ACE-2-binding protein and TMPRSS2, as the amount of these receptors as well as their surface configuration varies in different organs as well as between two species also. In the primate lung when compared with human pneumocytes, ACE-2 expression was lower in the animals, especially in type II pneumocytes.[35] During the course of evolution, lot of modifications have happened, which has led to the limitation of this viral infection in only the respiratory system of these animals.[36] This explains that animal models show less of symptoms as compared to humans, which poses a practical challenge in vaccine development for humans in case of COVID-19 infection. Our systematic review did have its share of limitations, as we had included preprints in the studies which were not peer-reviewed as yet. We also did have less number of articles studied, and thus, the scope of this study needs to be widened.


Through this systemic review, we were able to find out that animal models only mimic limited signs and symptoms experienced in COVID infection as compared to infections in humans. However, they are still essential to understand the pathogenesis, transmissibility of viral particles, and vaccine testing. Hence, an animal model should be selected carefully, which can help outlining the vaccine testing strategy effectively.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


1World Health Organization (WHO) (2020a) Coronavirus Disease 2019 (COVID-19) Situation Report. Available from: [Last accessed on 12th November 2020].
2Lai CC, Liu YH, Wang CY, Wang YH, Hsueh SC, Yen MY, et al. Asymptomatic carrier state, acute respiratory disease, and pneumonia due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2): Facts and myths. J Microbiol Immunol Infect 2020;53:404-12.
3Wu JT, Leung K, Bushman M, Kishore N, Niehus R, de Salazar PM, et al. Estimating clinical severity of COVID-19 from the transmission dynamics in Wuhan, China. Nat Med 2020;26:506-10.
4Rosenbaum L. Facing COVID-19 in Italy-Ethics, Logistics and Therapeutics on the epidemic's front line. N Engl J Med 2020;382:1873-5.
5Rajgor DD, Lee MH, Archuleta S, Bagdasarian N, Quek SC. The many estimates of the COVID-19 case fatality rate. Lancet Infect Dis 2020;20:776-7.
6World Health Organization (WHO) (2020b) COVID-19 Situation Report-142. Available from: covid-19-sitrep-142.pdf?sfvrsn=180898cd_6 [Last accessed on 12th November 2020]
7Griffin JF. A strategic approach to vaccine development: Animal models, monitoring vaccine efficacy, formulation and delivery. Adv Drug Del Rev 2002;54;851-61.
8Gralinski LE, Menachery VD. Return of the coronavirus: 2019-nCoV. Viruses 2020;12:135.
9Moher D, Liberati A, Tetzlaff J, Altman DG. Preferred reporting items for systematic reviews and meta-analyses: The PRISMA statement. PLoS Med 2009;6:e1000097.
10Liu Y, Eaton ED, Wills TE, McCann SK, Antonic A, Howells DW. Human ischaemic cascade studies using SH-SY5Y cells: A systematic review and meta-analysis. Transl Stroke Res 2018;9:564-74.
11Hooijmans CR, Rovers MM, de Vries RB, Leenaars M, Ritskes-Hoitinga M, Langendam MW. “SYRCLE's risk of bias tool for animal studies.” BMC Med Res Methodol 2014;14:43.
12Melin AD, Janiak MC, Marrone F, Arora PS, Higham JP. Comparative ACE2 variation and primate COVID-19 risk. Communications Biology. 2020;3:641. [doi: 10.1038/s42003-020-01370-w.]
13Gimbel ME, Minderhoud SCS, Ten Berg JM. A practical guide on how to handle patients with bleeding events while on oral antithrombotic treatment. Neth Heart J. 2018;26:341-51.
14Cameron MJ, Kelvin AA, Leon AJ, Cameron CM, Ran L, Xu L, et al. Lack of innate interferon responses during SARS coronavirus infection in a vaccination and reinfection ferret model. PLoS One 2012;7:e45842.
15Kim YI, Kim SG, Kim SE, Kim EH, Park SJ, Yu, KW, et al. Infection and rapid transmission of SARS-CoV-2 in ferrets. Cell Host Microbe 2020;27:704-9.e2.
16McCray PB Jr., Pewe L, Wohlford-Lenane C, Hickey M, Manzel L, Shi L, et al. Lethal infection of K18-hACE2 mice infected with severe acute respiratory syndrome coronavirus. J Virol 2007;81:813-21.
17Subbarao K, Roberts A. Is there an ideal animal model for SARS? Trends Microbiol 2006;14:299-303.
18Ackermann M, Verleden SE, Kuehnel M, Haverich A, Welte T, Laenger F, et al. Pulmonary vascular endothelialitis, thrombosis, and angiogenesis in COVID-19. N Engl J Med 2020;383:120-8.
19Marini JJ, Gattinoni L. Management of COVID-19 Respiratory Distress. JAMA 2020;323:2329-30.
20Helms J, Tacquard C, Severac F, Leonard-Lorant I, Ohana M, Delabranche X, et al. High risk of thrombosis in patients with severe SARS-CoV-2 infection: A multicenter prospective cohort study. Intensive Care Med 2020;46:1-10.
21Bradley BT, Maioli H, Johnston R, Chaudhry I, Fink SL, Xu H, et al. Articles Histopathology and ultrastructural findings of fatal COVID-19 infections in Washington State : a case series Lancet [Internet], 2020;20:6736. [doi: 10.1016/S0140-6736(20)31305-2.]
22Wichmann D, Sperhake JP, Lütgehetmann M, Steurer S, Edler C, Heinemann A, et al. Autopsy findings and venous thromboembolism in patients with COVID-19: A prospective cohort study. Ann Intern Med 2020;173:268-77.
23Chen G, Wu D, Guo W, Cao Y, Huang D, Wang H, et al. Clinical and immunological features of severe and moderate coronavirus disease 2019. J Clin Invest 2020;130:2620-9.
24Poor HD, Ventetuolo CE, Tolbert T, Chun G, Serrao G, Zeidman A, et al. COVID-19 critical illness pathophysiology driven by diffuse pulmonary thrombi and pulmonary endothelial dysfunction responsive to thrombolysis. medRxiv 2020; 10:e44. [doi: 10.1101/2020.04.17.20057125].
25Mulvey JJ, Magro CM, Ma LX, Nuovo GJ, Baergen RN. Analysis of complement deposition and viral RNA in placentas of COVID-19 patients. Ann Diagn Pathol 2020;46:1-4.
26Gupta N, Zhao YY, Evans CE. The stimulation of thrombosis by hypoxia. Thromb Res 2019;181:77-83.
27Zhang Y, Xiao M, Zhang S, Xia P, Cao W, Jiang W, et al. Coagulopathy and Antiphospholipid Antibodies in Patients with Covid-19. N Engl J Med 2020;382:e38.
28Williamson BN, Feldmann F, Schwarz B, Meade-White K, Porter DP, Schulz J, et al. Clinical benefit of remdesivir in rhesus macaques infected with SARS-CoV-2. bioRxiv [Preprint]. 2020 Apr 22:2020.04.15.043166. doi: 10.1101/2020.04.15.043166. Update in: Nature. 2020 Jun 9;: PMID: 32511319; PMCID: PMC7239049.
29Gao Q, Bao L, Mao H, Wang L, Xu K, Yang M, et al. Development of an inactivated vaccine candidate for SARS-CoV-2. Science 2020;369:77-81.
30Lee N, Hui D, Wu A, Chan P, Cameron P, Joynt GM, et al. A major outbreak of severe acute respiratory syndrome in Hong Kong. N Engl J Med 2003;348:1986-94.
31Zaki AM, van Boheemen S, Bestebroer TM, Osterhaus AD, Fouchier RA. Isolation of a novel coronavirus from a man with pneumonia in Saudi Arabia. N Engl J Med 2012;367:1814-20.
32Damas J, Hughes GM, Keough KC, Painter CA, Persky NS, Corbo M, et al. Broad host range of SARS-CoV-2 predicted by comparative and structural analysis of ACE2 in vertebrates. Proc Natl Acad Sci U S A. 2020 Aug 21:202010146. [doi: 10.1073/pnas.2010146117].
33Bao L, Deng W, Huang B, Gao H, Liu J, Ren L, et al. The pathogenicity of SARS-CoV-2 in hACE2 transgenic mice. Nature 2020;583:830-3.
34Han L, Wei X, Liu C, Volpe G, Wang Z, Pan T, et al. Single-cell atlas of a non-human primate reveals new pathogenic mechanisms of COVID-19. bioRxiv. Pre-print
35Van Doremalen N, Lambe T, Spencer A, Belij-Rammerstorfer S, Purushotham JN, Port JR, et al. ChAdOx1 nCoV-19 vaccination prevents SARS-CoV-2 pneumonia in rhesus macaques. BioRxiv (2020) 586:578–82. [doi: 10.1101/2020.05.13.093195].
36Hagai T, Chen X, Miragaia RJ, Rostom R, Gomes T, Kunowska N, et al. Gene expression variability across cells and species shapes innate immunity. Nature 2018;563:197-202.