COVID-19 is a respiratory illness caused by SARS-CoV-2, a virus that was first reported in Wuhan, China, in 2019 [1]. This disease was declared a pandemic by the World Health Organization (WHO) in 2020 because of the large number of cases reported globally [2,3]. As of July 9, 2023, there were more than 767 million confirmed cases and more than 6.9 million deaths reported globally, with the majority of cases coming from Europe, the United States, and the Western Pacific. However, Africa has reported only 1% of cases and 3% of deaths globally, although this may be due to concerns about inadequate and unreliable testing facilities. According to the WHO COVID-19 dashboard, as of July 5, 2023, there were 43,078 confirmed COVID-19 cases and 846 deaths in Tanzania [4-6].

SARS-CoV-2 is a virus that belongs to the beta-genera of coronaviruses, which include other human coronaviruses, such as SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV) [2]. A phylogenetic analysis of several SARS-CoV-2 isolates revealed that they are genetically closely related to coronaviruses that have been isolated from bat populations, indicating that SARS-CoV-2 is a zoonotic virus that has made its way into the human population. However, as of 2020, zoonotic linkages have not been established [7]. Coronaviruses are a large family of viruses that cause a range of illnesses, ranging from mild to severe, including the common cold and more serious diseases, such as SARS-CoV, MERS-CoV, and SARS-CoV-2, which have had alarming impacts on humans [8-10].

The SARS-CoV-2 virus has evolved and changed due to genetic selection caused by mutations and recombination [11]. A high rate of mutation in SARS-CoV-2 is associated with the rapid emergence of new viral variants. For example, the alpha variant first appeared in Great Britain in November 2020, followed by the delta variant, which dominated the summer of 2021, and at the end of 2021, the omicron variant emerged and dominated the world [12].

The recommended preventive measures for SARS-CoV-2 are threefold. First, infection control should be practiced in areas where community transmission is widespread. Second, personal preventive measures are recommended to prevent community transmission. Third, serial viral testing is recommended in long-term care facilities to identify cases, isolate positive cases, quarantine contacts, and thus prevent outbreaks. Overall, adherence to these measures can reduce the risk of SARS-CoV-2 transmission [13-17].

Vaccines have been crucial tools in the prevention of viral infections for a long time. The development of vaccines to prevent SARS-CoV-2 infection is seen as a highly promising strategy for mitigating the COVID-19 pandemic. By the end of 2020, multiple vaccines had become available for use, and over 40 candidate vaccines were being tested in human trials, with more than 150 in preclinical trials [18]. Several platforms have been used to develop COVID-19 vaccines through traditional methods, such as inactivated or live attenuated viruses, as well as modern platforms, such as recombinant proteins and vectors [19].

According to the US Food and Drug Administration (FDA) and the WHO, to be licensed and approved for use, a COVID-19 vaccine must meet a minimum efficacy criterion of at least 50%, with a lower bound of the 95% CI at 30% [20,21]. To determine efficacy, phase 3 trials are being conducted with a follow-up period of 6 months, and a minimum of 30,000 participants are needed. Once phase III trials demonstrate safety and efficacy according to the minimum efficacy criteria, the FDA makes decisions on vaccine licensure. Regulatory bodies in Canada and European countries also take similar approaches to licensing their vaccines [20]. However, whether Africa can meet these licensing requirements remains unknown. Vaccine manufacturing requires sophisticated technological resources. Although the production of an African-made COVID-19 vaccine is encouraged to address the pandemic effectively, many countries’ vaccine manufacturing capabilities need to be improved with government funding [22-24], which is meagerly the case among most African governments. The storage and handling requirements of vaccines pose operational challenges, particularly in resource-limited settings, such as Tanzania. For example, the Pfizer vaccine requires ultracold storage in specialized freezers. Additionally, the WHO recommends discarding open vials 6 hours after opening or at the end of the immunization session, whichever comes first. The need for vials used to hold vaccines may also pose supply chain issues in Africa. This highlights the need for more African-made vaccines that can consider storage and handling challenges, in addition to other economic, logistical, and sociocultural issues [25]. Owing to limited vaccine supplies, recipient groups in the beginning were prioritized based on the risks of acquiring infection, severe morbidity and mortality, negative societal impact, and transmission to others. The WHO has proposed a framework that takes into account global equity concerns, including the assurance of vaccine access to low- and middle-income countries [21].

The development of vaccines within African countries could help increase their availability and accessibility in the region. One of the initiatives in place is the development of the TANCoV-1.3.20 vaccine candidate in Tanzania.

The TANCoV-1.3.20 is a live attenuated vaccine derived from a novel strain of avian coronavirus (ACoV). The virus was isolated in 2020 in Tanzania from chickens identified with ACoV disease, and confirmed by polymerase chain reaction using spike protein–encoding gene (S1) primers, which revealed a band of 213 base pairs. Preliminary results have shown that the strain TANCoV-1.3.20 cross-reacted with and was neutralized by antibodies from individuals who had recovered from SARS-CoV-2 infection. Results from the virus neutralization test revealed that the geometric mean titer (GMT) of neutralizing antibodies detected in individuals recovered from SARS-CoV-2 infection was log₂ 6.5.

It has been shown that protective immunity provoked by ACoV is associated with the major structural protein, spike (S) glycoprotein, which induces neutralizing antibodies [26]. Neutralizing antibodies against the S-protein have been targeted for the development of protective vaccines and therapies against SARS-CoV-2 infection worldwide.

It has been proposed that the ACoV vaccine may be used against SARS-CoV-1 [27]. Moreover, ACoV does not cause disease in humans [28].

The TANCoV 1.3.20 vaccine is thermostable, can be stored at ambient temperatures, and can be administered via the intranasal route while maintaining safety and stability. Owing to its route of administration, there is no need to use needles or syringes, thereby avoiding needle-stick injuries and disposal challenges. It is in liquid form with a light green color. The dose of the vaccine per nasal drop (25 µL) has a titer of 10⁶ embryo infective dose (EID₅₀) mL^–1.

On the basis of preclinical results from animal models of inbred mice, rabbits, and pigs, the TANCoV-1.3.20 vaccine is tolerable, safe, and immunogenic.

This is a phase 1/2a double-blinded, randomized controlled phase trial that aims to assess the safety, tolerability, and immunogenicity of the TANCoV-1.3.20 SARS-CoV-2 vaccine candidate among healthy participants in the Dar es Salaam and Mbeya regions of Tanzania. In Dar es Salaam, participants are recruited from the general population and communities such as the police and prison forces, while in Mbeya, participants are recruited from the general population.

For the social component, a convergent mixed methods study using separate and parallel administrations of semistructured in-depth interviews and interviewer-administered questionnaires is embedded in the trial. The design enables the generation of an in-depth understanding of aspects of the trial that promote participants’ acceptance of trial participation. The theoretical framework of acceptability (TFA) will be used to guide the assessment of acceptability. The TFA consists of 7 component constructs, namely, affective attitude, burden, ethicality, intervention coherence, opportunity costs, perceived effectiveness, and self-efficacy [29].

A list of all enrolled participants per site, including their demographics and scheduled visits, will be developed to aid in purposive sampling and the scheduling of appointments for informed consent and data collection during follow-up visits.

The sample size for this noninferiority clinical trial was calculated to compare the proportion of seroconversion on day 28 between participants receiving the investigational vaccine TANCoV-1.3.20 and those receiving the standard Sinopharm COVID-19 vaccine. On the basis of prior studies and seroconversion data from the Tanzanian setting, we assumed an 88% seroconversion rate for the control group (Sinopharm) and expected a 90% seroconversion rate in the experimental group. A noninferiority margin of 20 percentage points was set, meaning that TANCoV-1.3.20 would be considered noninferior if its seroconversion rate was not more than 20% lower than that of Sinopharm. Using a 1-sided significance level (α) of .05, 80% power (1−β), and a 1:1 allocation ratio (experimental: control), the required total sample size was estimated at 50 participants per group. The study includes 3 study groups, with 25 participants per arm, resulting in a total planned sample size of 150 participants. This sample size provides sufficient power to establish noninferiority if the lower bound of the CI for the difference in seroconversion remains above the preset margin. The calculation assumes binomial proportions and follows standard methods for noninferiority designs in parallel trials [30].

Table 1 below outlines the allocation of participants across the 3 study groups, comparing intranasal TANCoV and intramuscular Sinopharm vaccines. Each group consisted of 2 arms with a 3:1 randomization to favor the experimental TANCoV vaccine, totaling 150 participants.

With any addition of study participants, an equal number of participants will be randomly included in each of the 3 arms. Participant replacement will be considered in the following circumstances to allow primary analysis to continue as planned: (1) early study termination, (2) loss to follow-up during study screening and the enrollment period, and (3) the loss of samples (blood, peripheral blood mononuclear cells [PBMCs], serum, and nasal swabs) or temperature during transportation from the study site to the central laboratory, which renders them unavailable for analysis. In the course of enrollment and vaccination, sample quality necessitated the increase of sample size to 169; the additional samples were randomly included in each group.

Eligible participants will be randomized to the intervention arm or control arm via permuted block randomization with a block size of 6 stratified by site. This method ensures a balanced allocation of participants among the groups. Participants fulfilling the eligibility criteria will be randomized sequentially, and each participant will have a unique randomization code. A randomization schedule will be created by an independent statistician via permuted-block randomization of variable size.

Before enrollment, the study screening electronic case report form must be completed. When a participant is confirmed to be eligible and has consented to be enrolled, their details will be entered on the next available line of the enrollment register to ascertain the trial number assigned to that participant, which will be used on all trial documents. This number is unique and will not be used for any other participant.

Blinding will be performed for the investigators and participants. Participants receiving the IP through nasal drops will also be provided with a normal saline injection, which is intended to prevent unblinding. Those who receive the Sinopharm vaccine through intramuscular injection will receive normal saline nasal drops (placebo nasal drops), which are also intended to prevent unblinding. Unblinding will be discouraged during vaccination; however, if a trial clinician considers it necessary for a participant’s allocated vaccination to be unblinded, this should first be discussed with the principal investigators and other key investigators. If unblinding is deemed appropriate, the reason for doing so should be recorded. In the event that adverse vaccine reactions are considered possibly related to the study vaccine, the study vaccine will be discontinued for the affected participant.

The clinical sites will be located at Mwananyamala Regional Referral Hospital in Dar es Salaam for the National Institute of Medical Research (NIMR) Muhimbili and the NIMR-Mbeya Medical Research Center in Mbeya, Tanzania.

For the Dar es Salaam site, all safety laboratory tests will be performed at the Muhimbili National Hospital Central Pathology Laboratory, and PBMC processing will be conducted at the National Public Health Laboratory. For the Mbeya site, laboratory tests will be carried out at the NIMR-Mbeya Medical Research Center safety laboratory. All samples for immunogenicity analysis will be analyzed at the NIMR-Mbeya Medical Research Center Immunology Laboratory.

Inclusion criteria are (1) healthy individuals aged 18 to 45 years at screening and who are willing to provide written informed consent, (2) individuals whose BMI falls between 18.0 and 34.9 kg/m², (3) willingness to undergo COVID-19 testing and negative antigen and antibody tests, (4) satisfactory completion of an assessment of understanding before enrollment, (5) resident in Dar es Salaam or Mbeya and willing to remain in the same region for the duration of the study, and (6) consistent use of effective contraception for individuals who can become pregnant and should have a negative pregnancy test at enrollment.

Exclusion criteria are (1) active tuberculosis or other systemic infectious processes elicited by a review of systems, physical examination, and laboratory testing; (2) history of immunodeficiency or chronic illness requiring continuous or frequent medical intervention; (3) HIV, hepatitis B, and/or hepatitis C infection; (4) received blood or blood products or immunoglobulin in the past 3 months; (5) hives or recurrent hives and severe eczema; (6) history of psychiatric, medical, and/or substance abuse problems during the past 6 months; (7) history of grand mal epilepsy or currently taking antiepileptic medications; (8) receiving immunosuppressive therapy; (9) have received experimental therapeutic agents, currently or within the last few months; (10) previously received COVID-19 candidate vaccines such as Janssen, Sputnik, SINOVAC, Sinopharm, Pfizer, and Moderna, or received any live attenuated vaccine within 90 days before enrollment; (11) history of severe local or general reactions to vaccination; (12) lactating mothers; and (13) individuals deemed unlikely to comply with protocol procedures as judged by the investigators.

There will be internal and external monitoring activities as determined by the trial management group. Monitoring activities will include a review of the study progress, AEs, reactogenicity, protocol deviations, laboratory data, and other data available in the database. In addition, visits will include reviewing essential study documents such as participant binders, source documents, regulatory files, case report forms, and study clinics and pharmacies.

All protocol deviations and violations encountered during the study will be documented and reported to the sponsor, the ethics review committee, and regulatory authorities.

At the end of the study, a summary of the study results will be sent to the institutional review board or institutional ethics committee, along with all the required reports, as appropriate, and all the reports will be sent to the regulatory authorities, as applicable. After closing or completing the study, all documents, intervention allowances, and decoding of information, summaries, and reports for the institutional review board or institutional ethics committee and regulatory authorities will be retained in the investigator site file.

The SPIRIT (Standard Protocol Items: Recommendations for Interventional Trials) reporting guidelines were used in preparing this study (Checklist 1) [31].

All participant information will be handled confidentially, and no information that identifies the participant will be revealed to the sponsor or unauthorized personnel. Individual participants will not be identified in the resulting publications and presentations from the trial. The trial will comply with the principles of the Data Protection Act of the country.

This protocol has received ethical approval from the National Health Research Ethics Committee at NIMR (NIMR/HQ/R.8a/Vol. IX/381 and NIMR/HQ.8b/Vol. I/1084), the Mbeya Medical Research and Ethics Committee (SZEC-2439/R.C/V.1/136 and SZEC-2439/R.C/V.1/66), and the Tanzania Medicines and Medical Devices Authority (TMDA-WEB0021/CTR/0012/03 and BC.69/96/21/01). Informed consent will be obtained from the participants as per the protocol.

Regular compensation will be provided to participants to cover their travel, inconveniences, and lunch expenses. For scheduled and unscheduled visits, this amounts to 30,000 Tanzanian shillings (TShs; US $1=2421 TShs) for Dar es Salaam participants and 25,000 TShs for Mbeya participants. If any medication is required as a result of the study, it will also be provided free of charge. In case of hospitalization or if further care is needed, these patients will be covered under the National Insurance Corporation of Tanzania Limited and will be confined to the period of the study.

This study describes the protocol for a TANCoV-1 phase 1/2a double-blinded, randomized controlled trial conducted in the Dar es Salaam and Mbeya regions of Tanzania. The trial is designed to enroll 150 healthy participants aged 18 to 45 years and randomize them in a 1:1 ratio into 3 groups to receive TANCoV-1.3.20 at a dose of 100 µL with a booster, 100 µL without a booster, or 200 µL without a booster. Follow-up is planned for 6 months postvaccination, and analyses will be conducted in Stata in accordance with CONSORT reporting standards.

As of February 2024, recruitment has been completed (N=169). Laboratory testing is ongoing, and data cleaning and statistical analyses are underway. Safety and immunogenicity outcomes will be analyzed after all follow-up visits and laboratory assays have been completed.

Final analyses are expected to be completed by December 2026, and the primary results are expected to be submitted for publication in 2025. Study findings will be reported following CONSORT guidelines, including results for the primary end points (incidence of AEs and immunogenicity outcomes reflecting local, humoral, and cellular immune responses).