The database search yielded a total of 4681 citations after duplicates were removed. The titles and abstracts of these articles were screened and 4588 were deemed irrelevant for our review and therefore excluded. The remaining 93 papers were selected for further assessment by full text screening. The PRISMA diagram can be found in Fig. 1, including reasons for exclusion within the full text screening stage. Fourteen out of 20 papers referred to corruption in low- and middle-income countries and 4 out of 20 discussed corruption issues in high-income countries. The remainder of articles did not highlight country-specific examples of corruption and instead included mentions of more general global corruption issues or mechanisms of combatting corruption globally. In addition, 17 pieces of grey literature were identified. Of the instances of corruption revealed in the grey literature, 4 cases occurred in low-income countries, 7 in middle-income countries, and 7 in high-income countries. Most cases of corruption identified were incidents of substandard and/or falsified products (n = 25). The main products that were implicated were hydroxychloroquine/chloroquine (n = 8), PPE (n = 10), COVID-19 vaccines (n = 7), and diagnostic tests (n = 2). The remaining types of corruption identified were collusion (n = 4), embezzlement (n = 2), fraud (n = 4), and concealment (n = 1).

Within the grey literature, the WHO published multiple medical product alerts over the course of the COVID-19 pandemic warning of falsified medical products globally. The WHO published a medical product alert in April 2020 after receiving 14 reports of confirmed falsified chloroquine products in Burkina Faso, Cameroon, Democratic Republic of Congo, France, and Niger [19]. Subsequent medical product alerts were published in August 2021 and May 2022 alerting the public of cases of confirmed falsified remdesivir in Mexico, Guatemala, and India [20, 21]. In addition, in March 2021, the WHO published an alert regarding confirmed falsified COVID-19 vaccines in Mexico that were being administered to patients outside of authorized vaccination programs [22]. Subsequent product alerts were published by WHO regarding confirmed falsified COVISHIELD and Pfizer-BioNTech COVID-19 vaccines in March, August, and November 2021 in Uganda, Myanmar, India, and Iran [22,23,24].

Factors increasing opportunities for corruption

Of the 20 peer-reviewed articles analyzed in this review, all highlighted factors that facilitated corruption. An overview can be seen in Fig. 2. Though there was significant overlap across identified factors, of Vian’s seven factors that increase opportunities for corruption, those most identified in the literature were (1) health care system and structure, (2) discretion, and (3) transparency and accountability. One additional factor was added to Vian’s (2008) framework, demand, since this factor was identified repeatedly in documents as fostering the production and distribution of substandard and falsified medical products [15].

Fig. 2

Factors facilitating corruption during the COVID-19 pandemic

Health care system and structure

The most prominent factor identified as facilitating opportunities for corruption during the COVID-19 pandemic was a country’s health care system and structure. For example, Gnegal (2020) and Tesfaye (2021) indicated that the emergence of falsified medicines was especially prominent in low- and middle-income countries because of limited access to medicines, limited technical capacity and financial resources for quality assurance, and weak pharmaceutical governance [25, 26]. Further, Kohler and Wright (2020) and Moeshoeshoe (2022) noted that falsified vaccines may have been able to surface due to lack of anti-counterfeiting strategies and weak governance [27, 28].

Echoing the academic literature, online publications by the UNODC, the OECD, World Justice Project, and Transparency International highlighted several factors that led to increased corruption risks during the COVID-19 pandemic including relaxed procurement procedures and a lack of oversight of these processes. A UNODC policy brief noted that the increased emergence of falsified and substandard goods is parallel to relaxed procurement procedures in response to increased demand for products such as PPEs and COVID-19 vaccines [29]. In addition, a 2020 OECD brief highlighted that emergency procurement processes elevate corruption risks due to incomplete documentation, making it difficult for bodies to conduct audits. The brief also highlighted that risks are heightened in developing countries where market gaps and inconsistencies in public procurement were already prevalent prior to the pandemic [30]. Lastly, a brief published by U4/Transparency International in April 2021 highlighted several risk factors for corruption during the COVID-19 pandemic including a lack of clear legal framework needed to counter corruption such as effective conflict of interest laws, free access to public information laws, and whistleblower protection [31].

Discretion

Discretion, which Vian (2008/2020) employs to describe the decision-making power of a government official or other person in a position of power, was identified as well as a factor increasing opportunities for corruption during the COVID-19 pandemic [14, 15]. Abbasi (2020) attributed the procurement of substandard tests partly to the presence of a financial conflict of interest between government officials, who had sole decision-making authority, and diagnostic test manufacturers [32]. Mottay (2020) and Jarrett (2020) similarly identified emergence of substandard face masks [33, 34]. Both identified that substandard PPE products may surface due to government officials deciding to engage with private donors and purchase products from unofficial retailers [33, 34].

Transparency and accountability

Within the field of anti-corruption, transparency and accountability are closely related because transparency relates to the active disclosure of decision-making information so that officials can be held to account by the public they serve. The lack of both transparency and accountability were identified in the literature as increasing opportunities for corruption in health systems during COVID-19. Srivastava (2021) attributed the emergence of falsified vaccines to vaccine inequity and lack of transparency [35]. Additionally, policy briefs published by the World Justice Project and UNDP in September 2020 noted relaxation of procurement oversight and enforcement and a lack of safeguards in transparency and accountability mechanisms led to increased corruption risks in the procurement of COVID-19 supplies [36, 37].

Demand

Several papers identified substandard and falsified chloroquine tablets in African countries including Cameroon, the Democratic Republic of Congo (DRC), Kenya, and Niger [25, 26, 38, 39]. Belayney (2020), Gnegal (2020), Tesfaye (2021), and Waffo Tchounga (2021) attributed the emergence of this falsified chloroquine to the increased demand for these medications due to the off-label use of chloroquine for the treatment of COVID-19 leading to shortages and increased market prices [25, 26, 39, 27, 34]. Jarret (2020) highlighted that the production of these falsified products can be highly profitable due to the high demand for and limited supply of vaccines during the COVID- 19 pandemic [34].

Anti-corruption, transparency, and accountability (ACTA) mechanisms

Of the 20 peer-reviewed studies, 10 discussed potential anti-corruption, transparency, and accountability (ACTA) mechanisms that could be implemented to reduce corruption risks in the procurement and distribution of health products. Of Vian’s typologies for addressing corruption in the health sector (2020), the literature identified anti-corruption approaches, standardized monitoring, transparency interventions, accountability interventions, and systems-level approaches [14]. It is important to note that these typologies are not discreet and there is therefore overlap across categories. The identified mechanisms included the establishment of screening technologies such as Raman spectroscopy or chromatography that can detect substandard medicines (standardized monitoring), transparency in procurement processes (transparency interventions), punitive sanctions for those that sell or distribute falsified products (accountability interventions), and creating legislation and systems in place prior to health emergencies (systems-level approaches).

Anti-corruption approaches

Within the grey literature, 7 documents from international organizations provided guidance on measures to reduce corruption during the COVID-19 pandemic. A guidance note published by the World Bank Group in April 2020 offered possible anti-corruption mechanisms that may be beneficial during the COVID-19 pandemic [39]. This included that legislation and executive orders should be put in place to outline responsibilities for the oversight of the procurement of goods as well as activation of explicit processes for documenting procurement transactions [40]. Similarly, a May 2020 policy brief by OECD highlighted the need to create detailed guidelines on procurement strategies during crises including policies for audit and oversight [30]. The World Justice Project published a policy brief which reinforced the notion that regardless of how expedited procurement processes are, procurement should still be auditable and outline considerations justifying the expedited process [36].

In September 2020, the UNDP published a guidance note on transparency, accountability, and anti-corruption services that can be utilized towards COVID-19 response and recovery [37]. Priorities that were highlighted include strengthening of internal and external oversight and audit capacity within institutions [37]. In addition, this note highlighted the importance of encouraging participation of civil society to enhance procurement oversight [37]. A UNDP policy paper highlighted the need for the creation of a specialized committee with a strong anti-corruption mandate to oversee the prioritization, distribution and monitoring of vaccine programmes and act as a critical oversight body [37].

Standardized monitoring

With respect to implementation of screening technologies, Gnegal and colleagues (2020) suggest utilization of simple and inexpensive screening technologies such as thin layer chromatography or Raman spectroscopy in low-and middle-income countries [25]. For example, the Ecumenical Pharmaceutical Network (EPN) is a non-profit organization that offers quality pharmaceutical services across Africa has monitored medicine quality in countries using thin layer chromatography. Use of this screening technology allowed for identification of falsified chloroquine tables in private and informal markets in Cameroon and the Democratic Republic of Congo [25].

Transparency interventions

Several guidance publications highlighted the benefit that e-procurement platforms could have on reducing corruption risks in procurement processes. To begin, a policy brief published by the OECD in May 2020 suggested leveraging e-procurement platforms to record transactions and create easily accessible tools to allow for public oversight of emergency procedures [30]. On April 7, 2021, a research brief from U4 and Transparency International underscored measures to mitigate corruption risks in the COVID-19 vaccine rollout [37]. This research brief encouraged the use of open contracting and e-procurement for COVID-19 to mitigate corruption risks [37]. Similarly, a UNDP policy paper highlighted the benefit that e-procurement and open contracting can have on reducing corruption risks [37].

Systems-level approaches

Within the grey literature, 7 documents from international organizations provided guidance on measures to reduce corruption during the COVID-19 pandemic. A guidance note published by the World Bank in April 2020 offered possible mechanisms that may be beneficial during the COVID-19 pandemic [40]. This included that legislation and executive orders should be put in place to outline responsibilities for the oversight of the procurement of goods as well as activation of explicit processes for documenting procurement transactions [40]. Similarly, a May 2020 policy brief by OECD highlighted the need to create detailed guidelines on procurement strategies during crises including policies for audit and oversight [30]. The World Justice Project published a brief which reinforced the notion that regardless of how expedited procurement processes are, procurement should still be auditable and outline considerations justifying the expedited process [36].

Barriers and facilitators to the implementation of ACTA mechanisms

Overall, only 5 papers in the academic literature discussed facilitators of and/or barriers to implementation of ACTA mechanisms. In relation to the implementation of standardized monitoring systems, Gnegal (2020) and Moshoeshoe (2022) identified the lack of funding as an important barrier to the implementation of these technologies in low- and middle-income countries [25, 27]. Moeshoeshoe (2022) highlighted the importance of involvement of international stakeholders such as the World Health Organization and UNODC to make implementation possible in resource-limited nations [27]. An additional factor that Moshoeshoe (2022) identified as a barrier to implementing screening technologies is the immature regulatory framework that exists in low and middle-income countries such as those in Sub-Saharan Africa [27].

Several papers identified increased transparency in procurement of health products as a mechanism to reduce corruption within health systems. Within this literature, Abbasi (2020) acknowledged a barrier for implementation of transparency mechanisms is the need to accelerate availability of diagnostics and treatments to support innovation [32]. None of the mentioned articles studied the implementation of proposed ACTA mechanisms and therefore did not discuss barriers to implementation.