Human challenge studies in the study of infectious diseases
What can deliberately infecting healthy people tell us about infectious diseases? How is this useful for developing treatments, and how do we manage the risks?

The effect of consumers stockpiling certain goods and the slow reaction of retailers to ration them exposed the limitations of cost-efficient and streamlined supply chains to be agile and adapt to unforeseen shocks. This suggests that changes may be needed to make the supply chain more resilient. Specific problems arose from the closure of parts of the catering sector and the lack of agility in redistributing supplies from this sector to retail outlets or the food donation/charity sector. This was due to challenges in packaging availability, logistics and labelling requirements; leading to an increase in food loss. Agricultural food producers and the wider supply chain may have incurred significant losses from the impacts of COVID-19. Food processing facilities have been responsible for a number of localised COVID-19 outbreaks. This may be influenced by a range of factors, including the proximity of workers for prolonged periods, the need to speak loudly to communicate over the noise of the machines or the shared welfare spaces external to the factory setting. The immediate effects of COVID-19 on the food supply system are the current policy concern, but the longer-term food system issues highlighted as a result of the pandemic will have to be addressed by considering how to build resilience to possible future shocks.
DOI: https://doi.org/10.58248/RR36
Commentators have suggested the COVID-19 pandemic has exposed several vulnerabilities in the UK food system, such as insufficient capacity in domestic food production and labour challenges. The UN Food and Agriculture Organization’s Outlook 2020 has highlighted that food markets will face many more months of uncertainty related to the COVID-19 pandemic. Food prices are expected to remain low, but this will not prevent local, national and international disruptions in food supply chains from impacts on key factors such as transport. When lockdown began on March 23 2020, shoppers found empty supermarket shelves; panic buying compounded the impact of households transferring their food purchases from food services (restaurants and take-aways) – that had closed – to retail stores. The food supply chain responded, with farmers finding new supply opportunities, factories switching capacity to key products, and supermarkets rationing items and increasing home deliveries, especially to those shielding.
Food system shocks illuminate how many parts of government have a role in food policy. Interventions to mitigate disruptions have included:
Several existing and new public-private bodies have supported Defra liaison with the food industry and the creation of a cross-government Food and Essential Supplies to the Vulnerable Task Force. However, the requirement for policy coordination exposes ‘governance gaps’ where food policy responsibilities need clarification, and raises the prospect of needing new governance structures for food policy. For example, policy responses have been largely reactive. These have been in response to private and civil society sectors raising questions about timeliness and preparedness, particularly around emergency food aid, and about the Government’s messaging in relation to panic buying. Evidence submitted by the STFC Food Network+ to the Commons EFRA Committee inquiry on COVID-19 and Food Supply highlighted that policies and guidance were produced reactively as problems emerged rather than being part of a proactive approach. The ripple effects of the coronavirus have exposed other weaknesses and inequalities in the way food is produced and distributed. Evidence submitted by the University of Hertfordshire discussed the exacerbation of a pre-existing critical food system failure that there are high levels of food insecurity caused by poverty, managed through a precarious reliance on charitable provision, such as food banks, with support from the private sector. Stockpiling in the early phase of the pandemic undermined the purchasing ability of food banks and the level of food surplus in food retail businesses that would, in normal circumstances, be redistributed to food banks. This highlighted the vulnerabilities in food redistribution relying on supermarket supplies.
The Centre for Food Policy describes the food system as “the interconnected system of everything and everybody that influences, and is influenced by, the activities involved in bringing food from farm to fork and beyond”. It comprises a range of activities above and beyond producing, processing, packaging, retailing, storing and consuming food. The complexity and connectedness of the food system means that it is vulnerable to a range of shocks and stresses; an action in one part of the system has consequences for other parts. Public health shocks can disrupt the food system by affecting supply through restrictions brought in to tackle the disease, shortages of workers due to the disease or by affecting demand through changes in consumer behaviour. The shock from the current pandemic has increased calls for recognition of the value of a regular supply of high-quality and affordable food. In POST’s survey of over 1,100 experts about concerns relating to the COVID-19 outbreak, over 50 concerns were raised about food supply chain issues, including:
Commentators suggest that COVID-19 has exposed how our current food system has little capacity to fend off disruption, difficulty in stretching to accommodate change, and little redundancy or overlapping systems that provide fail-safe mechanisms. For instance, for some commodities there are two entirely separate supply chains, one supporting supermarkets and the other supporting food service. When demand in the food service supply chain collapsed as a result of pandemic-related shutdowns, prices in the retail supply chain were surging on higher demand, but it proved challenging to move food easily from one chain to another. One reason for this was specific supply chain pinch points, such as unavailability of retail packaging at egg packing stations for the wholesale or food service market. Other issues included the lack of agile capacity to process milk destined for the food service market into retail orientated processing facilities. This has also had an effect on producers that specialised in supplying high-end restaurants with premium goods and led to food waste.
Food system resilience is usually described as the system’s ability to absorb change, adapt or transform, and then return to a steady state after disruption (which may differ from its original state). The UK cross-government Global Food Security research programme has defined a resilient food system as robust (shielded from disruptions) and that can recover quickly after disruption and reorient to accept alternative outcomes (such as accepting seasonal availability of fruit and vegetables). Resilience determines the system’s capacity to maintain a desired state of food security when exposed to stresses and shocks, where stresses are the pressures or tensions gradually exerted on the system, such as climate change, and shocks are more sudden or immediate events, such as the COVID-19 pandemic. While the COVID-19 shock was initially the result of transmission of a virus from animals to humans, the effects of shock were compounded by additional interacting factors, including the stress of increasing food insecurity. The fragility of the food system to a shock depends on exposure and vulnerability, which in turn are determined by a range of social and economic factors. The risk of shocks occurring is also increasing, with rapid changes in global geopolitics and trade, and parallel concern for future climatic events
The 2018 Cabinet Office Resilience Sector Plans include the food supply as one of the 13 Critical National Infrastructure sectors. These are defined as “those critical elements of Infrastructure (facilities, systems, sites, property, information, people, networks and processes), the loss or compromise of which would result in major detrimental impact on the availability, delivery or integrity of essential services, leading to severe economic or social consequences or to loss of life”. Defra holds responsibility for food supply and has worked closely with other agencies and departments to mitigate risks and disruptions, such as with the FSA to consider the risk of COVID-19 associated with food. There is a range of relevant food system responsibilities held by different government departments, such as responsibilities for diet and nutrition and labelling held by the Department for Health and Social Care (DHSC).
Defra’s responsibilities include working with the food industry to plan for and respond to disruptions to food and drink supply chains through the annual Sector Security and Resilience Plans. The food sector resilience plan is a classified document that sets out how the Government and the sector will work together to ensure the resilience of food supply. This plan uses research into building resilience of food supply chains shocks. Such shocks have occurred on a regular basis in the past few decades, including the extreme flooding events during the winter of late 2015 and early 2016. The planning was developed in conjunction with the Food Chain Emergency Liaison Group, a well-established mechanism for Defra and Devolved Administration officials to exchange information regarding threats to the supply chain, and their management, with all the major food industry representatives and retailers. This relies on information being provided by industry on a voluntary basis during the disruption, but the Coronavirus Act 2020 includes a power to act if a member(s) of the food industry refuses to comply with voluntary requests for information.
In evidence submitted to the EFRA inquiry, the NFU highlighted that there is a risk that lasting structural damage will be caused in some agricultural sectors with “a long tail of impacts”. For example, the UK fresh produce sector (fruit, vegetables and salads) faced severe impacts from COVID-19 with the loss of access to seasonal migrant workers due to restrictions on international travel. The Office for National Statistics (ONS) estimates that the UK agricultural sector employs 64,000 seasonal migrant workers; the majority of abattoir workers are from overseas and most abattoir vets are from the EU (75% and 90%, respectively); and an additional 121,000 EU27 citizens are employed in food manufacturing. It is open to question whether the failure rate of farm businesses will remain low, as the rapid closure of the UK catering sector left many of the UK’s 10,000 dairy farms operating at a significant loss. There is also a risk to the global supply continuity of animal feed, supplements and veterinary products, with disruption caused by both export bans to protect supply and drops in demand related to the impacts on meat and dairy production of global restrictions on the catering sector. This economic squeeze impacts on supply chain resilience and the ability to invest in buffer capacity and adaptive capacity.
The agri-food sector contributed £121.0 billion or 9.4% to national Gross Value Added in 2018, but UK food producers in 2017, on average, only made a 1% return on capital employed, compared with 11% for processors, 12% for manufacturers, 8% for wholesalers and 6% for retailers. The Government has put in place a suite of measures for businesses to mitigate economic hardship, but these schemes are not necessarily well-suited to agricultural production as farms cannot be furloughed when animals and crops need to be managed. The Government supported a one-off loss insurance scheme for dairy farmers in England and Wales to access up to £10,000 each to cover up to 70% of their lost income. Up to this year, UK farmers received about £3bn in annual EU subsidies and the free movement of people has provided migrant seasonal labour for harvesting fruit and vegetables to British farmers. The Pick for Britain website was developed collaboratively to support the agricultural sector in avoiding labour shortages, along with other measures such as permitting charter flights from Eastern Europe to bring migrant workers into the UK. Profits in the horticultural sector are comparatively low, with an average farm income of £52,100; land prices in UK remain high and increases in labour costs and loss of productivity from inexperienced labour may reduce profitability further. A report jointly funded by the NFU, British Apples and Pears, British Summer Fruits and the British Growers Association has stated that COVID-19 has resulted in labour costs increasing by up to 15%, which is in addition to a 34% rise in labour costs over the past 5 years.
A systematic review by the London School of Hygiene and Tropical Medicine showed that food processing facilities, operating throughout lockdown periods, had been responsible for a relatively high number of localised outbreaks. The review suggested that the cold atmosphere in this setting has facilitated the spread of the virus. The facilities are kept at about 5°C, a temperature that may keep the virus alive for longer outside the body, with constant air circulation. Other possible explanations included the close proximity of workers for prolonged periods, shared welfare spaces, as well as the need to speak loudly to communicate over the noise of the machines, which could lead to an increased projection of viral particles. Four meat-processing factories in the UK have been at the centre of outbreaks in Wales, Leicester and Cleckheaton in West Yorkshire, a development also seen in other countries such as the US, France, Spain and Germany. Guidance from the US Centers for Disease Control and Prevention has also suggested that the confined working conditions and long periods spent by workers in close proximity – often 10 to 12 hours a shift – mean meat factories are at substantially heightened risk of spreading SARS-CoV-2. In the US, as many as 25,000 meat and poultry workers are reported to have contracted COVID-19, with at least 93 deaths.
Public Health England (PHE), Defra and the FSA jointly advised on social distancing of 2 m between individuals for businesses to minimise the spread, irrespective of the type of operations (now changed to 1 m plus mitigations). Where personal protective equipment (PPE) and social distancing may not be feasible, the FSA suggested the optional use of protective screens and slowing down the speed of the kill line. Evidence submitted to the Commons EFRA Committee inquiry by the STFC Food Network+ recommended that standardised publication of UK Government guidance was needed on PPE, bespoke social distancing applicable in meat processing plants across the UK to overcome discrepancies and inconsistencies and the roll out of routine COVID-19 testing for all staff at abattoirs, not just those showing symptoms.
Evidence to the Commons EFRA Committee from the British Retail Consortium stated that the main difficulty in meeting the rapid increase in retail demand was the logistics of moving food through the supply chain quickly enough, with deliveries to stores increasing by 30%. The food sector operates ‘just-in-time’ supply chains that are linked to demand models. If those demand models suddenly change, as they did during the pandemic, the system can be brittle if contingency plans cannot be enacted rapidly. There may only be a buffer of a few days’ or weeks’ worth of supply within the chain but increasing this would require changing supply chain practices and increasing food storage and processing infrastructure. Without wider improvements to infrastructure to improve basic support for logistics (especially locally and regionally), there is a vulnerability that cannot be addressed by enabling adaptive options for key food security services.
Evidence submitted to the Commons EFRA Committee inquiry by the STFC Food Network+ highlighted that there are currently 48,000 freight operators in the UK, the majority of which are Micro-, Small and Medium-sized Enterprises (MSMEs), with driver shortages being a pre-existing problem for the sector. Regulations around freight operation have been relaxed, such as driver hours and the hours during which deliveries can be made to food retailers. However, a limited ability to be agile in response to shocks is apparent, with distribution centres becoming bottlenecks in the system. Recommendations included the need for the Government to undertake a critical food logistics, distribution and storage review and needs analysis to map and prioritise UK food logistics requirements.
Although disruptions of the global trade in food are minimal so far, trade in agricultural products is projected to contract by the World Trade Organization (WTO) and analysis by the UN Food and Agriculture Organization has suggested that high import dependency could expose countries to COVID-19 disruptions of international supply chains, such as limited capacity due to a lack of personnel at critical connection points for trade. For example, UK food imports are heavily reliant on the Dover Strait maritime route. Higher food prices could also be caused by countries bringing in trade restrictions to safeguard food security, which are amplified by speculation in food commodities in high demand and the financial impacts of pandemic restrictions on companies involved in the food system. The global food system relies heavily on trade to stabilise market prices and avoid price spikes. The UK supplies just over half (53%) of the food consumed in the UK and imports food from over 180 countries, with the leading supplier being the EU (28%). Africa, Asia, North and South America each provided a 4% share of the food consumed in the UK. The three largest value imported commodity groups (at 2018 prices) were fruit and vegetables, meat, and beverages. Importing from more countries provides more potential supply options in case one is disrupted, but for some produce, the UK is highly reliant on a few key countries or regions. For example, 69% of all fresh vegetables imported into the UK are sourced from two EU countries (Spain and the Netherlands). Robustness in supply could be increased by diversifying suppliers across multiple locations; the potential number of suppliers could be increased by encouraging more domestic production of protected and controlled environment vegetable crops, as well as by increasing the number of countries exporting to the UK.
Organisations and researchers continue to debate the role of trade in a resilient food supply. Some commentators have argued the COVID-19 shock has demonstrated how the complex globalised food system has significant adaptive capacity and provides a means to offset a supply chain shock in a given geographic location, but a more complex system creates more degrees of freedom for shocks to occur. For others, shorter local food supply chains are more resilient and long globalised food chains are more vulnerable to regionally-specific supply shocks, and are less transparent. The pandemic has certainly triggered a rise in enquiries from consumers to Community Supported Agriculture schemes, box schemes, independent and alternative food suppliers in the UK, which also reflects positive attitudes and public support for UK-produced food. Efforts have been made to promote transparency in UK supply chains, including through the use of certification schemes. Transparency and integrity in food supply chains extends beyond product certification alone. Without transparency, it is difficult to establish where supply chain problems may be occurring, who will be affected and what policy actions can best promote resilience. However, this remains a challenge due to the complex nature of the global food network, where multiple companies and large geographic distances can be involved in a single supply chain, together with commercial confidentiality constraints. Disruptions can also create potential opportunities for food fraud and food safety breaches. To build resilience, a diversity of approaches and actions taken within the food system may be important (such as taking a combination of actions to boost both local food production, inward investment and international trade).
News of empty supermarket shelves and other disruptions in the food supply chain in countries already affected by COVID-19 influenced UK consumer behaviour and led to relatively short lived ‘stock piling’ buying behaviour to prepare for a worst case scenario. It also led to extensive queues for online delivery of food material from major retailers at the start of lockdown. However, despite this demand shock, there was no demonstrable supply shock in terms of food availability from producers, apart from accessibility constraints for vulnerable groups, food banks and school meals. Defra offered guidance in late April for clinically vulnerable populations, advising this category of citizens to self-isolate and providing them with information regarding their access to food, helplines and shopping guidance and behaviour. This was paired with retailers providing assurances that food supplies would be enough to meet demand.
Other Government measures introduced included easing competition laws to allow collaboration, with retailers able to share stock level data, distribution depots and delivery facilities; relaxing retail drivers hours to allow additional delivery slots to be offered; renewing guidance on best before dates; and the COVID-19 Emergency Surplus Food Grant to address the challenges faced by not-for-profit food redistributors. However, the Commons EFRA Committee has highlighted the increase in demand for food aid from families in financial distress because of the pandemic and the Food and Drink Federation has called for the appointment of a Minister for Hunger. Evidence submitted to the EFRA Committee inquiry by the STFC Food Network+ stated that the Government could incentivise the development of integrated digital platforms and smart food systems for retailers, processors and producers, and government agencies to inform real-time planning and ordering. However, such tools would only be useful if the actors within the food system have the knowledge, capacity, understanding and motivations to use them.
COVID-19 has led to levels of food waste in developed economies increasing from around 30% to 40% of everything that’s produced, distributed and consumed, according to the Global Open Data for Agriculture and Nutrition (GODAN) . This figure includes food surplus and food loss in the supply chain. There was an escalation in food waste immediately after the disruption caused by the closure of the hospitality sector, where shifting surplus to retail has proved difficult given different pack sizes and labelling. The Institute of Food Science and Technology has highlighted that greater intervention could have mitigated the impacts. For example, milk production previously contracted for food service could have been re-directed and processed into butter and skimmed milk powder, both of which have a long shelf life. In evidence to the Commons EFRA Committee, the convening role Defra has played to seek out companies, organisations and initiatives that will help to repurpose goods has been highlighted. However, there have been difficulties for some businesses seeking to re-purpose, such as for millers to sell in small bags to meet consumer demand; or concessions being provided to retail eggs for food service that are not produced to Red Lion standards. The Government put some measures in place to reduce food surplus and food loss, such as financial support for the redistribution of surplus stock, but evidence submitted to EFRA Committee inquiry has questioned whether redistribution approaches are a mitigation option or ‘solution’, both to structural and systematic problems of inequality and normalised overproduction.
Polling has also suggested a change in attitudes to domestic food waste, with households looking to reduce their food waste, with half of the 2000 people polled valuing food more and 48% saying that they are throwing away less food. Of those wasting less, people say they planned meals more carefully (51%) and were getting better at using leftovers (41%). This is achieved through better use of their freezer, with 35% using it more and 29% freezing a wider variety of foods. Portion control is also a factor, with 27% now giving more accurate portion sizes and just 26% leaving less on their plate. The latest survey for the Waste and Resources Action Programme (WRAP) has found that consumers managed their food better in lockdown, and these changed behaviours are leading to a reported 34% reduction in the waste of potatoes, bread, chicken and milk. WRAP has highlighted the need for businesses, local authorities and others to help households make this the ‘new normal’ amid the pressure of time-consuming lifestyles returning.
While the short-term priority has been to stabilise food systems and keep trade open, such crises raise questions about resilience, which is a broader policy issue than just food security, crossing multiple government remits. It is not possible to plan for every potential shock that could affect food security, and planning for the expected, such as preparing for the last crisis, may increase vulnerabilities. The policy instruments needed will be different depending on the phase of the shock, the initial triggers and how elements of government interface and interact to address food security across that timeline. However, crises do expose existing ‘governance gaps’ where the effectiveness of responses to a shock could be improved by clarifying policy responsibilities and having recourse to either a dedicated cross-cutting plan, coordination structure or body. At present no such arrangement to prioritise food exists in England’s food policy-making, which has led to various proposals for new food governance mechanisms in response to COVID-19, including a Minister for Hunger, an independent watchdog and a food aid taskforce. The House of Lords Committee on Food, Poverty, Health and the Environment has recommended creation of a ministerial taskforce and an independent body to provide oversight of all aspects of food policy, including the implementation of the forthcoming National Food Strategy.
At least 16 departments, plus agencies, public bodies and advisory groups, are involved in food policy in England, ranging from Defra to the Department for Business, Energy and Industrial Strategy (BEIS), DHSC and the Department for International Trade (DIT). Evidence submitted to the Commons EFRA Committee inquiry by the University of Hertfordshire has noted several disconnects between departmental remits and activities that have been reiterated by COVID-19. Examples include the potential for better coordination of policy around food provision initiatives, such as school meals, and school milk and fruit and vegetable schemes, where responsibilities cross multiple departments and levels of government. This has resulted in reports of confusion over responsibilities during the pandemic; and the failure to underpin policy interventions with nutrition objectives as embedded in the country’s dietary guidelines. The Faculty of Public Health has also highlighted the need for a clearer voice for public health in UK food system strategy, and noted the need for better links between a robust national level food plan – with health considerations central – and local level development and control, both in relation to COVID-19 and during ‘regular times’. The Local Government Association has also noted how responsibilities between national and local levels require clarification in relation to the COVID-19 response.
A more coordinated or ‘integrated’ approach to food policy would involve joining up goals and activities, and can happen horizontally across government departments, vertically between government levels (for example national and local), and between state and non-state actors. For example, increasing evidence indicates that obesity is an independent risk factor for severe illness and death from COVID-19, the result of creating food environments where it is difficult for communities on low incomes not to survive on calorie-dense foods. However, addressing this will involve joining up the goals of Defra, BEIS, DHSC, Department for Education, Department for Digital, Culture, Media and Sport, Ministry of Housing, Communities and Local Government and DIT. A ‘systems approach’ could be employed to address food security and identify the vulnerabilities, pinch points and resilience that already exist in the food system, such as those approaches that contribute to a more sustainable food supply, lower environmental impacts, transparent supply chains, healthier diets and improved social outcomes. Recognising the elements of food (in)security including access, acquirability and affordability is key in future policy initiatives. Identifying such features requires understanding the system-wide impacts of resilience-building actions and to identify key leverage points. Such actions could involve creating new British Standards geared towards promoting system resilience, enshrining new food system targets into law and periodically reporting progress, and boosting support and funding for projects that encourage greater collaboration between food system actors. A systems approach, which takes account of the coherence and consequences of food-related policy interventions across the rest of the food system, could also ensure actions to address one problem, such as security of food supply, do not create new problems, such as negative environmental impacts either domestically or overseas.
Ben Goodall, Food Standards Agency
Dr Kelly Parsons, University of Hertfordshire
Professor Louise Manning, Royal Agricultural University
Joe Llanos, University of Sheffield
You can find more content from POST on COVID-19 here.
You can find more content on COVID-19 from the Commons and Lords Libraries here.
What can deliberately infecting healthy people tell us about infectious diseases? How is this useful for developing treatments, and how do we manage the risks?
How do our bodies defend against Covid-19? Read how immune responses differ across people, variants, reinfection, vaccination, and current immunisation strategies.
Research studies involving thousands of people have allowed scientists to test which drugs are effective at treating COVID-19. Several drug therapies are now available to treat people who are in hospital with COVID-19, or to prevent infections in vulnerable people becoming more serious. This briefing explains which drugs are available, the groups of people in which they are used and how they work. It also outlines the importance of monitoring the emergence of new variants and drug resistance.