A Brief History of Human Challenge Studies (1900-2021) Emphasising the Virology, Regulatory and Ethical Requirements, Raison D'etre, Ethnography, Selection of Volunteers and Unit Design.

Venetian quarantine 400 years ago was an important public health measure. Since 1900 this has been refined to include "challenge" or deliberate infection with pathogens be they viruses, bacteria, or parasites. Our focus is virology and ranges from the early experiments in Cuba with Yellow Fever Virus to the most widespread pathogen of our current times, COVID-19. The latter has so far caused over four million deaths worldwide and 190 million cases of the disease. Quarantine and challenge were also used to investigate the Spanish Influenza of 1918 which caused over 100 million deaths. We consider here the merits of the approach, that is the speeding up of knowledge in a practical sense leading to the more rapid licensing of vaccines and antimicrobials. At the core of quarantine and challenge initiatives is the design of the unit to allow safe confinement of the pathogen and protection of the staff. Most important though is the safety of volunteers. We can see now, as in 1900, that members of our society are prepared and willing to engage in these experiments for the public good. Our ethnology study, where the investigator observed the experiment from within the quarantine, gave us the first indication of changing attitudes amongst volunteers whilst in quarantine. These quarantine experiments, referred to as challenge studies, human infection studies, or "controlled human infection models" involve thousands of clinical samples taken over two to three weeks and can provide a wealth of immunological and molecular data on the infection itself and could allow the discovery of new targets for vaccines and therapeutics. The Yellow Fever studies from 121 years ago gave the impetus for development of a successful vaccine still used today whilst also uncovering the nature of the Yellow Fever agent, namely that it was a virus. We outline how carefully these experiments are approached and the necessity to have high quality units with self-contained air-flow along with extensive personal protective equipment for nursing and medical staff. Most important is the employment of highly trained scientific, medical and nursing staff. We face a future of emerging pathogens driven by the increasing global population, deforestation, climate change, antibiotic resistance and increased global travel. These emerging pathogens may be pathogens we currently are not aware of or have not caused outbreaks historically but could also be mutated forms of known pathogens including viruses such as influenza (H7N9, H5N1 etc.) and coronaviruses. This calls for challenge studies to be part of future pandemic preparedness as an additional tool to assist with the rapid development of broad-spectrum antimicrobials, immunomodulators and new vaccines.

The end of the beginning: vaccines for the next 25 years.

The first virus vaccines against smallpox and rabies proved their effectiveness even before the ultra microscopic viruses had been identified as a new world of infectious agents. To date most antibacterial and antiviral vaccines have not been designed but rather built step by step. Designer vaccines with T cell epitopes and adjuvants which stimulate innate or acquired immune responses to will are now under serious investigation but have yet to impact on the practical world of infection. The latter is not small, with millions of deaths annually in the world from not uncommon microbes such as enterforms, pneumococci, respiratory and hepatitis viruses and HIV. But can vaccines be used in more social directions to control birth or prevent addiction? Polio should join smallpox this year in the pantheon of eradicated viruses. The infectious disease community can then turn attention to hepatitis B. War has been declared on pandemic influenza but with this zoonotic virus containment is key, with vaccines used alongside antivirals and social distancing. Undoubtedly "we have the guns, and now we can finish the job".

Scientific lessons from the first influenza pandemic of the 20th century.

Re-analysis of the influenza pandemic of 1918 has given reassurance about a rather low reproductive number (R(o)), a prolonged herald wave of virus and that the skewed mortality towards the young adult could be a singularly unique event dependent upon previous infection history, perhaps not to be repeated in a future pandemic. Over 99% of those who contracted the virus survived, in spite of the absence of antivirals, vaccine and antibiotics for the secondary bacteria infections which probably accounted for one-third of the 50 million deaths. Therefore, in spite of a three-fold population increase since 1918 and 100 thousand plane journeys daily, judicious and careful planning together with a stockpile of antiviral drugs, oseltamivir, zanamivir and M2 blockers and a generic H5N1 vaccine, and application of hygiene would be expected to reduce mortality in a new pandemic, to figures significantly less than 1918.

Interfering vaccine (defective interfering influenza A virus) protects ferrets from influenza, and allows them to develop solid immunity to reinfection.

Defective interfering (DI) virus RNAs result from major deletions in full-length viral RNAs that occur spontaneously during de novo RNA synthesis. These RNAs are packaged into virions that are by definition non-infectious, and are delivered to cells normally targeted by the virion. DI RNAs can only replicate with the aid of a coinfecting infectious helper virus, but the small size of DI RNA allows more copies of it to be made than of its full-length counterpart, so the cell produces defective virions in place of infectious progeny. In line with this scenario, the expected lethal disease in an influenza A virus-mouse model is made subclinical by administration of DI virus, but animals develop solid immunity to the infecting virus. Hence DI virus has been called an 'interfering vaccine'. Because interfering vaccine acts intracellularly and at a molecular level, it should be effective against all influenza A viruses regardless of subtype. Here we have used the ferret, widely acknowledged as the best model for human influenza. We show that an interfering vaccine with defective RNAs from an H3N8 virus almost completely abolished clinical disease caused by A/Sydney/5/97 (H3N2), with abrogation of fever and significant reductions in clinical signs of illness. Animals recovered fully and were solidly immune to reinfection, in line with the view that treatment converts the otherwise virulent disease into a subclinical and immunizing infection.

Influenza is now a preventable disease.

The world is waiting with apprehension for the predicted pandemic of H5N1 (avian) influenza as an increasing number of countries in Asia, Europe and Africa report cases of influenza in migrating birds. All is not 'despondency', however. Targeted and controlled administration of antiviral drugs, alone or in combination, to contacts and cases, together with well tried public health measures, should slow down the spread of the infection and allow time for vaccines to be developed, thus preventing a worldwide pandemic of the type that occurred in 1918.

A new European perspective of influenza pandemic planning with a particular focus on the role of mammalian cell culture vaccines.

Sixteen EU scientists and doctors were interviewed about pandemic planning using psychometric methods applied to a scientific problem for the first time. Criticism was aimed at countries which have no plan whatsoever, the majority of nations. Many such countries have not invested in scientific infrastructure and public health. Amongst the 15 or so published pandemic plans a lack of detail was identified. Of particular need was investment into avian virus vaccine stocks (H1-15), prepared licenses of vaccine and pre purchase and agreed distribution, investment into stocks of antivirals, antibiotics and masks. Most but not all members of the group predicted a global outbreak within 5 years, most probably starting in SE Asia. However it was recognised that a pandemic could start anywhere in the world which had juxtaposition of young people, chickens, ducks and pigs. Mammalian cell culture production using wild type virus with the production factory at category III levels of security was exemplified. Antivirals would be essential to ameliorate the first wave of infection although significant quantities of cell grown vaccine could be produced if, as in 1918, 1957 and 1968 there is a long period between the first virus isolation and person to person spread. The wider scientific community is more energised than previously for very serious preparations to be in place way before the outbreak begins as this is a major public health problem, completely dwarfing concerns about bioterrorism.

A hypothesis: the conjunction of soldiers, gas, pigs, ducks, geese and horses in northern France during the Great War provided the conditions for the emergence of the "Spanish" influenza pandemic of 1918-1919.

The Great Influenza Pandemic of 1918-1919 was a cataclysmic outbreak of infection wherein over 50 million people died worldwide within 18 months. The question of the origin is important because most influenza surveillance at present is focussed on S.E. Asia. Two later pandemic viruses in 1957 and 1968 arose in this region. However we present evidence that early outbreaks of a new disease with rapid onset and spreadability, high mortality in young soldiers in the British base camp at Etaples in Northern France in the winter of 1917 is, at least to date, the most likely focus of origin of the pandemic. Pathologists working at Etaples and Aldershot barracks later agreed that these early outbreaks in army camps were the same disease as the infection wave of influenza in 1918. The Etaples camp had the necessary mixture of factors for emergence of pandemic influenza including overcrowding (with 100,000 soldiers daily changing), live pigs, and nearby live geese, duck and chicken markets, horses and an additional factor 24 gases (some of them mutagenic) used in large 100 ton quantities to contaminate soldiers and the landscape. The final trigger for the ensuing pandemic was the return of millions of soldiers to their homelands around the entire world in the autumn of 1918.

Lack of detection of influenza genes in archived formalin-fixed, paraffin wax-embedded brain samples of encephalitis lethargica patients from 1916 to 1920.

A method was developed for detection of influenza genes in formalin-fixed brains of mice that had been experimentally infected with influenza A/NWS/33 (H1N1) virus. Using this technique, messenger ribonucleic acid (mRNA) of the beta-actin gene was detected in eight clinical brain samples from the 1916-1920 outbreak of encephalitis lethargica, showing preservation of particular mRNAs. However, we did not detect influenza nucleotide sequences of M, NP, and NS genes from these same samples. We conclude either that influenza was not the causative agent of encephalitis lethargica or, possibly, that the virus had a hit-and-run mechanism and was no longer present in the brain at the time of death of the patients.

Treatment of epidemic and pandemic influenza with neuraminidase and M2 proton channel inhibitors.

A small armentarium of anti-influenza drugs now exists, and includes the M2 blockers (amantadine and rimantadine) and the neuraminidase inhibitors (Relenza and Tamiflu). The neuraminidase inhibitors have certain advantages, including a broader spectrum of antiviral activity, including influenza A and B viruses. On the other hand, there is now much clinical experience with the M2 blockers, and these drugs are inexpensive. It is clear that influenza in different community groups needs to be managed in specific and targeted ways. For example, in the over-65-years and at-risk groups, vaccination will remain a mainstay of disease prevention. However, up to 40% of those in these groups may fail to receive vaccine, and therefore the antivirals can be used therapeutically, or, in defined circumstances, as prophylactics. At present, influenza is hardly managed in the community. The infrequent global outbreaks, pandemics, present further problems. The more extensive use of the two classes of antivirals, and also vaccines, in the important interpandemic years will provide a very significant investment in health benefits in the face of a new pandemic virus in an otherwise completely vulnerable population.

A designer drug against influenza: the NA inhibitor oseltamivir (Tamiflu).

The description of the first two designer antiviral drugs to fight influenza was a ground breaking advance. Targeted against the influenza neuraminidase enzyme these inhibitors have been shown to reduce both the severity and duration of influenza illness. Importantly, it is expected that these neuraminidase inhibitors would be effective against influenza pandemic strain and could therefore be vital at reducing the potentially devastating consequences of such an outbreak. Despite the demonstrated efficacy of these drugs, they are not commonly used, particularly in the UK, and there is substantial concern that in the event of a pandemic or even a severe epidemic there could be substantial morbidity and mortality. SARS has shown that the public and media response to a serious epidemic is not always rational and this could easily become panic if it became apparent that treatment was possible, but not available.

The H274Y mutation in the influenza A/H1N1 neuraminidase active site following oseltamivir phosphate treatment leave virus severely compromised both in vitro and in vivo.

Oseltamivir carboxylate is a potent and specific inhibitor of influenza A and B neuraminidase (NA). Oseltamivir phosphate, the ethyl ester prodrug of oseltamivir carboxylate, is the first orally active NA inhibitor available for the prophylaxis and treatment of influenza A and B. It offers an improvement over amantadine and rimantadine which are active only against influenza A and rapidly generate resistant virus. The emergence of virus resistant to oseltamivir carboxylate in the treatment of naturally acquired influenza infection is low (about 1%). The types of NA mutation to arise are sub-type specific and largely predicted from in vitro drug selection studies. A substitution of the conserved histidine at position 274 for tyrosine in the NA active site has been selected via site directed mutagenesis, serial passage in culture under drug pressure in H1N1 and during the treatment of experimental H1N1 infection in man. Virus carrying H274Y NA enzyme selected in vivo has reduced sensitivity to oseltamivir carboxylate. The replicative ability in cell culture was reduced up to 3 logs, as was infectivity in animal models of influenza virus infection. Additionally, pathogenicity of the mutant virus is significantly compromised in ferret, compared to the corresponding wild type virus. Virus carrying a H274Y mutation is unlikely to be of clinical consequence in man.

World War I may have allowed the emergence of "Spanish" influenza.

The 1918 influenza pandemic caused 40 million deaths, and so dwarfed in mortality and morbidity the preceding pandemic of 1889 and the 1957 and 1968 pandemics. In retrospect, much can be learnt about the source, the possible subterranean spread of virus, and the genetic basis of virulence. The World Health Organization has urged every nation to prepare a pandemic plan for the first global outbreak of the 21st century. We present an appraisal of epidemiological and mortality evidence of early outbreaks of respiratory disease in France and the UK in the years 1915 to 1917. Certain of these earlier focal outbreaks--called epidemic bronchitis rather than influenza--occurred during the winter months when influenza was known to be in circulation, and presented with a particular heliotrope cyanosis that was so prominent in the clinical diagnosis in the world pandemic outbreak of 1918-1919 (the Great Pandemic). The outbreaks in army camps at Etaples in France and Aldershot in the UK in 1916-1917 caused very high mortality in 25-35 year olds. Increased deaths from bronchopneumonia and influenza were also recorded in England. We deduce that early focal outbreaks of influenza-like disease occurred in Europe and on the balance of probability the Great Pandemic was not initiated in Spain in 1918 but in another European country in the winter of 1916 or 1917. We suggest that the pandemic had its origins on the Western Front, and that World War I was a contributor.

Effectiveness of oseltamivir in preventing influenza in household contacts: a randomized controlled trial.

CONTEXT: Influenza virus is easily spread among the household contacts of an infected person, and prevention of influenza in household contacts can control spread of influenza in the community. OBJECTIVE: To investigate the efficacy of oseltamivir in preventing spread of influenza to household contacts of influenza-infected index cases (ICs). DESIGN AND SETTING: Randomized, double-blind, placebo-controlled study conducted at 76 centers in North America and Europe during the winter of 1998-1999. PARTICIPANTS: Three hundred seventy-seven ICs, 163 (43%) of whom had laboratory-confirmed influenza infection, and 955 household contacts (aged >/=12 years) of all ICs (415 contacts of influenza-positive ICs). INTERVENTIONS: Household contacts were randomly assigned by household cluster to take 75 mg of oseltamivir (n = 493) or placebo (n = 462) once daily for 7 days within 48 hours of symptom onset in the IC. The ICs did not receive antiviral treatment. MAIN OUTCOME MEASURE: Clinical influenza in contacts of influenza-positive ICs, confirmed in a laboratory by detection of virus shedding in nose and throat swabs or a 4-fold or greater increase in influenza-specific serum antibody titer between baseline and convalescent serum samples. RESULTS: In contacts of an influenza-positive IC, the overall protective efficacy of oseltamivir against clinical influenza was 89% for individuals (95% confidence interval [CI], 67%-97%; P<.001) and 84% for households (95% CI, 49%-95%; P<.001). In contacts of all ICs, oseltamivir also significantly reduced incidence of clinical influenza, with 89% protective efficacy (95% CI, 71%-96%; P<.001). Viral shedding was inhibited in contacts taking oseltamivir, with 84% protective efficacy (95% CI, 57%-95%; P<.001). All virus isolates from oseltamivir recipients retained sensitivity to the active metabolite. Oseltamivir was well tolerated; gastrointestinal tract effects were reported with similar frequency in oseltamivir (9.3%) and placebo (7.2%) recipients. CONCLUSION: In our sample, postexposure prophylaxis with oseltamivir, 75 mg once daily for 7 days, protected close contacts of influenza-infected persons against influenza illness, prevented outbreaks within households, and was well tolerated.

The so-called Great Spanish Influenza Pandemic of 1918 may have originated in France in 1916.

This discussion piece examines the likely epicentre of the influenza pandemic of 1918-1919. Contrary to previous studies that have proposed a Chinese origin, there is documentation that suggests that, in this instance, the virus spread eastwards to China from Europe. Although more recent oubreaks of influenza have undoubtedly had an Oriental origin, the evidence indicates that future outbreaks could conceivably arise anywhere in the world.

Influenza virus infection in the second and third trimesters of pregnancy: a clinical and seroepidemiological study.

OBJECTIVE: To determine whether maternal influenza virus infection in the second and third trimesters of pregnancy results in transplacental transmission of infection, maternal auto-antibody production or an increase in complications of pregnancy. DESIGN: Case-control cohort study. POPULATION: Study and control cohorts were derived from 3,975 women who were consecutively delivered at two Nottingham teaching hospitals between May 1993 and July 1994. A complete set of three sera was available for 1,659 women. METHODS: Paired maternal ante- and postnatal sera were screened for a rise in anti-influenza virus antibody titre by single radial haemolysis and haemagglutination inhibition. Routine obstetric data collected during and after pregnancy were retrieved from the Nottingham obstetric database. Cord samples were tested for the presence of IgM anti-influenza antibodies, and postnatal infant sera were tested for the persistence of influenza-virus specific IgG. Paired antenatal and postnatal sera were tested against a standard range of auto-antigens by immunofluorescence. MAIN OUTCOME MEASURES: Classification of women as having definite serological evidence of an influenza virus infection in pregnancy (cases) or as controls. RESULTS: Intercurrent influenza virus infections were identified in 182/1,659 (11.0%) pregnancies. None of 138 cord sera from maternal influenza cases was positive for influenza A virus specific IgM. IgG anti-influenza antibodies did not persist in any of 12 infant sera taken at age 6-12 months. Six of 172 postnatal maternal sera from cases of influenza were positive for auto-antibodies. In all cases the corresponding antenatal serum was also positive for the same auto-antibody. There were no significant differences in pregnancy outcome measures between cases and controls. Overall, there were significantly more complications of pregnancy in the cases versus the controls, but no single type of complication achieved statistical significance. CONCLUSIONS: Influenza infection in the second and third trimesters of pregnancy is a relatively common event. We found no evidence for transplacental transmission of influenza virus or auto-antibody production in pregnancies complicated by influenza infections. There was an increase in the complications of pregnancy in our influenza cohort.

In vitro anti-HIV-1 virucidal activity of tyrosine-conjugated tri- and dihydroxy bile salt derivatives.

The cellular toxicity and anti-human immunodeficiency virus type 1 (HIV-1) virucidal activity of four synthesized tyrosine-conjugated bile salt derivatives with high surfactant activities, namely di-iodo-deoxycholyltyrosine (DIDCT), di-iodo-chenodeoxycholyltyrosine (DICDCT), di-iodo-cholylglycyltyrosine (DICGT) and deoxycholyltyrosine (DCT), were evaluated and compared with either sodium deoxycholate or nonoxynol-9. DIDCT, DICDCT and DCT but not DICGT showed virucidal activity against three different laboratory-adapted strains of HIV-1 (RF, IIIB and MN). All the bile salt derivatives tested excluding DICGT were virucidal at a concentration as low as 10 ng/mL. DCT had the highest anti-HIV-1 virucidal potency, suggesting that monopeptide 7alpha,12alpha dihydroxy bile salt derivatives have the most potent antiviral activity. Complexing of iodine to the bile salt derivative (as in DICGT) decreases virucidal potency.

Rapid antibody response to influenza vaccination in "at risk" groups.

Persons attending for routine influenza vaccination in an urban practice each provided three specimens of blood for evaluating their immunological response. 138 (67%) of the 206 persons were defined as "at risk" by reason of morbidity as given in the guidelines published by the Chief Medical Officer. The mean age was 67 yr and 65% were aged 65 yr or more. By day 7, 71% of 31 persons had protective H(1)N(1) titres, 61% H(3)N(2) and 42% B. These proportions were similar to those found at day 14 and at day 21 based on 159 persons. These findings suggest that an effective immune response is mounted within seven days of vaccination indicating that the vaccination of persons "at risk" is worthwhile even after an epidemic has established itself. This is not a reason to modify present policy of routine vaccination in early winter well before epidemics are likely to occur.

Influenza A pandemics of the 20th century with special reference to 1918: virology, pathology and epidemiology.

Influenza A virus initiated worldwide epidemics (pandemics) in 1918, 1957, 1968 and 1977. A revised calculation of the 1918-1919 pandemic estimates that 40 million persons died and 500 million were infected. The mortalities in 1957 and 1968 were nearly 6 million. Biological and genetic characteristics of the causative agents of the more recent pandemics, have been well studied but little is known about the causative agent of the Great Pandemic in 1918. Genetic characterisation of the 1918 virus has been achieved by sourcing virus RNA from formalin fixed lung samples or by exhuming frozen victims of the outbreak from Arctic regions. Initial analysis of the HA gene from two USA sources indicates a virus related to swine and human influenza with no base insertion at the HA1-HA2 cleavage junction which, at least in avian influenza A, characterises high virulence. Important unanswered questions are whether the 1918 virus spread pantropically perhaps to include the brain and hence cause encephalitis including the later lethargic forms, or whether infection was confined to the respiratory tract. Re-examination of reports of respiratory disease in England and France in 1916-1917 may indicate a non-Spanish origin of the pandemic and a period of 2 years for the virus to be seeded worldwide. In contrast the other two pandemic viruses in 1957 and 1968 appeared to originate in Asia. New anti-neuraminidase drugs in conjunction with amantadine and novel developments with influenza vaccines would be expected to ameliorate the disease in a future pandemic.