The Reemergent 1977 H1N1 Strain and the Gain-of-Function Debate

In 1978, researchers demonstrated that an H1N1 influenza virus strain from 1950 and another strain from 1977 (Fort Warren [FW] and USSR/90, respectively) were unusually closely related, although they were isolated 27 years apart (4, 6, 7). Using the NCBI Influenza Virus Resource database, we analyzed the hemagglutinin (HA) sequences of all the late 1950s H1N1 strains (1947 to 1957) and compared them to the HA sequences of the 1977 isolates (Table 1). We found that the 1977 cluster has the closest degree of genetic similarity to strains isolated in Albany, NY, in 1948 and 1950, strains isolated in Rome, Italy, in 1949, and strains isolated in Fort Leonard Wood, MO, in 1951, instead of the FW 1950 strain examined previously (Fig. 1). These strains are 98.4% identical (Table 2), containing only four differences among the 566 amino acids that make up the protein, evidence that the 1977 H1N1 epidemic strain is derived from a 1950s virus.

There are historical and epidemiological aspects of the 1977 influenza epidemic that can be considered suspicious. During that time, the Soviet Union employed tens of thousands of scientists to make biological weapons, and as the 1979 release of aerosolized anthrax in Sverdlovsk, Soviet Union, demonstrated, the safety record for the weapons program was not perfect (8). In addition, influenza was considered to be an incapacitating agent, especially to those without previous exposure to a specific virus strain. The lack of immunity to the resurgent strain was clearly evident by the affected population: individuals who were 26 years of age or younger were especially vulnerable to infection. As this is the predominant age range of the active-duty military population, influenza virus could have been used as a biological weapon to target this group.

Indeed, outbreaks of A/USSR/90/77(H1N1) in military academies were described in official memos as “explosive” (9, 10). The Royal Air Force in Upper Heyford, England, was first affected in January 1978, followed by the U.S. Air Force Academy (USAFA) in Colorado in February. The outbreak at the USAFA was so severe—over the course of 9 days, 76%, or 3,280 cadets, became ill—that all academic and military training was suspended. This was the “first such interruption in training due to influenza illness in the cadet population” (9). An epidemiological investigation at USAFA revealed no link to other outbreaks nor a temporal association between the onset of cases and athletic competitions with other institutions with influenza cases. It should be noted, however, that the investigations of illness at military academies were likely better investigated and documented than similar outbreaks at other universities and colleges.

While it is possible that the 1977 influenza was caused by deliberate release of the virus, the Soviet Bioweapons program, Biopreparat, tended to use influenza preparedness as a cover story for some of the more nefarious work that was being performed (11). For example, the Omutninsk Chemical Factory manufactured large amounts of influenza vaccine and crop production bacteria aboveground, while plague and tularemia were researched in heavily guarded underground facilities. The Omutninsk Chemical Factory's capacity to mass produce viruses and bacteria allowed the production of 100 tons of each weapon annually (11). While Biopreparat has not been judged by experts to have seriously investigated influenza as a bioweapon, there were documented attempts to find the 1918 pandemic H1N1 strain in old icehouses where victims were buried, and studies were performed attempting to create radiation-resistant and aerosolized influenza virus (11). Thus, the likelihood of a biological weapons explanation for the 1977 epidemic cannot be completely ruled out, though it may not be considered likely.

There are two factors that point to the 1977 epidemic as resulting from vaccine challenge or trials: (i) live attenuated influenza virus (LAIV) research was extensive at the time, and (ii) a 1976 H1N1 swine flu outbreak was feared to have pandemic potential and led to a resurgent interest in H1N1 protection and research (12).

Between 1962 and 1973, almost 40,000 children participated in eight LAIV trials in the USSR (13). Scientists at the Peking Vaccine and Serum Institute in China also carried out clinical trials using live vaccines during the same time period (1). Additionally, there are records of the mass production of a live H1N1 vaccine in Odessa, USSR, in 1977 (14, 15). In the early days of research in the 1940s, LAIVs were often able to regain virulence upon administration to humans and cause disease (16). In addition, many strains isolated from the 1977 outbreak (for example, the A/Tientsin/78/77 isolate) were temperature sensitive (ts), meaning that the virus could not replicate at higher temperatures. Temperature sensitivity generally occurs only after a series of laboratory manipulations, typical in generation of LAIVs, and is used as a biological marker of attenuation. While not all of the 1977-1978 strains were temperature sensitive, a comparison of all 1977 strains shows a higher prevalence of the ts phenotype than in 1950 strains, supporting the claim that the outbreak may have resulted from attempts at attenuation for vaccine purposes (1, 17). The possibility that the 1977-1978 strain could have resulted from a LAIV trial was also mentioned in a personal communication from C. M. Chu, renowned virologist and the former director of the Chinese Academy of Medical Sciences to Peter Palese, who described “the introduction of this 1977 virus [as] the result of vaccine trials in the Far East involving the challenge of several thousand military recruits with live H1N1 virus” (18). Whether this involved an ineffectively attenuated vaccine or a laboratory-cultivated challenge strain, the deliberate infection of several thousand people with H1N1 would be a plausible spark for the outbreak.

The timing is probably not coincidental. In 1976, the swine H1N1 epizootic influenza virus infected 230 soldiers at Fort Dix, NJ, causing severe respiratory illness in 13 and one death (12). Edwin Kilbourne and others led a campaign that resulted in President Gerald Ford announcing a program to inoculate everyone in the United States against swine flu, and the concomitant production of 150 million doses of influenza vaccine. However, the program was halted soon after, as it became clear that A/New Jersey/1976 was not spreading outside the basic training group. It is possible that an archival H1N1 strain from the early 1950s was used as a challenge virus to evaluate the efficacy of the H1N1 vaccines prepared in response to the 1976 swine flu outbreak. If this virus were not attenuated properly, it may have been able to spread and cause a global epidemic.

A biosafety lapse in a research laboratory is now most often cited as the cause of the 1977-1978 reemergence of the H1N1 influenza virus strain (Fig. 2). The evidence in favor of this possibility is the clear unnatural origin of the virus and its temperature sensitivity, suggesting laboratory manipulations. At the time of the epidemic, however, the World Health Organization excluded the lab accident possibility after discussions with influenza virus laboratory researchers in the Soviet Union and China, finding that “the laboratories concerned either had never kept H1N1 virus or had not worked with it for a long time” (1). It is likely that the swine flu scare the previous year prompted the international community to reexamine their stocks of the latest previously circulating H1N1 strains to attempt to develop a vaccine. However, the tripartite origin of the outbreak in northeast China that produced almost identical isolates is not supportive of the conclusion that this was a single laboratory accident.

It is more likely that either the vaccines produced from these stocks or the viruses themselves used in tests of vaccine development were virulent enough to spark the 1977 epidemic. The bulk of the evidence rests with this possibility: the unnatural origin, mildness of presentation of the virus, widespread dissemination of cases in a short amount of time, temperature sensitivity of the samples, contemporary observations, and existence of live-virus vaccine trials which were occurring at that time.

Explanations for the 1977 epidemic have varied over time and have likely been influenced by political considerations (Fig. 2). In 1991, in the last days of the Soviet Union, researchers suggested that the virus was “potentially frozen” in nature until its reemergence, an unsatisfying explanation that places no blame on China or Russia for the incident (see reference 13 in the Appendix). In 2008, it was suggested that the epidemic was “probably” the result of an influenza vaccine trial (19, 20). The 2009 H1N1 flu (pandemic H1N1/09 virus) brought the 1977 epidemic back to the forefront, as there were soon-discredited rumors that it was the result of a lab accident (21, 22). This reenergized the discussion on the origin of the epidemic, with explanations now “assum[ing] that the virus was kept frozen in a yet unidentified laboratory,” although how it was released was left in doubt (23, 24). However, more-recent publications focusing on the GOF debate have strengthened this stance, concluding that it was “almost certainly due to an escape from a virology lab” (25, 26) (also see references 34 to 41 in the Appendix). Additionally, proponents against GOF research continue to use the potential reemergence from a laboratory accident in their slides and presentations at debates and public forums as a cautionary tale; some examples include the Risks and Benefits of Gain-of-Function Research Symposium held in December 2014, the keynote presentation at the American Biological Safety Association (ABSA) Biological Safety Conference in 2013, and a Viewpoint article published in Nature Reviews Microbiology in December 2014 (27–29).

GOF studies are performed with the aim to better understand disease pathways, but have been controversial because they involve enhancing viral traits, such as pathogenicity or transmissibility, prompting biosafety concerns. Coupled with recent laboratory accidents at the U.S. Centers for Disease Control and Prevention (CDC), the controversy over the potential risks of GOF research led to the recent decision by the U.S. Government to pause federal funding for GOF influenza research and severe acute respiratory syndrome (SARS) research, until an assessment can be made of its risks and benefits (30). The moratorium for MERS and other coronavirus research was lifted, but the evaluation of GOF influenza research risks and benefits is expected to take nearly a year (31, 32).

While the use of the 1977 influenza epidemic as a cautionary tale for potential laboratory accidents is expedient, the relevance to GOF research is greatly diminished if the 1977 epidemic was the result of a vaccine trial or vaccine development gone awry; these are both more plausible explanations than a single laboratory accident. In addition, in 1977, influenza research was performed without modern biosafety regulations and protective equipment, making the lab accident hypothesis much less relevant to the modern GOF debate. While the events that led to the 1977 influenza epidemic cannot preclude a future consequential accident stemming from the laboratory, it remains likely that to this date, there has been no real-world example of a laboratory accident that has led to a global epidemic.