Moving beyond metagenomics to find the next pandemic virus

I was asked to write a commentary for the Proceedings of the National Academy of Sciences to accompany an article entitled SARS-like WIV1-CoV poised for human emergence. I’d like to explain why I wrote it and why I spent the last five paragraphs railing against regulating gain-of-function experiments.

Towards the end of 2014 the US government announced a pause of gain-of-function research involving research on influenza virus, SARS virus, and MERS virus that “may be reasonably anticipated to confer attributes to influenza, MERS, or SARS viruses such that the virus would have enhanced pathogenicity and/or transmissibility in mammals via the respiratory route.”

From the start I have opposed the gain-of-function pause. It’s a bad idea fostered by individuals who continue to believe, among other things, that influenza H5N1 virus adapted to transmit by aerosol among ferrets can also infect humans by the same route. Instead of stopping important research, a debate on the merits and risks of gain-of-function experiments should have been conducted while experiments were allowed to proceed.

Towards the end of last year a paper was published a paper on the potential of SARS-virus-like bat coronaviruses to cause human disease. The paper reawakened the debate on the risks and benefits of engineering viruses. Opponents of gain-of-function research began to make incorrect statements about this work. Richard Ebright said that ‘The only impact of this work is the creation, in a lab, of a new, non-natural risk”. Simon Wain-Hobson wrote that a novel virus was created that “grows remarkably well” in human cells; “if the virus escaped, nobody could predict the trajectory”. I have written extensively about why these are other similar statements ignore the value of the work. In my opinion these critics either did not read the paper, or if they did, did not understand it.

Several months later I was asked to write the commentary on a second paper examining the potential of SARS like viruses in bats to cause human disease. I agreed to write it because the science is excellent, the conclusions are important, and it would provide me with another venue for criticizing the gain-of-function pause.

In the PNAS paper, Menachery et al. describe a platform comprising metagenomics data, synthetic virology, transgenic mouse models, and monoclonal antibody therapy to assess the ability of SARS-CoV–like viruses to infect human cells and cause disease in mouse models. The results indicate that a bat SARS-like virus, WIV1-CoV, can infect human cells but is attenuated in mice. Additional changes in the WIV1-CoV genome are likely required to increase the pathogenesis of the virus for mice. The same experimental approaches could be used to examine the potential to infect humans of other animal viruses identified by metagenomics surveys. Unfortunately my commentary is behind a paywall, so for those who cannot read it, I’d like to quote from my final paragraphs on the gain-of-function issue:

The current government pause on these gain-of-function experiments was brought about in part by several vocal critics who feel that the risks of this work outweigh potential benefits. On multiple occasions these individuals have indicated that some of the SARS-CoV work discussed in the Menachery et al. article is of no merit. … These findings provide clear experimental paths for developing monoclonal antibodies and vaccines that could be used should another CoV begin to infect humans. The critics of gain-of-function experiments frequently cite apocalyptic scenarios involving the release of altered viruses and subsequent catastrophic effects on humans. Such statements represent personal opinions that are simply meant to scare the public and push us toward unneeded regulation. Virologists have been manipulating viruses for years—this author was the first to produce, 35 y ago, an infectious DNA clone of an animal virus—and no altered virus has gone on to cause an epidemic in humans. Although there have been recent lapses in high-containment biological facilities, none have resulted in harm, and work has gone on for years in many other facilities without incident. I understand that none of these arguments tell us what will happen in the future, but these are the data that we have to calculate risk, and it appears to be very low. As shown by Menacherry et al. in PNAS, the benefits are considerable.

A major goal of life science research is to improve human health, and prohibiting experiments because they may have some risk is contrary to this goal. Being overly cautious is not without its own risks, as we may not develop the advances needed to not only identify future pandemic viruses and develop methods to prevent and control disease, but to develop a basic understand- ing of pathogenesis that guides prevention. These are just some of the beneficial outcomes that we can predict. There are many examples of how science has progressed in areas that were never anticipated, the so-called serendipity of science. Examples abound, including the discovery of restriction enzymes that helped fuel the biotechnology revolution, and the development of the powerful CRISPR/Cas9 gene-editing technology from its obscure origins as a bacterial defense system.

Banning certain types of potentially risky experiments is short sighted and impedes the potential of science to improve human health. Rather than banning experiments, such as those described by Menachery et al., measures should be put in place to allow their safe conduct. In this way science’s full benefits for society can be realized, unfettered by artificial boundaries.

TWiV 363: Eat flu and dyad

On episode #363 of the science show This Week in Virology, The TWiVers reveal influenza virus replication in the ferret mammary gland and spread to a nursing infant, and selection of transmissible influenza viruses in the soft palate.

You can find TWiV #363 at

Influenza virus in breast milk

Ferret mother-infantDuring breastfeeding, mothers provide the infant with nutrients, beneficial bacteria, and immune protection. Fluids from the infant may also enter the mammary gland through retrograde flux of the nipple. Studies in a ferret model reveal that influenza virus replicates in the mammary gland, is shed in breast milk and transmitted to the infant. Virus may also travel in the opposite direction, from infant to mother.

The role of the mammary gland in influenza virus transmission was studied using a ferret model comprising lactating mothers and nursing infants. Intranasal inoculation of nursing mother ferrets with the 2009 H1N1 influenza virus lead to viral replication and development of influenza in both mother and infant. When the study design was reversed, and 4 week old nursing ferrets were inoculated intranasally with the same virus, viral replication and disease ensued first in the infants, and then in the mothers. Infectious virus was recovered both in the mammary glands and in the nipples at day 4 post infant inoculation, and in mother’s milk from 3-5 days post infant inoculation. Histopathological examination of sections of mammary glands from infected mothers revealed destruction of the mammary architecture.

These results show that nursing infants may pass influenza virus to mothers. It seems clear that influenza virus replicates in the mammary gland and that infectious virus is present in milk. How does this virus infect the mother? One possibility is that infection is transmitted by respiratory contact with virus-containing milk, or by inhalation of aerosols produced by nursing. How influenza virus in the mammary gland would reach the mother’s lung via the blood to cause respiratory disease is more difficult to envision and seems unlikely.

When influenza virus was inoculated into the mammary gland of lactating mothers via the lactiferous ducts, both mother and breast feeding infant developed serious influenza. Infectious virus was detected first in the nasal wash of infants, then later in the nasal wash of mothers. Breast milk contained infectious virus starting on day 2 after inoculation. Histopathological examination of sections from infected mammary glands revealed destruction of glandular architecture and cessation of milk production. This observation is consistent with the results of gene expression analysis of RNA from virus infected mammary glands, which revealed reduction in transcripts of genes associated with milk production.

To determine if human breast cells can be infected with influenza virus, three different human epithelial breast cell lines were infected with the 2009 H1N1 virus strain. Virus-induced cell killing was observed and infectious virus was produced.

Even if we assume that influenza virus can replicate in the human breast, the implications for influenza transmission and disease severity are not clear. Transmission of HIV-1 from mother to infant by breast milk has been well documented. In contrast to influenza virus, HIV-1 is present in the blood from where it spreads to the breast. Most human influenza virus strains do not enter the blood so it seems unlikely that virus would spread to the breast of a mother infected via the respiratory route. However, viral RNA has been detected in the blood of humans infected with the 2009 H1N1 strain, the virus used in these ferret studies. Therefore we cannot rule out the possibility that some strains of influenza virus spread from lung via the blood to the breast, allowing infection of a nursing infant. Some answers might be provided by determining if influenza virus can be detected in the breast milk of humans with influenza.

What would be the implication of a nursing infant infecting the mother’s breast with influenza virus? As I mentioned above, it seems unlikely that this virus would enter the blood, and even if it could, how would the virus infect the apical side of the respiratory epithelium? What does seem clear is that viral replication in the breast could lead to a decrease in milk production which could be detrimental to the infant. If the mother had multiple births, then influenza virus might be transmitted to siblings nursing on the infected mother.

Are you wondering how an infant drinking influenza virus-laded breast milk acquires a respiratory infection? Recently it has been shown that influenza virus replicates in the soft palate of ferrets. The soft palate has mucosal surfaces that face both the oral cavity and the nasopharynx. Ingested virus could first replicate in the soft palate, then spread to the nasopharynx and the lung. A simpler explanation is that nursing produces virus-containing aerosols which are inhaled by the infant.

TWiV 354: The cat in the HAART

On episode #354 of the science show This Week in Virology, the esteemed doctors of TWiV review a new giant virus recovered from the Siberian permafrost, why influenza virus gain of function experiments are valuable, and feline immunodeficiency virus.

You can find TWiV #354 at

1977 H1N1 influenza virus is not relevant to the gain of function debate

The individuals who believe that certain types of gain-of-function experiments should not be done because they are too dangerous (including Lipsitch, Osterholm, Wain-Hobson,) cite the 1977 influenza virus H1N1 strain as an example of a laboratory accident that has led to a global epidemic. A new analysis shows that the reappearance of the 1997 H1N1 virus has little relevance to the gain-of-function debate.

Human influenza viruses of the H3N2 subtype were circulating in May of 1977 when H1N1 viruses were identified in China and then Russia. These viruses spread globally and continue to circulate to this day. The results of serological tests and genetic analysis indicated that these viruses were very similar to viruses of the same subtype which circulated in 1950 (I was in the Palese laboratory in 1977 when these finding emerged). Three hypotheses were suggested to explain the re-emergence of the H1N1 virus: a laboratory accident, deliberate release, or a vaccine trial.

Rozo and Gronvall have re-examined the available evidence for the origin of the 1977 H1N1 virus. While there is ample documentation of the extensive work done during the 1970s in the Soviet Union on biological weapons, there is no evidence that Biopreparat had attempted to weaponize influenza virus. The release of the 1977 H1N1 virus from a biological weapons program is therefore considered unlikely.

It is more likely that the 1977 H1N1 virus was released during testing of influenza virus vaccines. Many such trials were ongoing in the USSR and China during the 1960s-70s. C.M. Chu, a Chinese virologist, told Peter Palese that the H1N1 strain was in fact used in challenge studies of thousands of military recruits, an event which could have initiated the outbreak.

The hypothesis that the 1977 H1N1 virus accidentally escaped from a research laboratory is formally possible, but there are even less data to support this contention. Shortly after this virus emerged, WHO discounted the possibility of a laboratory accident, based on investigations of Soviet and Chinese laboratories. Furthermore, the H1N1 virus was isolated at nearly the same time in three distant areas of China, making release from a single laboratory unlikely.

It is of interest that with the onset of the gain-of-function debate, which began in 2011 with the adaptation of influenza H5N1 virus to aerosol transmission among ferrets, the ‘laboratory accident’ scenario for the emergence of the 1977 strain has been increasingly used as an example of why certain types of experiments are ‘too dangerous’ to be done (See graph, upper left). For example, Wain-Hobson says that ‘1977 H1N1 represented an accidental reintroduction of an old vaccine strain pre-1957, probably from a Russian research lab’. Furmanski writes that ‘The virus may have escaped from a lab attempting to prepare an attenuated H1N1 vaccine’. In the debate on gain-of-function experiments, the laboratory escape hypothesis is prominently featured in public presentations.

The use of an unproven hypothesis to support the view that some research is too dangerous to do is another example of how those opposed to gain-of-function research bend the truth to advance their position. I have previously explained how Lipsitch incorrectly represented the results of the H5N1 ferret transmission studies. We should not be surprised at this tactic. After all, Lipsitch originally called for a debate on the gain-of-function issue, then shortly thereafter declared that the moratorium should be permanent.

Rozo and Gronvall conclude that the use of the 1977 influenza epidemic as a cautionary tale is wrong, because it is more likely that it was the result of a vaccine trial and not a single laboratory accident:

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.

TWiV 336: Brought to you by the letters H, N, P, and Eye

On episode #336 of the science show This Week in Virology, the TWiVsters explore mutations in the interferon pathway associated with severe influenza in a child, outbreaks of avian influenza in North American poultry farms, Ebolavirus infection of the eye weeks after recovery, and Ebolavirus stability on surfaces and in fluids.

You can find TWiV #336 at

How influenza virus infection might lead to gastrointestinal symptoms

influenza virusHuman influenza viruses replicate almost exclusively in the respiratory tract, yet infected individuals may also have gastrointestinal symptoms such as vomiting and diarrhea. In mice, intestinal injury occurs in the absence of viral replication, and is a consequence of viral depletion of the gut microbiota.

Intranasal inoculation of mice with the PR8 strain of influenza virus leads to injury of both the lung and the intestinal tract, the latter accompanied by mild diarrhea. While influenza virus clearly replicates in the lung of infected mice, no replication was observed in the intestinal tract. Therefore injury of the gut takes place in the absence of viral replication.

Replication of influenza virus in the lung of mice was associated with alteration in the populations of bacteria in the intestine. The numbers of segmented filamentous bacteria (SFB) and Lactobacillus/Lactococcus decreased, while numbers of Enterobacteriaceae increased, including E. coli. Depletion of gut bacteria by antibiotic treatment had no effect on virus-induced lung injury, but protected the intestine from damage. Transferring Enterobacteriaceae from virus-infected mice to uninfected animals lead to intestinal injury, as did inoculating mice intragastrically with E. coli.

To understand why influenza virus infection in the lung can alter the gut microbiota, the authors examined immune cells in the gut. They found that Mice lacking the cytokine IL-17A, which is produced by Th17 helper T cells, did not develop intestinal injury after influenza virus infection. However these animals did develop lung injury.

Th17 cells are a type of helper T cells (others include Th1 and Th2 helper T cells) that are important for microbial defenses at epithelial barriers. They achieve this function in part by producing cytokines, including IL-17A. Th17 cells appear to play a role in intestinal injury caused by influenza virus infection of the lung. The number of Th17 cells in the intestine of mice increased after influenza virus infection, but not in the liver or kidney. In addition, giving mice antibody to IL-17A reduced intestinal injury.

There is a relationship between the intestinal microbiome and Th17 cells. In mice treated with antibiotics, there was no increase in the number of Th17 cells in the intestine following influenza virus infection. When gut bacteria from influenza virus-infected mice were transferred into uninfected animals, IL-17A levels increased. This effect was not observed if recipient animals were treated with antibiotics.

A key question is how influenza virus infection in the lung affects the gut microbiota. The chemokine CCL25, produced by intestinal epithelial cells, attracts lymphocytes from the lung to the gut. Production of CCL25 in the intestine increased in influenza virus infected mice, and treating mice with an antibody to this cytokine reduced intestinal injury and blocked the changes in the gut microbiome.

The helper T lymphocytes that are recruited to the intestine by the CCL25 chemokine produce the chemokine receptor called CCR9. These CCR9 positive Th cells increased in number in the lung and intestine of influenza virus infected mice. When helper T cells from virus infected mice were transferred into uninfected animals, they homed to the lung; after virus infection, they were also found in the intestine.

How do CCR9 positive Th cells from the lung influence the gut microbiota? The culprit appears to be interferon gamma, produced by the lung derived Th cells. In mice lacking interferon gamma, virus infection leads to reduced intestinal injury and normal levels of IL-17A. The lung derived CCR9 positive Th cells are responsible for increased numbers of Th17 cells in the gut through the cytokine IL-15.

These results show that influenza virus infection of the lung leads to production of CCR9 positive Th cells, which migrate to the gut. These cells produce interferon gamma, which alters the gut microbiome. Numbers of Th17 cells in the gut increase, leading to intestinal injury. The altered gut microbiome also stimulates IL-15 production which in turn increases Th17 cell numbers.

It has been proposed that all mucosal surfaces are linked by a common, interconnected mucosal immune system. The results presented in this study are consistent with communication between the lung and gut mucosa. Other examples of a common mucosal immune system include the prevention of asthma in mice by the bacterium Helicobacter pylori in the stomach, and vaginal protection against herpes simplex virus type 2 infection conferred by intransal immunization.

Do these results explain the gastrointestinal symptoms that may accompany influenza in humans? The answer is not clear, because influenza PR8 infection of mice is a highly artificial model of infection. It should be possible to sample human intestinal contents and determine if alterations observed in mice in the gut microbiome, Th17 cells, and interferon gamma production are also observed during influenza infection of the lung.

The value of influenza aerosol transmission experiments

ferretA Harvard epidemiologist has been on a crusade to curtail aerosol transmission experiments on avian influenza H5N1 virus because he believes that they are too dangerous and of little value. Recently he has taken his arguments to the Op-Ed pages of the New York Times. While Dr. Lipsitch is certainly entitled to his opinion, his arguments do not support his conclusions.

In early 2013 Lipsitch was the subject of a piece in Harvard Magazine about avian influenza H5N1 virus entitled The Deadliest Virus.  I have previously criticized this article  in which Lipsitch calls for more stringent H5N1 policies. More recently Lipsitch published an opinion in PLoS Medicine in which he called for alternatives to experiments with potential pandemic pathogens. We discussed this piece thoroughly on This Week in Virology #287.  The arguments he uses in both cases are similar to those in the OpEd.

The Times OpEd is entitled Anthrax? That’s not the real worry. The title is a reference to the possible exposure to anthrax bacteria of workers at the Centers for Disease Control. Even worse than anthrax, argues Lipsitch, would be accidental exposure to a pathogen that could transmit readily among humans. He then argues that such a pathogen is being created in laboratories that study avian influenza H5N1 transmission.

Lipsitch tells us ‘These experiments use flu strains like H5N1, which kills up to 60 percent of humans who catch it from birds.’ As an epidemiologist Lipsitch knows that this statement is wrong. The case fatality ratio for avian H5N1 influenza virus in humans is 60% – the number of deaths divided by the cases of human infections that are diagnosed according to WHO criteria. The mortality rate is quite different: it is the number of fatalities divided by the total number of H5N1 infections of humans. For a number of reasons the H5N1 mortality ratio in humans has been a difficult number to determine.

Next Lipsitch incorrectly states that the goal of experiments in which avian influenza H5N1 viruses are given the ability to transmit by aerosol among ferrets is ‘to see what gives a flu virus the potential to create a pandemic.’ The goal of these experiments is to identify mechanistically what is needed to make an avian influenza virus transmit among mammals. Transmission of a virus is required for a pandemic, but by no means does it assure one. I do hope that Lipsitch knows better, and is simply trying to scare the readers.

He then turns to the experiments of Kawaoka and colleagues who recently reconstructed a 1918-like avian influenza virus and provided it with the ability to transmit by aerosol among ferrets. These experiments are inaccurately described. Lipsitch writes that the reconstructed virus was ‘both contagious and comparably deadly to the 1918 flu that killed tens of millions of people worldwide’. In fact the reconstructed virus is less virulent in ferrets than the 1918 H1N1 virus that infected humans. In the same sentence Lipsitch mixes virulence in ferrets with virulence in humans – something even my virology students know is wrong. Then he writes that ‘Unlike experiments with anthrax, creating such flu strains in the lab presents a danger that affects us all, because once it is out, such a strain would be extremely hard to control.’ This is not true for the 1918-like avian influenza virus assembled by the Kawaoka lab: it was shown that antibodies to the 2009 pandemic H1N1 influenza virus can block its replication. The current influenza virus vaccine contains a 2009 H1N1 component that would protect against the 1918-like avian influenza virus.

The crux of the problem seems to be that Lipsitch does not understand the purpose of influenza virus transmission experiments. He writes that ‘The virologists conducting these experiments say that by learning about how flu transmits in ferrets, we will be able to develop better vaccines and spot dangerous strains in birds before they become pandemic threats.’ This justification for the work is wrong.

Both Kawaoka and Fouchier have suggested that identifying mutations that improve aerosol transmission of avian influenza viruses in ferrets might help to detect strains with transmission potential, and help vaccine manufacture. I think it was an error to focus on these potential benefits because it detracted from the real value of the work, to provide mechanistic information on what allows aerosol transmission of influenza viruses among mammals.

In the Kawaoka and Fouchier studies, it was found that adaptation of H5N1 influenza virus from avian to mammalian receptors lead to a decrease in the stability of the viral HA glycoprotein. This property had to be reversed in order for these viruses to transmit by aerosol among ferrets. Similar stabilization of the HA protein was observed when the reconstructed 1918-like avian influenza virus was adapted to aerosol transmission among ferrets. It is not simply coincidence when three independent studies come up with the same outcome: clearly HA stability is important for aerosol transmission among mammals. This is one property to look for in circulating H5N1 strains, not simply amino acid changes.

Lipsitch mentions nothing about the mechanism of transmission; he focuses on identifying mutations for surveillance and vaccine development. He ignores the fundamental importance of this work. In this context, the work has tremendous value.

The remainder of the Times OpEd reminds us how often accidents occur in high security biological labortories. There are problems with these arguments. Lipsitch cites the emergence of an H1N1 influenza virus in 1977 as ‘escaped from a lab in China or the Soviet Union’. While is seems clear that the 1977 H1N1 virus probably came from a laboratory, there is zero evidence that it was a laboratory accident. It is equally likely that the virus was part of a clinical trial in which it was deliberately administered to humans.

Lipsitch also cites the numerous incidents that occur in American laboratories involving select agents. I suggest the reader listen to Ron Fouchier explain on TWiV #291 how a computer crash must be recorded as an incident in high biosecurity laboratories, but does not lead to the release of infectious agents.

Lipsitch clearly feels that the benefits of aerosol transmission research do not justify the risks involved. I agree that the experiments do have some risk, but it is not as clear cut as Lipsitch would suggest. Although ferrets are a good model for influenza virus pathogenesis, like any animal model, they are not predictive of what occurs in humans. An influenza virus that transmits by aerosol among ferrets cannot be assumed to transmit in the same way among humans. This is the assumption made by Lipsitch, and it is wrong.

I agree that transmission work on avian H5N1 influenza virus must be done under the proper containment. Before these experiments can be done they are subject to extensive review of the proposed containment and mitigation procedures. There is no justification for the additional regulation proposed by Lipsitch.

In my opinion aerosol transmission experiments on avian influenza viruses are well worth the risk. We know nothing about what controls aerosol transmission of viruses. The way to obtain this information is to take a virus that does not transmit by aerosol, derive a transmissible version, and determine why the virus has this new property. To conclude that such experiments are not worth the risk not only ignores the importance of understanding transmission, but also fails to acknowledge the unpredictable nature of science. Often the best experimental results are those which were never anticipated.

Lipsitch ends by saying that ‘There are dozens of safe research strategies to understand, prevent and treat pandemic flu. Only one strategy — creating virulent, contagious strains — risks inciting such a pandemic.’ Creating a virulent strain is not part of the strategy. Lipsitch conveniently ignores the fact that Fouchier’s H5N1 strain that transmits by aerosol among ferrets is not virulent when transmitted by that route. And of course we do not know if these strains would be transmissible in humans.

I am very disappointed that the Times chose to publish this OpEd without checking Lipsitch’s statements. He is certainly entitled to his own opinion, but he is not entitled to his own facts.

Unusual mortality pattern of 1918 influenza A virus

1918 influenza mortalityThe 1918 influenza pandemic was particularly lethal, not only for the very young and the very old (as observed for typical influenza), but unexpectedly also for young adults, 20 to 40 years of age (pictured). It has been suggested that the increased lethality in young adults occurred because they lacked protective immunity that would be conferred by previous infection with a related virus. Reconstruction of the origins of the 1918 influenza virus provides support for this hypothesis.

Analysis of influenza virus genome sequences using a host-specific molecular clock together with seroarchaeology (analysis of stored sera for the presence of antibodies to influenza virus) indicates that the 1918 H1N1 virus arose ~1915 by reassortment of an avian influenza virus with an H1 virus that had previously emerged around 1907. The 1918 virus acquired the HA gene from the 1907 virus, and the NA gene and internal protein genes from an avian virus. This 1918 virus also infected pigs, in which descendants continue to circulate; however the human 1918 virus was displaced in 1922 by a reassortant with a distinct HA gene.

Seroarchaeology and mortality data indicate that an influenza pandemic in 1889-1893 was caused by an influenza H3N8 virus. This virus appears to have circulated until 1900, when it was replaced by a H1N8 virus (the N8 gene originating from the previously circulating H3N8 virus).

How do these events explain the unusual mortality pattern of the 1918 influenza A virus? High mortality among 20-40 year old adults might have been a consequence of their exposure to the H3N8 virus that circulated from 1889-1900. This infection provided no protection against the 1918 H1N1 virus. Protection of other age groups from lethal infection was likely a consequence of childhood exposure to N1 or H1 containing viruses (this may also have resulted in the lower than usual mortality in the elderly population). Influenza is typically highly lethal in very young children due to lack of immunologic memory.

These observations suggest that childhood exposure to influenza virus is a key predictor of virulence of a pandemic strain. Antibodies against the stalk of the HA protein protect against severe disease, but only within groups of HA subtypes (HA groups are determined by phylogenetic analysis). In 1918, antibodies against a group 2 HA subtype virus (H3) did not protect against severe disease caused by a group 1 HA subtype virus (H1). Childhood exposure might also determine mortality of seasonal influenza. For example, the high virulence of currently circulating H3N2 influenza viruses in those older than 65 years might be a consequence of infection with an H1N1 virus at a young age.

This logic can also explain mortality caused by influenza H5N1 and H7N9 viruses. Most fatalities caused by H5N1 viruses (the H5 is a group 1 HA) have been in individuals who were infected as children with an H3 virus (group 2 HA). Most fatalities caused by H7N9 viruses (group 2 HA) have occurred in individuals who were infected as children with H1N1 or H2N2 viruses (group 1 HA).

The practical consequence of this work are clearly stated by the authors:

Immunization strategies that mimic the apparently powerful lifetime protection afforded by initial childhood exposure might dramatically reduce mortality due to both seasonal and novel IAV strains.

TWiV 282: Tamiflu and tenure too

On episode #282 of the science show This Week in Virology, the TWiV team reviews a meta-analysis of clinical trial reports on using Tamiflu for influenza, and suggestions on how to rescue US biomedical research from its systemic flaws.

You can find TWiV #282 at