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Scientists warn about future flu strains

Governments should start vaccinations against a lethal strain of the influenza virus circulating in birds and pigs, The Independent has reported.

The news is based on an article written by US vaccine researchers, who said that an old flu strain known as H2N2, which caused a pandemic in the 1950s and 60s, could easily start circulating again in humans. The researchers also conducted a small test of 90 people, which showed that people under the age of 50 have little or no immunity to the strain. They argue that creating a new vaccination programme to deal with this strain of flu could save lives by preventing a potential pandemic.

The emergence of different flu strains and the question of whether vaccines are needed against them is an important public health issue, particularly in light of the rapid spread of swine flu in 2009. However, it can be hard to initially tell how widely a new or re-emergent strain of flu will spread or how severely it will affect people. In the case of H2N2, the disease does not currently circulate in humans and any pre-emptive vaccine programme will need further investigation before it can be justified.

 

Where did the story come from?

The report was written by researchers working at the Vaccine Research Centre of the US National Institutes of Health. The researchers did not report any sources of external funding. The report was published in the peer-reviewed journal Nature.

The research article was faithfully reported by both the BBC and The Independent. The BBC included comments from an independent UK expert, who questioned whether the public would want another vaccine against a disease that does not presently exist. The Independent’s headline, which stated that we should “vaccinate against killer flu virus now”, does not reflect the conclusion of the research article, which suggested we should examine the issue rather than begin vaccinations. In addition, it is not possible to tell whether the H2N2 flu virus would be likely to kill if it began circulating in a modern population.

 

What kind of report was this?

This commentary, written by vaccine researchers, argued that government regulatory authorities should plan for a vaccination programme against an old flu strain called H2N2. They warned that this strain is circulating in birds and pigs and could jump to humans, as the H1N1 swine flu strain did in 2009.

In their comment article, the researchers reported details of a small study they conducted, in which they tested 90 US residents for antibodies against the H2N2 flu strain. Their results suggested that people under the age of 50 have little or no immunity to the strain, while resistance dramatically increases in people older than 50. They say this pattern of immunity is similar to that found in H1N1.

 

What does the report say?

The researchers point out that the emergence of a new strain of the H1N1 virus in 2009 took the world by surprise. The public health community had assumed that any future pandemic flu strain would arise from a “major genetic reshuffling” of existing flu viruses to produce a new virus that had never circulated in humans before. As it turned out, the virus that emerged bore a remarkable resemblance to one that had already caused a pandemic 90 years earlier: H1N1 Spanish flu, which killed about 50 million people worldwide. A version of this virus had circulated in pigs for nearly a century and was able to eventually transfer back to humans and cause a new pandemic at a time when immunity levels had waned.

The authors of this comment article say that the unexpected origin of the H1N1 pandemic provides a “cautionary tale” for the public health community, and that the H2N2 strain constitutes a possible public health threat as it could re-emerge in a similar way. They argue that government regulatory agencies should develop a pre-emptive vaccine programme against H2N2.

The researchers draw a number of parallels between the H1N1 and H2N2 viruses. For example, they have both caused pandemics: from 1957 to 1968, an H2N2 strain caused 1–4 million deaths worldwide. Like the 1918 strain, the H2N2 virus has not circulated in humans for several decades but continues to do so among birds and pigs.

To examine people’s levels of immunity to this class of virus, between 2003 and 2007 the researchers tested stored blood samples for antibodies against H2N2 strains in a small cohort of 90 people in the US. The researchers admit that ideally the test needs to be repeated in several thousand individuals, but say their study suggests that people under the age of 50 have little or no immunity to H2N2, and immunity is far stronger in people over 50 (as was also the case for H1N1).

The researchers argue that governments should plan a pre-emptive vaccination programme to prevent the re-emergence of H2N2 in humans, perhaps based on the vaccine against H2N2 licensed for use against the 1957-68 pandemic. They suggest several possible strategies for doing this:

  • Manufacture the vaccine licensed in 1957 and immunise enough of the world’s population to provide “herd immunity” to the rest (i.e. vaccinate a large enough proportion of people so that the virus cannot easily spread to non-vaccinated individuals).
  • Stockpile the vaccine so supplies are ready in the event of an outbreak (which they point out would be more expensive and less effective than routine vaccination).
  • Make “master lots” of H2N2 vaccine and increase production as soon as signs of an outbreak occur (they argue this would be cheaper but less effective than either of the above methods).

 

What do these researchers conclude?

The researchers looked at the pros and cons of developing a pre-pandemic vaccine, including cost, the obstacles to distributing vaccines internationally, potential public distrust of vaccines and the limitations that are placed on public health resources. However, they finally concluded that another major flu pandemic is likely to cost far more and create a far greater health burden than a pre-emptive vaccination programme.  Such a strategy would save lives and “spare the world a major public-health crisis”, they concluded.

 

Conclusion

The researchers raise important questions about the possibility of a future flu pandemic caused by the H2N2 virus, and about whether vaccination programme planning could be used to prevent it. However, many issues need further consideration, including a detailed assessment of the probability of the H2N2 strain jumping to humans, whether it would pose a serious health threat, how long it would take to emerge and which groups of people would be vulnerable. It is important to note that infection with the H1N1 virus, although dangerous for some population groups, did not make most people seriously ill.

As the researchers point out, there are concerns over whether it makes sense to expose individuals to vaccines for a virus that is not currently circulating in humans, although they say the previously licensed H2N2 vaccine has a proven safety and efficacy record. Also, the virus that might emerge in humans may have evolved or mutated to the point where the current H2N2 vaccine no longer provides immunity, although the researchers argue that this is unlikely. As the researchers note, more studies of the existing H2N2 vaccine would be required to confirm its safety and efficacy and to establish who to immunise and when.

The question of whether vaccines should be prepared against the possibility of new, emergent and sometimes dangerous strains of flu is an important public health issue, particularly given the nature of the 2009 swine flu pandemic, in which a new strain of the H1N1 virus emerged and spread quickly.

With new or re-emergent strains of flu, immunity levels are often low, and it can be difficult to initially tell how widely a new strain will spread, or how severely it will affect people. In the case of H2N2, the disease does not currently circulate in humans, so there is still uncertainty over whether it is necessary to plan a vaccine programme and whether existing vaccines would work against an emerging strain. It is also not clear whether the public would find it acceptable to receive or have the government fund a vaccine against a non-circulating disease.

While this research paper rightly argues that an H2N2 vaccination should be investigated, such an examination will need to be informed by evidence on the medical and logistic issues involved, particularly whether available vaccines would be likely to provide protection against future strains.

 

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