2.48. For rapid response to a pandemic, antiviral
drugs will be the most important weapon available to health services.
Antivirals work by inhibiting the action of particular proteins
on the virus. The four medications available to treat influenza
can be divided into two classes:
- Amantadine and rimantadine, so-called "M2
inhibitors", which probably work by preventing the virus
from entering the host cell;
- Zanamivir (sold as Relenza) and oseltamivir (sold
as Tamiflu), so-called "neuraminidase inhibitors", which
work by blocking the release of the virus from an infected cell.
2.49. These drugs act directly on the virus,
rather than stimulating the production of antibodies. They appear
to be most effective when used prophylacticallythat is,
to prevent infection in those who have been exposed to the virus.
They are also effective in treating the disease, as long as they
are taken within 48 hours of the onset of symptomsthe earlier
the better. If used in this way they can reduce the severity and
duration of symptoms, and reduce the spread of the disease to
others. However, antivirals work only so long as they are being
taken: they confer no long-term immunity, and the protection ceases
as soon as the course is completed. They are not a substitute
2.50. In addition, many of the strains of the
H5N1 avian influenza circulating in south east Asia show signs
of resistance to amantadine. Therefore pandemic preparedness plans
have focused on neuraminidase inhibitors, particularly oseltamivir,
which, as it is available in tablet form, is easily stored and
administered. The Government told us that they were "keeping
a very close eye on" any indication of the emergence of resistance
to oseltamivir. (Q 249)
2.51. Finally, there are simple precautions which
everyone can take to reduce, if not avoid, the risk of infection.
Influenza spreads when an infected person sneezes or coughs. Infection
occurs when droplets are inhaled, or when the virus is picked
up from a contaminated surface and then passed to mouth or nose.
The best way to prevent the spread of influenza is by limiting
the spread of droplets (using a handkerchief, covering the mouth
and nose) and by hand-washing to prevent contamination. The Contingency
Plan, and other Government-issued guidance on pandemic influenza,
explain these simple precautions fully.
2.52. In addition, masks may have some value.
The virus particles are too small to be caught by a normal surgical
or dust mask, and there is no good evidence that the routine wearing
of a mask will protect a wearer from catching influenza. However,
the mask may slightly reduce the risk of an infected person passing
the disease on to others. The mask should be a filtering face-piece
mask, have a good fit and be changed regularly.
4 In addition each of the various H and N antigens
has further subtypes, so that there is, for example, considerable
variety within "N1" neuraminidase antigens. Back
Jeffrey K Taubenberger et al, "Characterization of
the 1918 influenza virus polymerase genes", Nature
437 (5 October 2005), 889-93. Back
Source: WHO (http://www.who.int/csr/disease/avian_influenza/country/en/).
Source: WHO global influenza preparedness plan (http://www.who.int/csr/resources/publications/influenza/WHO_CDS_CSR_GIP_2005_5/en/index.html). Back
Source: Paper presented to WHO conference in Geneva, 7-9 November