Pinning and tackling swine flu

VIRUS WATCH: The influenza viruses are slippery viruses. Each strain of a virus can undergo a ‘drift’ in which genetic mutations can occur,resulting in the emergence of immunologically distinct variants. This has implications for the vaccine virus composition. Such genetic mutations arise frequently in the flu viruses,requiring a periodic review and revision of the flu vaccine antigens.

The greater danger,however,is an ‘antigenic shift’ when one flu virus strain consorts with another flu virus strain and undergoes a ‘reassortment’ of antigens,with a change in the genetic composition. Flu viruses are notoriously promiscuous and the resultant reassortment may produce a more virulent strain.

The behaviour of the H1N1 virus in India,as well as elsewhere in the world,needs to be watched over the next six months. This is especially important when the seasonal flu viruses get active by October.

VACCINE WATCH: Vaccination provides substantial protection against influenza in healthy and at-risk individuals. Efficacy ranges from 26 per cent to 87 per cent depending on the vaccine match (with the viruses circulating at that time) and age of the individual. Current projections for the availability of an H1N1 vaccine in India range from 3-6 months. Gene mutations will pose challenges but newer technologies can,to some extent,help overcome these ‘drift’ variants. Several regulatory and production steps are needed to ensure the availability of a safe and effective vaccine in adequate quantity,before a vaccine can be released for general use. Because of antigen variability,a vaccination strategy alone may not be sufficient to control pandemic influenza.

DRUG WATCH: The anti-viral drugs available are oseltamivir (popularised by its leading brand name Tamiflu) and zanamivir. These neuraminidase inhibitors have been evaluated in trials of seasonal flu caused by other strains but trials against H1N1 virus have not been reported. Systematic reviews of these trials,recently published in the Lancet and the British Medical Journal,do not reveal a demonstrable benefit on the occurrence of asthma,use of antibiotics or serious complications. The fatality rates of seasonal flu being low in general,much larger studies would be needed to examine whether these drugs reduce mortality but it is unlikely that they do so in a substantial measure. Since the present ‘Swine flu’ virus is also a mild one (as virulence grades of viruses go),these trial results would appear applicable to it as well.

Despite no clear evidence of benefit in flu patients with co-existing health conditions,as compared to healthy persons who have been infected,there may be a clinical rationale in prescribing these drugs to persons at higher risk,because the duration of disease is shortened by a day or so. With respect to otherwise healthy flu patients,the Lancet report clearly states that the use of anti-viral drugs is ‘unlikely to be the most appropriate course of action’,while cautioning that ‘any strategy that increases the availability of the drugs to the general public,consequently increasing the rates of inappropriate use,could increase the chances of viral strains developing resistance’.

There is,of course,an understandable inclination to proactively treat children,both because of their vulnerability and because,in pandemic conditions,they represent the future not only of families and nations but also of the human species. However,even here too,evidence suggests that drug therapy should be restricted to clinically more severe cases. The majority of cases,which are mild,should be treated with other measures. Post-exposure prophylaxis,in otherwise healthy children in UK,was associated with variable adherence to treatment (48 per cent to 77 per cent) and a high incidence of unpleasant side effects (51 per cent to 58 per cent). Overcautious overuse is also fraught with a risk of drug resistance.

Indeed,it is the emergence of drug resistant H1N1 strains that needs to be watched carefully. Already,such strains have been reported in USA,Canada,US-Mexico border,Netherlands and Hong Kong. We need to be on alert for drug-resistant strains emerging in India or entering from other countries.

HEALTH SERVICES WATCH: Presently the health services are mounting a ‘containment’ response involving case isolation and contact tracing. Since the H1N1 virus is highly transmissible,it is very likely that the virus will infect more people,circulate in the communities of affected cities and travel to other parts of India. Outside of outbreaks in a confined setting (e.g. seasonal influenza outbreaks in residential homes or hostels),history shows that it is almost impossible to contain influenza. Even in a confined setting,mass strategies (like immunization or prophylaxis) are needed.

Diffusion of the virus in the population would require the health services to switch to a ‘mitigation’ response mainly focusing on ensuring healthcare for those affected,prioritising the protection of the most vulnerable. Health services across the country need to be prepared to handle these demands,following appropriate clinical and public health guidelines.

In other countries,a combination of initial containment and later mitigation strategies saw the peaking of the epidemic around 7-10 weeks after the appearance of the first cases. In a large country like India both of these strategies would need to be pursued,based on the appearance or spread in different parts of the country.

MEDIA WATCH: Since the media too displays ‘drifts’ and ‘shifts’ in its coverage of public health issues,it would be important to examine how its members respond to the changing scenarios and choose to educate or excite the public. This will be especially important in the coming months,as the H1N1 virus will certainly spread for sometime and the seasonal flu viruses arrive to keep it company.

The authors are president and senior public health specialist respectively,at the Public Health Foundation of India.