Controls are needed

16 May 2009, The Straits Times

Question

Name of the Person: Professor Lee Wei Ling

Let it in while benign to develop herd immunity

THE Influenza A (H1N1) virus is rapidly sweeping over the United States, Europe and Asia. It will be impossible to prevent the virus from entering Singapore just by screening those entering here who are ill and/or febrile.

We know that of all the patients who carry H1N1, at least 30 per cent are asymptomatic, and even those who will become symptomatic are infectious for at least the first 24 hours before symptoms appear. However, we are still doing temperature screenings at our borders and other public sites and buildings. A false negative is highly likely and is worse than not screening at all as infectious individuals may then go around thinking that they are well.

World Health Organisation director- general Margaret Chan warns that the virus may well return in a more virulent form after lying dormant in the warm months of the northern hemisphere. Singapore needs to rethink its strategy in this respect while we still have time.

We should stop temperature screening, which is ineffective for picking up infected subjects. When the pandemic started, there was a concern that it could be a virulent disease which makes sense for countries to err on the side of over-cautiousness and adopt stringent measures to prevent its spread. The situation has since changed as we learn more about the H1N1 virus. ?It appears to be highly contagious, but with low morbidity and mortality. ?

One possibility suggested by some doctors, including specialists in infectious diseases, is to freely open our borders, allow the relatively benign H1N1 to come into Singapore and allow our people to develop herd immunity. This way, if or when the virus mutates and turns virulent, our herd immunity may better protect us from a serious epidemic. In my view, there is merit in this idea. Continuing with the present strategy may invite more risks.

Reply

Name of the Person: Dr Lyn James

Director, Communicable Diseases Division

Ministry of Health 

In "Let it in while benign to develop herd immunity" (ST, 13 May) Dr Lee Wei Ling has questioned the basis for temperature screening at border checkpoints as about one third of the people infected with the influenza virus are asymptomatic, and even those who will become ill are infectious for at least 24 hours before symptoms develop.

The Ministry of Health has taken into consideration these clinical and epidemiological features in implementing border control measures. Infection is spread largely by coughing, sneezing or a runny nose; through those who are already symptomatic. The spread of infection by an asymptomatic infected person is unlikely to be of significant public health importance.

In the containment phase when there is no community transmission, border temperature screening, isolation of cases and contact tracing are the main strategies. Febrile travellers detected will be sent by dedicated ambulance to the Communicable Disease Centre for further investigation. Incoming travellers are issued health advisory on what they should do should they become ill following travel to affected countries. It would be premature to abandon border control at this stage when we don't even have a case. We will continue with this measure to delay the onset of sustained community transmission.

With community spread, the key to prevention and control is for everyone to be socially responsible by practising good personal hygiene and social distancing. These measures take on greater significance when we are ill.

The novel H1N1 virus is still evolving and currently, its rate of spread and mortality are higher than those of seasonal flu. It should not be taken lightly. Persons infected with this strain as well as their contacts might develop severe complications or die. One cannot predict the risks to himself or his contacts to whom he may inadvertently spread the disease. We need to protect the vulnerable groups such as the very young, the very old and those with underlying chronic conditions.