Journalists’ questions on swine flu answered

The Science Media Centre in London compiled answers to questions on swine flu posed by UK-based journalists – answers courtesy of Dr John McConnell, Editor of The Lancet Infectious Diseases.

1: Can you comment on early detection methods and vaccine synthesis?

[John McConnell] Detection methods not really my thing. I understand that the US CDC has produced a seed stock of the virus from which a vaccine could be produced. Vaccine manufacture could take 3-6 months and worldwide there is sufficient capacity to produce about 400 million courses of flu vaccine per year.

2: Is screening at airports a waste of time?

[John McConnell] Probably, although it might slow the spread of disease. During the SARS outbreak in 2003 millions of airline passengers were screened at international airports by heat-sensitive cameras and similar devices, and precisely zero cases of SARS were detected.

3: Why does the flu seem to be less deadly outside of New Mexico, is it the disease changing or simply better healthcare in more developed countries.

[John McConnell] Hard to give a firm answer. The virus seems to be the same in Mexico, USA, and Canada. Probably better access to healthcare in USA and Canada is a factor. However, so far only 18 of the about 1600 suspected cases in Mexico have been confirmed virologically, so not possible yet to be definitive about the incidence and mortality rate of the disease.

4: What do we know about the disease? What don’t we know?

5: How quickly might it spread?

[John McConnell] The incubation period (time between infection and symptom onset) of influenza A is under 2 days, with a range of 1-4 days. The Mexican swine flu virus seems to have been around at least since mid March, which means it might have had the opportunity to spread globally already. Together, these factors suggest that if swine flu is going to spread worldwide, we will likely see local outbreaks within the next 1-2 weeks.

I see a case has just been confirmed in Spain.

6: How bad is it going to get?

[John McConnell] Insufficient data to answer this question yet. Estimates of 50-120 million dead, as I’ve seen in the press, are pure speculation.

7: The basic virology of flu — how do new viruses like the Mexico strain arise? What makes them nasty?

[John McConnell] By mutation and mixing of elements of the virus genome that might originate from people, pigs, or birds.

8: Why do the US and Mexico flanks of the outbreak apparently look so different?

[John McConnell] See above, but basically we don’t know.

9: Will there be any cross-immunity between normal H1N1 and the Mexico strain?

[John McConnell] Variants of the H1N1 form of the influenza A virus have been circulating in the human population for many years. Indeed, the current seasonal flu vaccine is designed to protect against H1N1. So there may well be some immunity to H1N1 at the population level that will provide a degree of protection.

10: What plausible explanations are there for the apparent mismatch between what’s mexico and the united states.

11: What are the chances of this year’s seasonal flu vaccine containing anything that might offer protection against this strain?

[John McConnell] See 9 above.

12:  A reminder of a timeline for flu transmission including when symptoms develop, when people are infectious and not etc.

[John McConnell] Incubation period 1-4 days (see 5 above). Most people will recover within 1-2 weeks. People may excrete virus for around 10 days.

13:  Masks – how useful are they in offering any protection or are they simply a measure that makes people feel better?

[John McConnell] Controversial question. Probably more useful for people with symptoms to prevent them spreading infection and masks need to be changed daily to be effective.

14:  What thoughts on international travel – should any further measures be taken to screen people?

[John McConnell] See 2 above. Mathematical modelling shows that closing borders would have to be 99.9% effective to make a difference, and even then would only slow the spread of an epidemic rather than limit its magnitude. So, in effect, a pointless intervention.

15:  What are the chances of this strain mutating into a strain that is more dangerous and more virulent?

[John McConnell] Impossible to say-the influenza virus is unpredictable

16:  Estimates of timeline to develop a vaccine – should that be needed?

[John McConnell] See 1 above.

17.   An explanation of how antivirals work.

[John McConnell] Oseltamivir (Tamiflu) and zanamivir (Relenza), which have some treatment effect against swine flu, are drugs called neuraminidase inhibitors. These drugs work by blocking the function of viral neuraminidase (the “N” element of H1N1) thus preventing the virus from budding from host cells (ie, preventing it reproducing).

18: Has the focus on H5N1 in recent years led to the risks from an H1N1 strain being underestimated?

[John McConnell] H1N1 has not been perceived as a particular pandemic threat because it has been circulating among human beings. However, the focus on H5N1 has greatly increased our level of preparedness for the next flu pandemic.

19: How prepared are we and what would happen if it does come here – face masks etc

[John McConnell] The UK is as well–if not better–prepared as any country in the world. For details, best refer to the government’s published pandemic preparedness plan.

20: Are we all going to die?

[John McConnell] No.