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An update on the novel influenza A virus
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We now can look back upon the events of the past month with greater insight into what has happened and try to look ahead to what is to come.
The main concerns have been how virulent is this virus and how contagious is it? In retrospect, the first reports out of Mexico may have been very misleading in terms of virulence. As the epidemic is now global in nature, it is apparent that it spreads readily and is not as serious as the initial reports suggested. A greater elucidation of the molecular virology may help us understand how this epidemic started and perhaps, more important, what does the future bring. Here, the major question is what will happen next influenza season and how we will prepare for it.
The present WHO Director-General, Margaret Chan, was intimately involved in containing the SARS outbreak, which very possibly influenced her reaction to the initial reports from Mexico. The deaths in the United States are few, most associated with underlying conditions.
Although the spread appears to be less than initially suggested from the Mexican experience, it is suspected that there are more infections than have been reported as many may have been too mild to be brought to medical attention. There have been enough school outbreaks to confirm that this virus passes readily from person to person. In some instances, schools have been closed but there is little evidence that this will be very effective. It is clear that people are contagious prior to the onset of symptoms. Keeping children home affects families and absents them at a time of year when they are preparing for final exams.
Our recent experience with avian flu has taught us that this agent is very virulent but does not seem to spread readily amongst humans.
Why did the novel flu jump?
We get some clues from the molecular virology. Apparently, influenza from swine have infected humans sporadically during the past decade but is different from the current novel strain in that it generally affected persons in contact with swine and did not spread readily in humans (www.nejm.org 2009; 10.1056/NEJMoa0903812). The novel swine strain is from a different lineage and does spread from human to human.
It is anticipated that once the summer comes, this epidemic will end as is usual with influenza epidemics. General recommendations to prevent spread can be found on the CDC’s website (www.cdc.gov/flu/professionals/infectioncontrol/maskguidance.htm) and include discouraging those who have fever and/or respiratory signs from going to public places and practicing good hygiene.
Other suggestions:
- Cover noses and mouths when coughing or sneezing,
- Use tissues to contain respiratory secretions and, after use, dispose of them in the nearest waste receptacle, and
- Perform hand hygiene after having contact with respiratory secretions and contaminated objects/materials.
What does this portend for the next influenza season? The current strain has infected those in the southern hemisphere where their winter and the influenza season is soon to start. The unknown is whether this readily transmissible strain passing from one person to the next will become more virulent. This appears to be what happened in the 1918-1919 epidemic. If this occurs, we may be in for a very bad flu season next year.
The other fear is that it may develop resistance to the neuraminadase inhibitors, which we have seen with seasonal flu. In the U.S., the recommendations for use of these drugs has been more restricted of late to try to prevent this from happening.
Oseltamivir given within 48 hours of the onset of symptoms is recommended for children younger than 5 and particularly younger than 2, pregnant women and those at high risk of complications from influenza. The FDA has during this emergency permitted the use of oseltamivir in those less than 1 year. The recommended dosages appear in the table (http://www.cdc.gov/h1n1flu/recommendations.htm). The use is discussed in Dr. Bell’s column in this issue (See this issue's Pharmacology Consult story).
The other question concerns a new vaccine for this novel strain. Whether there will be enough eggs from suitable chickens to make both vaccines against seasonal and the novel influenza viruses is problematic. The new vaccine would have to be manufactured and tested very quickly, which at a minimum would probably be half a year. If there were not enough vaccine for everyone, as there likely will not be, who would get it? Will it be possible to combine the seasonal flu with the novel flu vaccines? A few questions to ponder.