Q: I read a newspaper article that says the World Health Organization (WHO) has announced that the H1N1 pandemic is over. Does this mean we have somehow eliminated this virus already?
--Georgia N., Davao City

A: The August 10 announcement by WHO Director General Margaret Chan that the H1N1 pandemic is over does not mean that the H1N1 strain of the influenza virus has been eliminated. In fact, the strain is still very much around and will continue to circulate worldwide but with a new role—as one of the numerous strains of the flu virus that can cause seasonal influenza.

There are three types (A, B and C) of the influenza virus that can cause flu. Each has several subtypes or strains. H1N1 is a strain of the type A virus.

Every year, localized outbreaks of flu occur in practically all countries during particular seasons. The seasonal influenza outbreaks in any given year are usually caused by only one strain of the virus, but because the numerous strains of the flu virus undergo frequent mutation, the strain that causes outbreaks changes from year to year.

Occasionally, one strain of the flu virus mutates in such a way that it is able to spread rapidly all over the world. When this happens the strain causes a pandemic; and this is what H1N1 has done the last year.

Flu pandemics occur three to four times each century. In the last century, they occurred in 1918-19, 1957-58 and 1968-69. The strain that caused the 1918 pandemic, which is also known as the Spanish flu pandemic, was a particularly virulent one. It killed between 20 to 100 million people.

The current H1N1 strain of the flu virus first surfaced in Mexico in April of last year. It spread so fast that the WHO already declared a pandemic just two months later. Declaration of a pandemic depends on the geographic spread of the circulating influenza strain, not its severity. As it turned out, the H1N1 virus is not as virulent as was initially feared. The resulting morbidity and mortality figures from the pandemic it caused are not very high. To date, confirmed deaths worldwide from H1N1 flu total 18,450 — a figure that is much lower than that caused by the other seasonal influenza viruses, which is estimated to be at 500,000 per annum. In the Philippines, the fatality rate of H1N1 is even much lower, only 30 deaths have been reported before we stopped counting, and many of those who died have other existing medical conditions.

Presently, the H1N1 virus has evidently run its course as a pandemic and from now on (as I mentioned at the start of this article) it will simply be one of the numerous strains of the influenza virus that can potentially give rise to seasonal outbreaks.

The best way to prevent flu is by active immunization or vaccination against the disease. However, the vaccine has limitations. It is only 65 to 80 percent and 30 to 40 percent effective in young adults and the elderly, respectively. Furthermore, it confers protection for a maximum of 12 months only. Hence, it has to be administered every year. Also, the composition of the vaccine has to be changed annually because the prevalent strains of the virus vary from year to year and also because it is not technically possible to incorporate all the strains of the virus in one vaccine.

This year, the US Center for Disease Control has recommended that all persons above six months of age be immunized with the flu vaccine. Incidentally, the flu vaccine this year has been designed to confer protection not only against the old strains of the virus but also against H1N1.

(E-mail inquiries on health matters to: medical_notes@yahoo.com or wellbeing@mb.com.ph)