Waves of influenza

Research on previous pandemics shows that they tend to come in waves. All of the previous well-known influenza pandemics (1889, 1918, 1957, 1968) started off with an initial, mild wave of illnesses. After that peak of activity, the virus seemed to die down, only to return in a more devastating wave or waves a few months to a year later.

Margaret Chan, head of the World Health Organization (WHO), told the UN General Assembly that while there’s no indication right now that current outbreak of the new H1N1 flu is similar to the 1918 pandemic, the virus may return, stronger, later on. A second wave of disease could be more lethal. So monitoring is critical.

(The high humidity of summer and increased exposure to ultraviolet light typically brings the flu season to an end. So we might well see the epidemic of 2009 H1N1 flu end for a few months in the northern hemisphere. But flu season is only beginning in the southern hemisphere, and virologists will be watching.)