Population susceptibility to infection by a new virus drives the dynamics of an influenza pandemic. This is the critical question. Are there enough susceptible people left to sustain further waves of community-wide transmission? At present, we simply do not have enough data to answer this question with certainty. Studies are, however, under way.
We can estimate how much immunity has been conferred through vaccination. But knowing how much natural immunity has been acquired through infection is more difficult, especially given the very mild nature of illness in the vast majority of patients. Some infections produced no symptoms, and quick surveys of influenza-like illness will not capture these infections.
Although the virus has not yet delivered any devastating surprises, we have seen some surprises on other fronts. ……..But we did not anticipate that people would decide not to be vaccinated. …. People make their own decisions about what information to trust, and base their actions on those decisions.
The days when health officials could issue advice, based on the very best medical and scientific data, and expect populations to comply, may be fading. It may no longer be sufficient to say that a vaccine is safe, or testing complied with all regulatory standards, or a risk is real…… In terms of managing public perceptions, part of the problem arises from the big difference between what was expected, after watching the highly lethal H5N1 virus for so long, and what fortunately happened. An event similar to the 1918 pandemic was feared, when what actually happened is probably closer to the 1957 or 1968 pandemics.
Let me introduce a word of caution. Reliable estimates of the number of deaths and the mortality rate during the current pandemic will not be possible until one to two years after the pandemic has ended.