SOME GOOD NEWS ON SMALLPOX
Joshua Epstein of Brookings and Donald Burke of Hopkins report the results of an agent-based simulation showing that pre-vaccinating all hospital workers and 60% of the general population, and then vaccinating all family members of confirmed cases while the outbreak is going on has a very good chance of “quenching” an outbreak. The good news is that about 60% of the population has been vaccinated in the past. That probably doesn’t give them immunity, but Epstein and Burke report that the side effect risk is an order of magnitude smaller for those previously exposed. They’re being careful in what they say, but it sounds like a plan to me.
One caveat: their model assumes a single “index case” in a town, or rather a pair of towns, with a total population of 800. They point out that, one case in 800 is equivalent to 15,000 infected in Manhattan. But they’re assuming that the “attacker” is a single person who has infected himself, rather than a small crew armed with nebulizers spraying virus into the air at airports and in subway stations. Since, as they point out, by the time someone’s smallpox has reached the infectious stage that person is usually too weak to walk, it seems to me that the nebulizer attack is the more plausible threat. I’d want to see how robust the model is to that change in assumptions.
But the fact about the low side-effect risk for the previously vaccinated is tremendous news. Not having to think about vaccinating kids means a much lower level of emotion surrounding both the policy discussion and the implementation. Assuming that 60% would really do the job, the big remaining question is how great the risk would be to the immunocompromised population if people around them were being vaccinated. Some of the chatter has suggested that the infection risk comes entirely or almost entirely from either touching the vaccination site directly or being touched by a vaccinee who has himself touched the site. If that’s right, the risk should be manageable, especially since we’re going to be dealing with adults. If the direct mortality risk from re-vaccination is on the order of 0.1 to 0.3 per million, then 160 million re-vaccinations would produce something under fifty deaths, or about a third of the daily highway death toll.
This rates an enthusiastic, if still tentative, “Whooppeeeeee!”