Today I received an email from a reader whose family is planning a visit to several places in Colombia. The reader wanted my opinion on the risks of contracting Zika (and especially Guillain-Barré syndrome) in those destinations.
Such questions make me anxious. They are far above my pay grade as a retired English teacher and author of SF novels. But I dug out the link to the latest Epidemiological Bulletin from Colombia's National Institute of Health and pointed out some graphs and a map. My interpretation was that Zika and GBS are in decline (no GBS cases were reported at all in the current week 20 report). I also noted that despite all the Zika cases since last fall, only five Zika-related microcephaly cases have been confirmed.
Coming from me, this advice was free and worth every centavo my reader paid for it. But as I was re-reading the bulletin numbers, something occurred to me, and I'd appreciate the advice of people who know a lot more than I do.
Colombia has reported about 87,000 confirmed and suspected Zika cases since last fall. Zika is a disease that appears to be asymptomatic in 80% of those who contract it. (Presumably they can still pass it on to mosquitos or sexual partners, but please correct me on that also.) In that case, the total number of Colombian Zika cases is around 435,000. If symptomatic cases have been under-reported, then the total is even higher.
So is it possible that Colombians could already be acquiring some herd immunity, even if their total population is some 48 million? And could that herd immunity also protect travellers from outside the country?
I haven't seen the Brazilians make such a claim, though it would be in their interest to do so. And just a handful of Colombian departments, especially Norte de Santander, seem to take a beating from Zika week after week. So maybe this herd-immunity idea is at best premature. But I would be grateful for advice from the grownups on this.