A fairly large number of people die from influenza every year, but we don't have a mass surveillance dragnet to try and isolate flu vectors, for good reason. We do, however, have a fairly robust vaccination system which is a sensible precaution to take.
But it's completely wrong to conclude that the right thing to do is therefore nothing. As we learn more about who, what, why, and how this happened the first goal is to hunt down, arrest, put on trial, and if found guilty imprison for the rest of their lives (or execute) anyone who contributed to this attack. Every angle must be criticized to understand what effective countermeasures could have been in place to detect, disrupt, or kill the attackers sooner. There should be a tremendous outpouring of support for all the people and families impacted.
The most sickening is the celebratory response from various camps, and I wonder if that's happening anywhere inside France.
Particularly if this turns out to be a home brew attack, the Islamic communities bear a tremendous responsibility, not for the attack, but going forward, in significantly strengthening and mobilizing all their resources towards preaching nonviolent protest and leading the efforts to root out radicalized groups in the community. Where are the Islamic MLKs to rally the community against radicalization? The fear-and hate-fueled backlash against French Muslims may only be stemmed by a disproportionate response against the violence from within the communities.
And just a pedantic point, we actually do spend a reasonable sum on detecting flu trends by "surveillance" of hospital visits and even monitoring Google searches to identify and better respond to possible outbreaks.