The National Infectious Disease Forecast Center has received several inquiries regarding H1N1 influenza activity in the US this season. Here we would like to share our observations:
- The National Infectious Disease Forecast Center publicly forecasted anticipation of an A/H1N1-dominant season with excellent vaccine match beginning in August. Expectation was that it would be a mild season.
- Thus far, physicians and infection control practitioners directly involved with patient care of H1N1 cases in Mexico, the US, and Canada have unanimously indicated ICU admissions and fatalities are seen in unvaccinated patients. In a minority of cases, they are unclear about vaccination history.
- All H1N1 isolates submitted to CDC have matched this season's vaccine strain based on reporting from Week 52. At a national level, the overall picture of the season is mild/moderate. There is a slight inflexion of the epi curve reported in Week 52. We are hopeful this is indicative of peaking out, however prior seasons have shown a similar brief inflexion before additional case surge. Obviously, monitoring subsequent reports will shed more light on where we are going with this.
- It is our belief that, from the perspective of those individuals who have chosen not to vaccinate for this year's influenza, we are basically seeing another pandemic wave of H1N1 transmission with the associated potential for severe clinical outcomes. For those who are vaccinated, the experience is a mild one.
Point #4 highlights a bit of irony for our team, where we are attempting to forecast certain features of the influenza season. What we have found is the possibility of anti-vaccination politics playing a major role in interfering with the validation of our forecast. We have observed through direct clinical experience that anti-vaccination sentiment, particularly for influenza, remains strong in the US and are tied to politics. It is clear to those of us monitoring the situation that such views have a mortality rate.