Monday, January 14, 2013

In the Midst of an Outbreak: Better to Immunize or Not?

The flu season is well and fully upon us. In the U.S., the season generally begins in October and runs through May, with a peak sometime in February. There are a number of factors that may play a role in this cyclic nature of influenza, ranging from people being indoors more in the winter, thereby creating greater opportunity for the virus to spread, to less UV radiation that would otherwise kill the virus. Whatever the reason, the cycle is rather predictable.

This season, the flu has hit hard and early:

Source: CDC Influenza Weekly Report, January 14, 2013
The red line is the current season. Unlike most seasons, we're taking a track similar to the 2003-2004 season, with an early peak. This has led a number of regions to declare a public health emergency, meaning that states can release more resources to fight the spread of disease, such as allowing expansion of immunization clinics.

With increased rates, is this sort of declaration helpful? With influenza already in full swing, will expanding immunization help, or is it a bit of a double-edged sword?

Almost a week ago, on January 9, Boston declared a public health emergency, with widespread transmission (700 lab-confirmed cases already in the city, compared to last season's total of 70) and 18 deaths. New York state followed suit on Saturday, after receiving 19,128 reported cases, compared to the 2011-2012 total of 4,404 confirmed cases. Other areas have also considered declaring emergencies with the aim to provide greater access to influenza immunization clinics.

Given how many cases are already circulating and spreading the virus, there is a legitimate question as to whether vaccination at this point in the game will be good or bad. In particular, what impact might it have for future immunization efforts?

There's no doubt that, if you only took one step to protect yourself and those around you, the vaccine is arguably the single best thing you can do. Hand hygiene, covering coughs and sneezes and so on are all things you should be doing, but there is a far greater chance of failure in these measures than the vaccine. Diet and nutrition may have some impact on the severity if you get sick, but won't do anything to prevent getting infected or spreading the disease. A very strong argument, then, can be made for people to go out and get immunized against this year's seasonal influenza. If they have not been exposed yet, widespread vaccination can help slow the spread.

On the flip side, for those who have not already been immunized, the chances of being exposed shortly before or after vaccination are pretty high. What does that matter? you might ask. It takes a little time for symptoms to appear after infection. And as for the vaccine itself, after getting it, it takes a person about two weeks to develop enough immunity to ward off infection. What this means is that someone who is infected just before vaccination or within that two-week window following immunization might still get the flu. This is part of the reason for the common myth that the vaccine causes influenza in some people. It doesn't, but the timing makes it seem so. This is bad for public health efforts, because when it happens to someone, unless they know how the flu and the vaccine work, they will be more likely to blame the vaccine or declare it doesn't work. In future seasons, they will be less likely, then, to get immunized.

With that in mind, what are public health departments to do? On the one hand, immunizing as many people as possible as quickly as possible can go a long way toward cutting this season's outbreaks short. On the other, there is a not insignificant risk that while we might greatly benefit this year, future outbreaks will be hampered due to people's erroneous perceptions of cause-and-effect.

It is a difficult question to answer. Personally, I think the best approach is to offer the vaccine, but education is absolutely vital. The Vaccine Information Sheet that providers are supposed to give patients along with the shot mention the 2-week latency for protection, but this isn't really emphasized. Given the current state of influenza outbreaks around the country, and with public health agencies pushing for expanded immunization clinics, that point cannot be stressed enough. If patient education is lacking, then health departments will be cutting themselves as they cut the epidemic.


  1. You are right about education. I don't think enough people know about the two-week window. There's also the window before the vaccination, where you might have already been exposed but don't have symptoms yet.

    A similar situation with timing occurs when people are prescribed an antibiotic for an infection. People expect instant results and in many cases get them, but when the infection appears to go away, they stop taking the antibiotic and it comes back. (I had a tooth with a fractured, infected root. It only took a few hours for the antibiotics to knock down the infection and remove most of the pain, but I had to continue to take the antibiotic for 10-15 days for this reason.)

    When you get a vaccine or short-term prescription, the doctor, nurse or pharmacist always asks if you have any questions, but I think it would be much better if they proactively told you about this issue. For flu vaccines, they should emphasize that you aren't out of the woods yet, and for the next two weeks you still have to be careful about hand washing, coughing and sneezing, and so on, especially around people who might be contagious and vulnerable people you might unwittingly expose, such as infants and the immune-compromised. It's a lot to remember, but they have a captive audience when they give you the shot!

    BTW, on the good news front, it looks like the peak has already passed for this year's cycle. Of course the data must still be preliminary, but all the previous severe or moderately severe years show only a single peak. (The mild year (last year) and moderate year (2002-3) do show multiple peaks but they look like statistical noise.)

    I suppose that means there's some chance people getting vaccinated now (who wouldn't have gotten the flu anyway) will be convinced that the vaccines do work and will get vaccinated earlier in the future. (Confirmation bias works both ways!) On the other hand, maybe the nice symmetrical shape of previous year's curves is due to steep rise as the disease spreads followed by a steep decline as people get vaccinated, and if there was no vaccine or it had limited availability, there would be a steep rise, but a slow, erratic tapering off as milder cases (often unreported?) established herd immunity.


    P.S. If this double-posts, please feel free to delete one copy. When I clicked "Publish", the screen flashed and now it says "There was an error in this gadget" on the right between the "Blog Archive" and the "Blog Roll".

  2. Thanks for the comment, John. Only one copy of your comment came through. Looks like the "Recent Comments" widget is broken.

    As to the peak, the data are preliminary, so it can always change as the epidemiologists and lab techs sift through the reports and samples. Hopefully you're right, that we've peaked and are on the way down.

    If we are on the way down, there could be a couple things at work: a) more people have gotten vaccinated and are thus immune, leading to the decrease in spread; or b) enough people have been infected and are thus immune, leading to the decrease in spread. People may also be taking more precautions with regard to hand hygiene and staying home, but that's probably a minor factor, if it's playing a role at all.


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