I just got my flu shot. I know the official flu season started two months ago and that it will be, at best, three weeks before the vaccination starts to protect me, if it actually works. Recently, there has been increasing skepticism regarding benefits of this vaccine. I am a scientist who has worked with infectious diseases for more than 30 years, and being skeptical was a big part of the job. Having considered all the arguments for and against the vaccine, I made an informed decision and rolled up my sleeve.

First let’s consider the cons, the reasons why you might hesitate being vaccinated.

To begin with, creditable scientists have offered conflicting judgments in both the popular and scholarly press about the shot’s effectiveness. Some claim it is generally beneficial, others say it is helpful, depending on factors such as age and health. Still others maintain that it is completely worthless. Our present vaccines are clearly not universally protective, but neither were others that have all but wiped out diseases, such as polio, mumps and chickenpox.

Another problem with the vaccine is that it is offered without prior testing.

Every year, scientists try to predict what type of flu will strike us next by determining which virus is dominant in other parts of the world where outbreaks are occuring first. By the time they are able to make their determination there is not enough time to first test and then produce the vaccine before flu season begins here.

Because the shots cannot be tested, it is possible that they will have side effects that are nastier than the flu itself. Flu shots have been implicated in the onset of both autism in children and Alzheimer’s disease in adults, although neither of these claims has much support.

It is important to remember that every vaccine ever formulated has carried risk, including those that successfully pushed back deadly diseases like polio. And yet, who today can regret that nearly everyone took their chances, whether they knew it or not, and got those shots?

Now for the pros.

Although vaccines are not totally protective for each individual inoculated, they can act like a firewall to prevent the spread of disease within a community. The flu is highly contagious. Each infection can, on average, result in two new infections. Each new infection can in turn causes two more, for a total of four and then eight in the two next cycles.

If, on the other hand, the rate of spread dropped from two to less than one for each infection, the disease would soon die out. It is therefore critical to reduce the rate of spread by any means possible and vaccine, even if it is only partially protective, is the best means we have.

For the sake of argument, let us say that this year’s flu vaccine will be 50 percent effective. If everyone receives this vaccine, the rate of spread will be cut at every cycle of infection and the disease may either not become established in a community or rapidly disappear.

That is why you should get your flu shot. It’s all about herd immunity, that it is selfish not to protect yourself from infection because if you succumb to it you are likely to make other people, possibly a lot of other people, sick. For anyone between six months and 65 years of age and in good health, the effect of the flu is generally limited to a relatively short period of acute discomfort, but for those under six months or over 65 years, as well as anyone with underlying health problems, there is an elevated chance of serious complications.

Because the disease is so contagious, and because one can easily transmit the disease prior to feeling any symptoms, unvaccinated individuals who have nothing worse to fear from the flu than a week or so of misery are likely to spread it to more vulnerable members of their families or communities before they even realize they are carrying it. It is possible, depending on chance and the length of the flu season, that one could, without ever knowing it, cause 32 or 64 people to become ill. The likelihood of one of them suffering severe, perhaps fatal, complications is just too high to justify not getting the vaccine.

In truth, we still don’t have a handle on this disease. The U.S. Centers for Disease Control and Prevention reports a range of flu deaths from 3,300 to 40,000 each year. We are even less clear, if that is possible, about how many people contract the flu each year. One reason for this uncertainty is the fact that hundreds of pathogens can cause symptoms similar to flu. Respiratory syncytial virus, bocavirus, coronavirus, and rhinovirus are just a few of the bugs that can make a person feel equally rotten. Only recently have procedures to diagnose the major types of flu virus become available in hospitals. This is a blessing for surveillance of the disease because it serves to spot outbreaks much more rapidly and accurately.

Unfortunately, we do not yet have the means to track the course of infection from one person to the next, or to associate either rapid transmission or extreme virulence with a particular subtype of the flu. When these techniques become widely available our success in epidemiological intervention will be greatly increased.