Isn’t taking a vaccine against a potentially serious disease the easiest of decisions to make? Indeed so, if the ailment in question is swine flu, a pandemic which spread all over the world since it was first detected in Mexico and the US in April this year. But a recent study by the University of Pittsburgh Graduate School of Public Health, the US, came up with a surprising finding: the decision to take the vaccine was in the negative. Only 10 per cent of those surveyed said they were willing to have it administered.

Swine flu vaccine is now available in the US as a spray for children, and will be available as shots for adults soon. However, many Americans have decided not to vaccinate themselves. The reasons are various — the vaccine is untested, it uses adjuvants that are toxic, it causes a rare nervous disorder, and so on. Critics cite the deaths caused by a swine flu vaccine in 1976, when the US government embarked on a mandatory mass vaccination campaign.

Several interest groups campaign against vaccinations. In New York, healthcare workers protested against mandatory swine flu shots, forcing the authorities to make the vaccine optional.

“There also remains a significant shortage of the vaccines in many countries,” says Sandra Quinn, author of the Pittsburgh study. “Given this, our finding that few people would accept a new but not yet fully approved H1N1 vaccine or drug is worrisome.”

This leaves the US public health authorities faced with a double problem — make the vaccine in large numbers, and persuade people to take it.

The swine flu situation has reopened an old debate in the US, and would possibly do so in other countries. What should one do when a potentially serious pandemic looms, particularly when we do not understand the disease or the culprit well enough? Should authorities vaccinate everybody or only a few high-risk individuals? Who is a high-risk individual for swine flu anyway when it is young healthy people who die the most? If there is little time to develop and test a vaccine, as in this case, what should an individual do? Take the vaccine and hope for the best, or not take it and hope for the best?

Scientists often encounter situations the essence of which they may not understand. For example, we still do not completely comprehend things like gravity, photosynthesis, earthquakes or viruses. We do not understand precisely how some common diseases are caused, or how many drugs work. In the absence of a clear understanding, scientists resort to one practice, particularly in medicine — use statistical analysis to formulate strategies.

In the case of swine flu, the statistics tell a clear story. The ailment is far more dangerous than seasonal flu, probably 10 times more. About one in 10,000 infections result in death, compared to one in 1,00,000 in seasonal flu. Moreover, there is a possibility that the virus would turn more virulent later in the winter. Vaccination, however, is at times risky. It causes some temporary side effects, and in some rare cases, paralysis. So which way would a person go? “In such circumstances, see what does the maximum good for the maximum number people,” says Michael Ranney, statistician and associate professor of cognition and development at the University of California in Berkeley. Ranney studies reasoning and policy making that involve socially important rates and statistics.

The arguments against the vaccine seem serious at first hearing. It uses a mercury-based compound as an adjuvant, an agent that is added to the vaccine to increase its efficacy. Fears linger from the 1976 programme in the US. Out of the 48 million people given the vaccine, 532 developed a form of paralysis called Guillain-Barré syndrome that was fatal in some cases.

However, vaccine technology as we all know has improved considerably in the last 30 years. The adjuvant would be used in some multiple shot vaccines, but as a compound of mercury that has been used in many vaccines in the past. Despite everything, the fact remains that even the seasonal flu vaccine causes paralysis in one in a million cases.

So what should one do? When you balance the risks of taking and not taking the vaccine, there is no doubt which is better. Vaccination causes paralysis in one in a million cases, while flu causes the same disease in 40 out of a million cases. Says T.S. Sridhar, neurologist and professor of molecular medicine at St Johns Hospital in Banglaore, “Guillain-Barré syndrome is rare, and 95 per cent of patients recover from it.”

“Americans do not realise that one in a hundred gets killed on the road,” says Ranney. In that sense then, taking a vaccine is one of the least risky things that we do in life.