Exactly two years after the Fukushima nuclear disaster, perhaps the most crucial issue to be addressed is how many people were harmed by radioactive emissions.

The full tally won’t be known for years, after many scientific studies. But some have rushed to judgment, proclaiming exposures were so small that there will be virtually no harm from Fukushima fallout.

This knee-jerk reaction after a meltdown is nothing new. Nearly 12 years after the Three Mile Island accident in 1979, there were no journal articles examining changes in local cancer rates. But 31 articles in publications like the Journal of Trauma and Stress and Psychosomatic Medicine had already explored psychological consequences.

Eventually, the first articles on cancer cases showed that in the five years after the accident, there was a whopping 64% increase in the cancer cases within 10 miles of Three Mile Island. But the writers, from Columbia University, concluded radiation could not account for this rise, suggesting stress be considered instead. While this was later contested by researchers from the University of North Carolina, many officials still subscribe to the slogan “nobody died at Three Mile Island.”

In 1986, after the Chernobyl catastrophe, officials in the Soviet Union and elsewhere raced to play damage control. The Soviet government admitted 31 rescue workers had died soon after absorbing huge radiation doses extinguishing the fire and trying to bury the red-hot reactor. For years, 31 was often cited as the “total” deaths from Chernobyl. Journal articles on disease and death rates near Chernobyl were slow and limited. The first articles were on rising numbers of local children with thyroid cancer – a very rare condition.

Finally, 20 years after the meltdown, a conference of the World Health Organization, International Atomic Energy Agency, and other groups admitted to 9,000 cancers worldwide from Chernobyl. But this was a tiny fraction of what others were finding. A 2009 New York Academy of Sciences book estimated 985,000 deaths (and rising) worldwide fromChernobyl fallout. The team, led by Alexey Yablokov, examined 5,000 articles and reports, most in Slavic language never before available to researchers.

Fukushima was next. While estimates of releases remain variable and inexact, nobody disputes that Fukushima was the worst or second-worst meltdown in history. But predictably, nuclear proponents raced to assure the public that little or no harm would ensue.

First to cover up and minimize damage was the Japanese government and nuclear industry. John Boice of Vanderbilt University went a step further, declaring “there is no opportunity to conduct epidemiologic studies that have any chance of detecting excess cancer risk. The doses are just too low.” At a public hearing in Alabama in December, U.S. Nuclear Regulatory Commission official Victor McCree stated “there was no significant exposure to radiation from the accident at Fukushima Daiichi.” Just days ago, a World Health Organization report concluded there would be no measurable increase in cancer rates from Fukushima – other than a very slight rise in exposed children living closest to the site.

Others have made estimates of the eventual toll from Fukushima. Welsh physicist Christopher Busby projects 417,000 additional cancers just within 125 miles of the plant. American engineer Arnold Gundersen calculates that the meltdown will cause 1 million cancer deaths.

Internist-toxicologist Janette Sherman and I are determined to make public any data on changes in health, as quickly as possible. In the December 2011 International Journal of Health Services, we documented a “bump” in U.S. deaths in the 3-4 months after Fukushima, especially among infants – the same “bump” after Chernobyl. Our recent study in theOpen Journal of Pediatrics showed rising numbers of infants born with an under-active thyroid gland – which is highly sensitive to radiation – on the West Coast, where Fukushima fallout was greatest.

It is crucial that researchers don’t wait years before analyzing and presenting data, even though the amount of available information is still modest. To remain silent while allowing the “no harm” mantra to spread would repeat the experiences after Three Mile Island and Chernobyl, and allow perpetration of the myth that meltdowns are harmless. Researchers must be vigilant in pursuing an understanding of what Fukushima did to people – so that all-too-common meltdown will be a thing of the past.

Joseph J. Mangano MPH MBA is Executive Director of the Radiation and Public Health Project.