To boost or not to boost. That is the question for health officials studying whether adults need a booster shot for tetanus and diphtheria after they’ve received their childhood vaccinations for the infections.

In the United States, the recommendation by health officials is that adults get a booster for both infections every 10 years. But the World Health Organization does not recommend one. In fact, 10 European countries do not require them.

But recent research might tip the balance. An epidemiological study published in the journal Clinical Infectious Diseases found no difference in the rate of infection between countries that require a booster and those that don’t. Scientists reached that conclusion after examining the equivalent of 11 billion-person years of incidence data.

Previous immunological investigations had suggested booster shots were unnecessary. They found childhood vaccinations for tetanus and diphtheria offered long-lasting protection.

The bacterial infections were once greatly feared but have been nearly eradicated in industrialized nations like the United States. Tetanus, also called lockjaw, at one time had a mortality rate of 91%. Diphtheria, an infection of the throat and upper airways, was fatal in up to 10% of cases.

Some physicians urge caution when viewing the study’s conclusions. They note there are documented cases of tetanus, for example, long after vaccination, indicating a booster shot could be helpful.

One thing is clear: There would be a considerable impact on the U.S. health care industry if the booster shots were eliminated — up to $1 billion annually.