Q: Why didn’t viruses like polio mutate to become immune to vaccines?

A: “Bacteria mutate very well, but vaccines don’t give viruses much of a chance,” said Dr. Paul A. Offit, chief of infectious diseases at the Children’s Hospital of Philadelphia.

The way it works with the measles vaccine, for example, is that a live, weakened form of the virus is given, so that the body develops antibodies directed against all 10 of the virus’ proteins and all the sites where it might attach to the body’s cells. “When the virus tries to infect you, it really doesn’t have a chance,” Offit said. “You attack it at all possible points.”

Polio has three serotypes, or types of surface proteins, but they were all in the vaccine. Mumps, German measles and chickenpox all have single serotypes.

It is different with bacteria, he said, because there are already resistant bacterial strains out there, so vaccination provides a fertile ground by eliminating sensitive strains, allowing resistant strains to thrive.

“With a virus, this never gets started,” Offit said. “I suppose if you were making a vaccine against one part of one protein, it might allow mutation, but we don’t give it a chance.”

There are two important exceptions, he said: influenza, which mutates so quickly that immunization one year does not protect from the next year’s strains, and HIV, which can mutate during a single infection.

Study: Fans may slow down body’s cooling

Q. Can an electric fan cool you off in a heat wave?

A. The heat waves that have scorched parts of North America this summer may become all too familiar — climate scientists say they are likely to occur with increasing frequency.

When air-conditioning is not an option for relief, an electric fan may seem like the best alternative. But some experts have questioned whether electric fans might actually hamper efforts to cool down.

In a new study, a team of researchers based primarily in Britain sought to review evidence on the effectiveness of electric fans during heat waves that have occurred all over the world.

Despite what many people think, most fans do not directly cool the ambient air. When placed in an open window, they pull in cooler air from outside. But there is a point at which their effectiveness may diminish.

The authors of the new report pointed out that when temperatures climb past 35 C, having a fan pointed at you can actually contribute to heat gain, not reduce it.

At those temperatures, being directly in the path of hot air blown from a fan can raise the risk of dehydration and heat exhaustion.

The researchers said that while they could not support or recommend against the use of electric fans in sweltering conditions, it was important to consider their potential harms and benefits.

That is especially the case for vulnerable populations like the elderly, “who are less able to cool down through sweating or increasing the flow of blood to their skin,” the authors wrote.

The New York Times