A generation ago, doctors began routinely vaccinating every child against measles. No one worried much about what would happen when the children grew up and had babies of their own.

In hindsight, perhaps they should have. These new mothers fail to pass on the strong resistance to measles at birth that an eternity of women before them have done.

The result is a new problem: measles in the very young.

This unforeseen byproduct of a well-meaning public health campaign has become apparent over the last two or three years, as larger numbers of vaccinated women have reached their childbearing years. Because the mothers got vaccinated, their babies are unusually susceptible to measles in their first year of life, when it is a potentially life-threatening disease.


Now, more than one-quarter of all U.S. measles victims are under a year old, an age when this disease was once almost unheard of.

“It’s an extremely interesting phenomenon, and one of great concern,” said Dr. William Atkinson of the U.S. Centers for Disease Control and Prevention in Atlanta.

Experts caution that this does not mean that girls should not be vaccinated. In fact, the disease is overwhelmingly less common than it was until the 1960s, when virtually everyone caught it. They contend that measles would not be a problem now for newborns, either, if the vaccine were more widely administered to preschool toddlers.

Nature once took care of this matter nicely. Before the vaccine era, when measles was an unavoidable rite of childhood, everyone who recovered carried high levels of measles antibodies for the rest of their life. This kept the virus from coming back.


When women give birth, they pass on this protection to help babies ward off measles until their own immune systems mature. Infants begin life with their mothers’ measles antibodies already circulating in their bloodstreams.

The amount of antibodies a baby gets at birth depends on how much the mother carries. If the mother has a lot, so will the child.

Like a natural measles infection, the vaccine triggers production of measles antibodies. However, the amounts are lower. So vaccinated mothers have fewer antibodies to pass to their babies than do those who actually caught the measles and suffered through the disease.

This means that their babies become prone to catching measles at an earlier age. The children of naturally infected mothers are often protected from measles until 15 months or so. But vaccinated mothers’ babies may be at risk at 6 months or younger.


CDC figures show how this has changed the face of measles. In 1976, just 3% of all cases occurred in children under age 1. Typically their mothers were born in the 1950s, well before the measles vaccine became routinely available a decade later.

In the 1980s, as teen-agers who were vaccinated as children began to have babies, those numbers started to change. In 1985, almost 8% of measles cases were in infants younger than 1. By 1991, it had climbed to 19%. And so far this year, 28% of all measles cases have occurred in babies under a year old.

Measles is especially hazardous in infants because of the risk of complications. Between a quarter and a third develop some related problem, such as diarrhea, ear infections, pneumonia or encephalitis.

“It is a problem. But if we did everything else right, it would not be a problem,” said Dr. James Cherry of UCLA.


If the highly contagious measles virus were not circulating, it would not matter if babies were susceptible a few months sooner. But the virus is not quite under control. Cherry and other experts say the reason is too little use of the vaccine among preschoolers.

CDC guidelines recommend that babies get their first measles shot at 15 months and a second between ages 4 and 6. Every child must be vaccinated to attend school.

However, in some cities only about half of all 2-year-olds have been vaccinated. It is these youngsters who catch the virus and then pass it on to infants.

Throughout history, measles epidemics have hit in periodic waves. The first of these outbreaks since the 1970s occurred in 1989, 1990 and 1991. And it was then that the new problem in newborns also became apparent.


Before routine vaccination, between 3 million and 4 million Americans got measles every year, and 500 died. But since vaccination started just over two decades ago, and until recently, only about 3,000 people got measles annually, and just one or two died of it.

But during the three-year outbreak, about 55,000 Americans got measles. The CDC counted 166 deaths, and 33 of them, or 20%, were in children under age 1.

This year, the epidemic has abated. The CDC expects there to be about 3,000 cases again. However, one big outbreak has occurred in Brownsville, Tex. About 1,000 people there have gotten measles, 45% of them under age 1.

“It’s very dramatic,” said Atkinson. “We are finding the same thing: This happens to kids whose mothers are young.”


Such outbreaks in the very young can take physicians by surprise. When an epidemic swept through Houston in the winter of 1988-89, many of the doctors had never seen a case of measles. Doctors were especially puzzled to have so many patients under 7 months old.

“Going back 29 years, we only had one child in that age group,” said Dr. David Matson of Baylor College of Medicine. But during this outbreak, 107 measles patients were admitted to Texas Children’s Hospital, and 22% were in their first 6 months of life.

Some of the most persuasive evidence that maternal vaccinations play a role in infant measles comes from a CDC investigation of an outbreak in New Jersey during the epidemic.

Dr. Mark Papania and others looked at families where infants were exposed to people with measles. They found that the babies of mothers born after 1968, when vaccination became common, were 3 1/2 times more likely to get measles than were infants of older mothers.


“It confirms our suspicion that the risk is increasing in this age group because of the changing distribution of maternal birth year,” said Papania. “As we go forward in time, mothers are more likely to have not been exposed to wild measles virus.”

The CDC estimates that at least 40% of babies are now born to vaccinated mothers, and this should near 100% by the end of the decade. So the problem of infant measles will probably only get worse as more vaccinated women reach motherhood.

One possible way to protect vulnerable infants from measles is to vaccinate them at younger ages, although this is not as simple as it sounds.

The vaccine simply won’t work if babies still have their mothers’ antibodies in their blood. The problem is guessing when the antibodies are gone, since no simple test shows this.


The current recommendation that the measles vaccine not be routinely given before age 15 months is based on studies done in the 1970s. Most babies then were born to mothers who had not been vaccinated, so they had high antibody levels.

The CDC already recommends vaccinating babies at 1 year old if they live in poor urban areas where the disease is especially common. No one knows how well the vaccine will work in babies under age 1 or whether they will need to have their shots repeated a year or two later. However, several experts said they expect the recommended age for routine vaccination to be lowered to at least a year and perhaps younger.

“A sensible age would be maybe 9 or 10 months,” predicted Dr. Henry Pabst of the University of Alberta. “That may be the solution eventually. At that age, you would probably have a good enough immune system in the infant to respond well.”

However, several in the field contend that the key to stopping infant measles is getting everybody vaccinated in early childhood, before they catch the disease and spread it. That could eliminate measles entirely.


“We became complacent,” said Dr. Edward O’Roarke of Children’s Hospital in Boston. “We can wipe out measles like we did smallpox. We lost track of the fact that we needed to get that last out in the bottom on the ninth, and we didn’t do it.”