07 December 2012

HPV Vaccine Doesn't Increase Sexual Activity

The intimate contact involved in sexual activity allows a variety of diseases to be transmitted, including several that are transmitted only through sexual activity or other exchanges of bodily fluids, such as through the sharing intravenous drug administration needles.

Using condoms can prevent the transmission of most sexually transmitted diseases, but they aren't particularly effective at stopping the transmission of the virus called HPV which causes cervical cancer and genital warts in some subset of the people who are infected (often much later).  Social conservatives like to make this point, because it provides a solid reason not to have premarital sex that birth control methods and condoms can't undermine.

Then, a safe and effective vaccine that stops the more common and virulent forms of the HPV virus was invented.  Would the ability to be vaccinated against the only STD that a condom can't prevent the transmission of cause rational young people to engage in more sexual behavior?

The answer is no.  HPV vaccination had no effect on sexual activity in a study that compared to a control group.
Since the introduction of Gardasil, there have been concerns—raised both in peer-reviewed literature and the popular media—that use of the vaccine might lead to increased sexual activity, due in part to the mistaken belief that Gardasil protects against pregnancy and sexually transmitted diseases other than HPV. . . . "We saw no increase in pregnancies, sexually transmitted infections or birth control counseling – all of which suggest the HPV vaccine does not have an impact on increased sexual activity.". . . 
The study included 1,398 girls ages 11 who were members of the Kaiser Permanente health plan in Georgia in 2006 and 2007, during the first 18 months after the Gardasil vaccine became available. Of this group, 493 girls received at least one dose of the HPV vaccine during the study period. The comparison group included 905 girls who received other recommended vaccines but not the HPV vaccine. Researchers followed both groups of girls for up to three years to assess whether they had been tested for or diagnosed with a sexually transmitted infection (STI), had taken a pregnancy test, and had been counseled about contraceptives. 
About 10 percent of the girls in the study, both those who received the vaccine and those who did not, had one or more of these outcomes. The average age of testing, diagnosis, or counseling was about 14.5. Only eight girls, or less than 1 percent, were diagnosed with an STI or had a positive pregnancy test. Girls who received the HPV vaccine did not have a statistically higher rate of testing, diagnosis, or counseling compared to those who did not receive the vaccine.
Teen Births At Near Record Lows

In fact, teen pregnancy rates in the United States are lower than they have been almost any time in recorded history, except during World War II, when many young men were abroad serving in the military. 

Births to teenaged mothers are down 44% over twenty years for U.S. born teens and 43% over twenty years for foreign born teens over the last twenty years. "The 2010 rate was . . . 64 percent lower than the all-time high level of 96.3 recorded during the baby boom year of 1957," during the time period since 1920 over which accurate birth records have been maintained by the government. Of course, until not so long ago, for example, during the peak of the Baby Boom in 1957, a far larger proportion of teen mothers were newly married and trying to have children.

The decline has been similar across racial and ethnic lines: 54% for non-Hispanic white teens, 44% for non-Hispanic black teens, 53% for Hispanic teens, 46% for Native American teens, and 40% of Asian American teens.  

If the teen birth rates observed in 1991 had not declined through 2010 as they did, there would have been an estimated 3.4 million additional births to teens during 1992–2010." This would have been a difference of about 1% of the entire population of the United States.
Teen mothers account for a higher share of births to U.S.-born women (11% in 2010) than to foreign-born women (5%)[.]

Teen birth rates are two and half times or more higher in many Southern States than they are in many New England States: "The birth rate for teenagers ranged from 15.7 in New Hampshire to 55.0 in Mississippi in 2010."

This year's trends continue those of a year ago reported at this blog.

Unmarried Mothers More Common

The proportion of women giving birth who aren't married has reached historically high levels (overall 41% of U.S. births compared to 28% twenty years ago), but their profiles are very different from the unmarried women giving birth of a few few decades ago.

Today, unmarried mothers tend to be in their twenties or thirties, rather than their teens. These women are often not poor. These women often have stable relationships with the fathers of their children, although not nearly as often as in Sweden, for example. Their pregnancies are frequently not "accidents." There is simply less of a sense in our culture that it is necessary or beneficial to get married before having children.

There are big differences in unmarried birth rates along racial and ethnic lines, however. Foreign born women are less likely to be unmarried than U.S. born women in every racial and ethnic category.

Looking at births to foreign-born mothers by race and ethnicity, the highest share to unmarried mothers is among Hispanics (50%), followed by blacks (38%), whites (13%) and Asians (12%). Among births to U.S.-born women, the highest share to unmarried mothers is among blacks (78%), followed by Hispanics (58%), Asians (31%) and whites (30%).
Eight out of ten U.S. born black mothers, and six out of ten U.S. born Hispanic mothers are not married, as are about half of foreign born Hispanic mothers, and about four in ten foreign born black mothers. About three in ten U.S. born Asian and white mothers, and about one in eight foreign born Asian and white mothers, are not married.

Marriage Is Becoming A Two Track Institution

Marriage rates show a strong class bias. College educated mothers are much more likely to be married and much less likely to get divorced, than mothers who have only graduated from high school or mothers who are high school dropouts. The women who are least likely to marry also tend to be the women who are most likely to divorce.

Only 4% of the children of mothers with college degrees are born out of wedlock. And the divorce rate among college-educated women has plummeted. Of those who first tied the knot between 1975 and 1979, 29% were divorced within ten years. Among those who first married between 1990 and 1994, only 16.5% were.

At the bottom of the education scale, the picture is reversed. Among high-school dropouts, the divorce rate rose from 38% for those who first married in 1975-79 to 46% for those who first married in 1990-94. Among those with a high school diploma but no college, it rose from 35% to 38%. And these figures are only part of the story. Many mothers avoid divorce by never marrying in the first place.

Marriage has all but disappeared as an institution in poor and working class black communities (in part because so many young men in those communities are incarcerated, unemployed or marginally employed), while it remains healthy among upper middle class whites and Asian Americans.

The shift is fairly recent. For example, in 1950, there was no black-white racial disparity in marriage rates. The trend extends to Europe as well, although not to Japan, where very few mothers are unmarried.

Falling Birth Rates Generally

Overall birth rates are lower than they have ever been in the entire history of the United States, among almost every demographic group. The exception has been among middle class women over the age of thirty-five, where assisted reproduction technologies have boosted birth rates and higher levels of education and career involvement have encouraged women to defer having children. 

The report linked on this year's trends notes that: "The overall U.S. birth rate peaked most recently in the Baby Boom years, reaching 122.7 in 1957, nearly double today’s rate." The birth rate in 1920 was about the same as it was at the peak of the Baby Boom. It declined during the Great Depression and World War II, rose during the Baby Boom years after World War II, declined rapidly after that until the mid-1970s, and then has stablized and declined very gradually since then.

Complete and accurate birth rate records go back only to 1920, but birth rates were consistently so much higher than that no one seriously believes that there were any years prior to 1920 when the United States had lower birth rates than it does now. 

In the wake of the financial crisis, birth rates have fallen particularly rapidly for women who were born in Mexico and immigrated (legally or illegally) to the United States. In the most recent year, their birth rate was down 23% in a single year.

Net migration from Mexico to the United States (legal and illegal combined) has been zero since the financial crisis, and this trend means that Mexican immigrants have, on average, lived in the United States for longer periods of time. Some analysts think that immigrants who have lived in the United States for longer periods of time are more likely to assimilate U.S. norms about how many children to have which has contributed to lower birth rates for immigrant women. Birth rates in Mexico has also declined significantly over the last couple of decades.

The low overall birth rate in the last few years is largely an artifact of hard economic times following the financial crisis. Everyone expects that it will rebound somewhat as the economy recovers.

But, the trend towards lower fertility rates for teenagers, black women, Hispanic women and poor women has been a consistent one over roughly the past twenty years, when violent crime and other negative social indicators were at a peak.  Starting in the last decade or so, for the first time in a century or two, more affluent women are having more children than less affluent women.

In the last twenty years, birth rates overall have fallen 10%, but the drop was 22% for foreign born women, 29% for U.S. born black women, 21% for U.S. born Hispanic women, and 25% for U.S. born Asian American women. For U.S. born white women the drop was 5%. Births to both U.S. born and foreign born women aged 20-34 are down over the last twenty years, but births to U.S. born women aged 35 and older are up 18% and births to foreign born women aged 35 and older are up 14% over the last twenty years. Even among women aged 35 and older, births have fallen over the last twenty years for foreign born Hispanic women and U.S. born black women.

Resulting Population Trends

The birth rate in the U.S.is still higher than countries like Italy and Russia and Japan (in those countries birth rates are as much as a third below replacement levels), in part due to large numbers of immigrant women with higher fertility levels. But, like all countries in the developed world, the U.S. has low and falling birth rates.

The U.S. birth rate is currently at about 10% below replacement levels, and the U.S. population would be declining right now if it weren't for the high levels of immigration it has had for the past few decades and continues to enjoy. In 1960, 4% of children in the U.S. had mothers who were not born in the U.S., in 2010 the figure was 21%, rivaling levels last seen in 1910.

Abortion In The United States Is Increasingly Rare.

Abortion utilization is not driving these trends. Abortion rates have declined, more or less proportionately with falling birth rates (or perhaps a bit more) to the lowest levels since Roe v. Wade, 410 U.S. 113 (1973). Prior to 1973, abortion was illegal in many states.

The abortion rate in 2009, the most recent year for which official data are available, was at an all time, pro-Roe v. Wade low down 5% from 2008.

This wasn't only due to a falling number of pregnancies. The "number of pregnancies terminated for every 1,000 live births. . . dropped too, from 232 in 2008 down to 227 in 2009, a 2 percent decrease."

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