A large meteoritic event over Antarctica ca. 430 ka ago inferred from chondritic spherules from the Sør Rondane Mountains.

Large airbursts, the most frequent hazardous impact events, are estimated to occur orders of magnitude more frequently than crater-forming impacts. However, finding traces of these events is impeded by the difficulty of identifying them in the recent geological record. Here, we describe condensation spherules found on top of Walnumfjellet in the Sør Rondane Mountains, Antarctica. Affinities with similar spherules found in EPICA Dome C and Dome Fuji ice cores suggest that these particles were produced during a single-asteroid impact ca. 430 thousand years (ka) ago. The lack of a confirmed crater on the Antarctic ice sheet and geochemical and 18O-poor oxygen isotope signatures allow us to hypothesize that the impact particles result from a touchdown event, in which a projectile vapor jet interacts with the Antarctic ice sheet. Numerical models support a touchdown scenario. This study has implications for the identification and inventory of large cosmic events on Earth.

Microtektites, microkrystites, and spinels from a late pliocene asteroid impact in the southern ocean.

The properties of glassy spherules found in sedimentary deposits of a late Pliocene asteroid impact into the southeast Pacific are similar to those of both microtektites and microkrystites. These spherules probably formed from molten silicate droplets that condensed from an impact-generate vapor cloud. The spherules contain inclusions of magnesioferrite spinels similar to those in spherules found at the Cretaceous-Tertiary boundary, indicating that both sets of spherules are impact debris formed under similar physical and chemical conditions.

Microtektites and mass extinctions: evidence for a late devonian asteroid impact.

Glass spherules, similar to microtektites, have been found near the Frasnian-Famennian boundary (F/F) (Upper Devonian) at Senzeilles, Belgium, contemporaneous with one of the largest marine mass extinctions of the Phanerozoic. These spherules exhibit a wide range of compositions and display teardrop, dumbbell, and compound morphologies analogous to microtektites. In addition, they lack crystallites, have few or no vesicles, and have a low content of volatile material. These characteristics are supportive of an impact origin. The Siljan Ring (Sweden) and Charlevoix structure (Quebec,Canada) are candidate craters of this age. The presence of microtektites near the F/F boundary supports the hypothesis that an impact caused the Upper Devonian worldwide benthic mass extinctions.

Emplacement of cretaceous-tertiary boundary shocked quartz from chicxulub crater.

Observations on shocked quartz in Cretaceous-Tertiary (K-T) boundary sediments compellingly tied to Chicxulub crater raise three problems. First, in North America shocked quartz occurs above the main K-T ejecta layer. Second, shocked quartz is more abundant west than east of Chicxulub. Third, shocked quartz reached distances requiring initial velocities up to 8 kilometers per second, corresponding to shock pressures that would produce melt, not the moderate-pressure shock lamellae observed. Shock devolatilization and the expansion of carbon dioxide and water from impacted wet carbonate, producing a warm, accelerating fireball after the initial hot fireball of silicate vapor, may explain all three problems.

Coeval 40Ar/39Ar Ages of 65.0 Million Years Ago from Chicxulub Crater Melt Rock and Cretaceous-Tertiary Boundary Tektites.

(40)Ar/(39)Ar dating of drill core samples of a glassy melt rock recovered from beneath a massive impact breccia contained within the 180-kilometer subsurface Chicxulub crater in Yucatán, Mexico, has yielded well-behaved incremental heating spectra with a mean plateau age of 64.98 +/- 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the Chicxulub 1 well. The age of the melt rock is virtually indistinguishable from (40)Ar/(39)Ar ages obtained on tektite glass from Beloc, Haiti, and Arroyo el Mimbral, northeastern Mexico, of 65.01 +/- 0.08 Ma (mean plateau age for Beloc) and 65.07 +/- 0.10 Ma (mean total fusion age for both sites). The (40)Ar/(39)Ar ages, in conjunction with geochemical and petrological similarities, strengthen the recent suggestion that the Chicxulub structure is the source for the Haitian and Mexican tektites and is a viable candidate for the Cretaceous-Tertiary boundary impact site.

Seizures in the intrahippocampal kainic acid epilepsy model: characterization using long-term video-EEG monitoring in the rat.

OBJECTIVE: Intrahippocampal injection of kainic acid (KA) in rats evokes a status epilepticus (SE) and leads to spontaneous seizures. However to date, precise electroencephalographic (EEG) and clinical characterization of spontaneous seizures in this epilepsy model using long-term video-EEG monitoring has not been performed. MATERIALS AND METHODS: Rats were implanted with bipolar hippocampal depth electrodes and a cannula for the injection of KA (0.4 lg /0.2 ll) in the right hippocampus. Video-EEG monitoring was used to determine habitual parameters of spontaneous seizures such as seizure frequency, severity, progression and day-night rhythms. RESULTS: Spontaneous seizures were detected in all rats with 13 out of 15 animals displaying seizures during the first eight weeks after SE. A considerable fraction (35%) of the spontaneous seizures did not generalize secondarily. Seizure frequency was quite variable and the majority of the KA treated animals had less than one seizure per day. A circadian rhythm was observed in all rats that showed sufficient seizures per day. CONCLUSIONS: This study shows that the characteristics of spontaneous seizures in the intrahippocampal KA model display many similarities to other SE models and human temporal lobe epilepsy.

Prediction of recurrent disease by cytology and HPV testing after treatment of cervical intraepithelial neoplasia.

OBJECTIVE: To assess the role of human papillomavirus (HPV) testing and cytology as predictors of residual/recurrent disease after treatment of high-grade cervical intraepithelial lesions. METHODS: One hundred and thirty-eight women with cervical intraepithelial neoplasia (CIN) grade 2/3 lesion on biopsy were included in a prospective follow-up study in Belgium and Nicaragua. All women were treated with loop electrosurgical excision procedure (LEEP) and follow-up visits took place at 6 weeks, 6 months, 1 year and 2 years. During these visits, a Papanicolaou (Pap) smear test was taken, colposcopy was performed and specimens were collected for HPV testing. Cytology, high-risk (HR) HPV presence, persistent HR HPV infection and combinations of these tests at different time points during follow-up were correlated with histologically confirmed residual/recurrent disease. RESULTS: Thirteen patients (9%) developed residual/recurrent disease during follow-up. Abnormal cytology at 6 weeks after treatment was significantly correlated with residual/recurrent disease. Nine of thirty-seven patients with abnormal cytology at 6 weeks had recurrent disease versus three of seventy with a normal cytology [odds ratio (OR): 7.2; 95% confidence interval (CI): 1.8-28.5; P = 0.003). Sensitivity of this test was 75.0%, specificity 70.5%. Combining abnormal cytology and the presence of HR HPV within the first 6 months after treatment gave the best correlation with residual/recurrent disease: of the 54 women with abnormal cytology and/or HR HPV presence within the first 6 months, 11 developed residual/recurrent disease (OR 10.2; 95% CI: 2.2-48.3). Sensitivity of this combination was 84.6% and specificity 65.0%. CONCLUSION: Cytology remains the cornerstone in the early follow-up after LEEP for CIN lesions of the cervix. HPV testing can add value as it increases the sensitivity of cytology in concomitant testing within the first 6 months.

Natural history and clearance of HPV after treatment of precancerous cervical lesions.

AIM: To assess the clearance rate of human papillomavirus (HPV) after out-patient treatment of cervical intraepithelial neoplasia (CIN). METHODS AND RESULTS: A total of 122 Nicaraguan women with HPV DNA-positive and histologically confirmed CIN lesions were included in the study. Fifty-five patients with CIN1 and 67 with CIN2-3 were treated by cryotherapy and loop electrosurgical excision procedure (LEEP), respectively. Follow-up visits were scheduled at 6 weeks, 6 months, 1 year and 2 years. Investigations included cytology, HPV DNA testing and colposcopy/biopsy if needed. The clearance rate of HPV was calculated by multivariate logistic regression. Immediately after treatment, a pronounced decrease in presence of HPV was observed in both groups, with a significantly higher clearance in the LEEP group than in the cryotherapy group (P = 0.019). Subsequently, clearance continued over time and was similar between the cryotherapy group and the LEEP group (P = 0.73). Approximately the same detection rates were obtained for persistence of all HPV types and for high-risk types separately: 43.9, 37.6, 29.9 and 17.7% in the cryotherapy group and 24.9, 20.3, 15.3 and 8.4% in the LEEP group at 6 weeks, 6 months, 1 year and 2 years, respectively. CONCLUSIONS: Out-patient treatment of precancerous lesions of the cervix usually results in clearance of HPV. Both LEEP and cryotherapy are highly effective methods of eradicating HPV. HPV DNA testing may have added value in the follow-up of patients.

Comparison of pap smear, visual inspection with acetic acid, human papillomavirus DNA-PCR testing and cervicography.

OBJECTIVE: To assess the test qualities of four screening methods to detect cervical intra-epithelial neoplasia in an urban African setting. METHOD: Six hundred fifty-three women, attending a family planning clinic in Nairobi (Kenya), underwent four concurrent screening methods: pap smear, visual inspection with acetic acid (VIA), PCR for high risk human papillomavirus (HR HPV) and cervicography. The presence of cervical intra-epithelial neoplasia (CIN) was verified by colposcopy or biopsy. RESULT: Sensitivity (for CIN2 or higher) and specificity (to exclude any CIN or cancer) were 83.3% (95% CI [73.6, 93.0]) and 94.6% (95% CI [92.6, 96.5]), respectively, for pap smear; 73.3% (95% CI [61.8, 84.9]) and 80.0% (95% CI [76.6, 83.4]) for VIA; 94.4% (95% CI [84.6, 98.8]) and 73.9% (95% CI [69.7, 78.2]) for HR HPV; and 72.3% (95% CI [59.1, 85.6]) and 93.2% (95% CI [90.8, 95.7]) for cervicography. CONCLUSION: The pap smear had the highest specificity (94.6%) and HPV testing the highest sensitivity (94.4%). The visual methods, VIA and cervicography, were similar and showed an accuracy in between the former two tests.

Vaginal lavage with chlorhexidine during labour to reduce mother-to-child HIV transmission: clinical trial in Mombasa, Kenya.

OBJECTIVES: To evaluate the effect of vaginal lavage with diluted chlorhexidine on mother-to child transmission of HIV (MTCT) in a breastfeeding population. METHODS: This prospective clinical trial was conducted in a governmental hospital in Mombasa, Kenya. On alternating weeks, women were allocated to non-intervention or to intervention consisting of vaginal lavage with 120 ml 0.2% chlorhexidine, later increased to 0.4%, repeated every 3 h from admission to delivery. Infants were tested for HIV by DNA polymerase chain reaction within 48 h and at 6 and 14 weeks of life. RESULTS: Enrolment and follow-up data were available for 297 and 309 HIV-positive women, respectively, in the non-lavage and the lavage groups. There was no evidence of a difference in intrapartum MTCT (17.2 versus 15.9%, OR 0.9, 95% CI 0.6-1.4) between the groups. Lavage solely before rupture of the membranes tended towards lower MTCT with chlorhexidine 0.2% (OR 0.6, 95% CI 0.3-1.1), and even more with chlorhexidine 0.4% (OR 0.1, 95% CI 0.0-0.9). CONCLUSION: The need remains for interventions reducing MTCT without HIV testing, often unavailable in countries with a high prevalence of HIV. Vaginal lavage with diluted chlorhexidine during delivery did not show a global effect on MTCT in our study. However, the data suggest that lavage before the membranes are ruptured might be associated with a reduction of MTCT, especially with higher concentrations of chlorhexidine.

Exposure to HIV-1 during delivery and mother-to-child transmission.

BACKGROUND: The correlation between the presence of HIV-1 in maternal cervicovaginal secretions and in the infant's oro-pharyngal secretions at birth, and mother-to-child HIV transmission (MTCT) were examined to obtain a better understanding of its mechanism. METHODS: Women without medical and obstetrical complications, living within a reasonable distance of the government hospital in Mombasa, Kenya, were recruited after informed consent. Maternal and infant characteristics were collected. Polymerase chain reaction was used to detect HIV-1 in cervico-vaginal and oro-pharyngal secretions. Infants were tested for HIV-1 by polymerase chain reaction within 48 h and at 6 weeks after delivery. RESULTS: Between April 1998 and April 1999, 228 woman-infant pairs were included in the study. HIV-1 DNA in cervico-vaginal secretions was independently associated with HIV-1 maternal viral load and with infant birth-weight, whereas HIV-1 RNA was associated with maternal viral load and maternal age. HIV-1 DNA in the oropharyngal secretions was also independently associated with maternal viral load. MTCT rate at the age of 6 weeks was 23.6%. Intrapartum and early postpartum HIV transmission was independently associated with maternal viral load [adjusted odds ratio (OR), 1.6; 95% confidence interval (CI),1.0-2.7], detection of HIV-1 RNA in cervico-vaginal secretions (adjusted OR, 3.2; 95% CI, 1.5-7.3) and of HIV-1 DNA in oro-pharyngeal secretions (adjusted OR, 3.2; 95% CI, 1.1-9.0). DISCUSSION: As far as is known, this is the first study showing that infant exposure to HIV-1 in the birth canal and the presence of HIV-infected cells in the infant's oropharyngeal cavity are independently associated with intrapartum and early postpartum MTCT. It supports the hypothesis that MTCT could occur through the oral route.

Tektite-bearing, deep-water clastic unit at the Cretaceous-Tertiary boundary in northeastern Mexico.

The hypothesis of Cretaceous-Tertiary (K-T) boundary impact on Yucatán, Mexico, predicts that nearby sites should show evidence of proximal impact ejecta and disturbance by giant waves. An outcrop along the Arroyo el Mimbral in northeastern Mexico contains a layered clastic unit up to 3 m thick that interrupts a biostratigraphically complete pelagic-marl sequence deposited at more than 400 m water depth. The marls were found to be unsuitable for determining magnetostratigraphy, but foraminiferal biostratigraphy places the clastic unit precisely at the K-T boundary. We interpret this clastic unit as the deposit of a megawave or tsunami produced by an extraterrestrial impact. The clastic unit comprises three main subunits. (1) The basal "spherule bed" contains glass in the form of tektites and microtektites, glass spherules replaced by chlorite-smectite and calcite, and quartz grains showing probable shock features. This bed is interpreted as a channelized deposit of proximal ejecta. (2) A set of lenticular, massive, graded "laminated beds" contains intraclasts and abundant plant debris, and may be the result of megawave backwash that carried coarse debris from shallow parts of the continental margin into deeper water. (3) At the top, several thin "ripple beds" composed of fine sand are separated by clay drapes; they are interpreted as deposits of oscillating currents, perhaps a seiche. An iridium anomaly (921 +/- 23 pg/g) is observed at the top of the ripple beds. Our observations at the Mimbral locality support the hypothesis of a K-T impact on nearby Yucatán.

Proximal impact deposits at the Cretaceous-Tertiary boundary in the Gulf of Mexico: a restudy of DSDP Leg 77 Sites 536 and 540.

Restudy of Deep Sea Drilling Project Sites 536 and 540 in the southeast Gulf of Mexico gives evidence for a giant wave at Cretaceous-Tertiary boundary time. Five units are recognized: (1) Cenomanian limestone underlies a hiatus in which the five highest Cretaceous stages are missing, possibly because of catastrophic K-T erosion. (2) Pebbly mudstone, 45 m thick, represents a submarine landslide possibly of K-T age. (3) Current-bedded sandstone, more than 2.5 m thick, contains anomalous iridium, tektite glass, and shocked quartz; it is interpreted as ejecta from a nearby impact crater, reworked on the deep-sea floor by the resulting tsunami. (4) A 50-cm interval of calcareous mudstone containing small Cretaceous planktic foraminifera and the Ir peak is interpreted as the silt-size fraction of the Cretaceous material suspended by the impact-generated wave. (5) Calcareous mudstone with basal Tertiary forams and the uppermost tail of the Ir anomaly overlies the disturbed interval, dating the impact and wave event as K-T boundary age. Like Beloc in Haiti and Mimbral in Mexico, Sites 536 and 540 are consistent with a large K-T age impact at the nearby Chicxulub crater.

Partner notification of pregnant women infected with syphilis in Nairobi, Kenya.

We examined partner notification among syphilitic pregnant women in Nairobi. At delivery, 377 women were found to be rapid plasma reagin (RPR) reactive. Data were available for 94% of the partners of women who were tested during pregnancy; over 67% of the partners had received syphilis treatment while 23% had not sought treatment mainly because they felt healthy. Six per cent of the women had not informed their partners as they feared blame and/or violence. Adverse pregnancy outcome was related to lack of partner treatment during pregnancy (7% versus 19%, odds ratio (OR) 3.0, 95% confidence interval (CI) 0.9-10.0). Our data suggest that messages focusing on the health of the unborn child have a positive effect on partner notification and innovative and locally adapted strategies for partner notification need more attention.

Declining syphilis prevalence in pregnant women in Nairobi since 1995: another success story in the STD field?

Untreated maternal syphilis during pregnancy will cause adverse pregnancy outcomes in more than 60% of the infected women. In Nairobi, Kenya, the prevalence of syphilis in pregnant women of 2.9% in 1989, showed a rise to 6.5% in 1993, parallel to an increase of HIV-1 prevalence rates. Since the early 1990s, decentralized STD/HIV prevention and control programmes, including a specific syphilis control programme, were developed in the public health facilities of Nairobi. Since 1992 the prevalence of syphilis in pregnant women has been monitored. This paper reports the findings of 81,311 pregnant women between 1994 and 1997. A total of 4244 women (5.3%) tested positive with prevalence rates of 7.2% (95% CI: 6.7-7.7) in 1994, 7.3% (95% CI: 6.9-7.7) in 1995, 4.5% (95% CI: 4.3-4.8) in 1996 and 3.8% (95% CI: 3.6-4.0) in 1997. In conclusion, a marked decline in syphilis seroprevalence in pregnant women in Nairobi was observed since 1995-96 (P<0.0001, Chi-square test for trend) in contrast to upward trends reported between 1990 and 1994-95 in the same population.

PIP: This study presents the trend in syphilis prevalence among 81,311 pregnant women in Nairobi, Kenya, from 1994 to 1997. Clinic nurses performed syphilis serology using a rapid plasma reagin (RPR) card test in 10 NCC clinics and Chi square; these were used to study trends over time. Results showed that a total of 4244 women (5.3%) tested positive with prevalence rates of 7.2% (95% CI: 6.7-7.7) in 1994, 7.3% (95% CI: 6.9-7.7) in 1995, 4.5% (95% CI: 4.3-4.8) in 1996, and 3.8% (95% CI: 3.6-4.0) in 1997. Thus, a significant decrease in syphilis seroprevalence among pregnant women in Nairobi was observed since 1995-96, by contrast with the rising trend in syphilis prevalence reported in 1990 and 1994-95 in the same population. This decline was attributable in large part to the syphilis control program initiated in Nairobi in June 1992, which focused on sexual behavior modifications, changes in health care seeking behavior and improved health care services.

Anti-epileptogenesis research: the clinical relevance.

In recent years, different research lines have examined the epileptogenic process in order to understand the different stages in this process, and with the hope that early recognition and intervention could prevent chronic epilepsy in patients with epileptic seizures. In animals, acquired epilepsy is studied most commonly with kindling models, status epilepticus models and traumatic brain injury models. Molecular genetic studies substantially help to understand age-specific channel and receptor abnormalities. Major progress has been made in recent years and we are now waiting for the first large scale multi-center clinical trials that test the possible anti-epileptogenic properties of anti-epileptic drugs or other compounds in well defined patient groups. In clinical practice, a structured diagnostic work-up in all patients with recurrent seizures is a first and necessary step in the recognition of patients at risk for developing chronic and refractory epilepsy.

Integration of cervical screening in family planning clinics.

OBJECTIVES: To assess the suitability of cervical cancer screening in family planning (FP) clinics and the relevance for women's health. METHODS: A survey was done on clients visiting the clinics of the Family Planning Association of Kenya (FPAK). Client characteristics, age, screening status and PAP smear results were registered. In-depth interviews were held with a limited number of staff and clients. RESULTS: In 1999, 38052 clients visited FPAK clinics, 43.5% were younger than 30 years old. More than 10000 cervical smears were taken. A total of 4.5% of the smears were abnormal, including 1.5% high-grade squamous intraepithelial lesions (HSIL) and 0.2% invasive cancers. The clinics were well prepared to provide high quality screening services. Patients and staff had a positive view on screening. CONCLUSIONS: Providing cervical cancer screening in FP clinics is beneficial for the clients but is unlikely to have an impact on the epidemiology of cervical cancer morbidity as FP services reach only a small percentage of the women who are most at risk. Measures to reach more and older women could assure a larger impact.

Risk factors for human papillomavirus and cervical precancerous lesions, and the role of concurrent HIV-1 infection.

OBJECTIVES: To identify risk factors for human papillomavirus (HPV) infection and squamous intraepithelial lesions (SIL) of the cervix, and to measure the impact of concurrent HIV-1 infection. METHODS: Women were studied at a family planning clinic in Nairobi, Kenya. Demographic and historical information was obtained using a semi-structured questionnaire and specimens were collected for sexually transmitted diseases (STDs), HPV, cervical cytology, and HIV-1 testing. RESULTS: HPV was detected in 87 of 513 women (17%), including 81 (93%) oncogenic types (16, 18, 31, 33 and others) and six (7%) non-oncogenic types (6 and 11). HIV-1 prevalence was 10%. HPV detection was associated with HIV-1 infection [adjusted odds ratio (aOR) 3.9, 95% confidence interval (CI), 2.0-7.7], sexual behavior indicators including the number of sex partners and inflammatory STDs, as well as the number of pregnancies (0 or 1 vs. > or = 3, aOR 0.4; 95% CI, 0.2-0.9). SIL was detected in 61 women (11.9%), including 28 (46%) with low-grade lesions (LSIL) and 33 (54%) with high-grade lesions (HSIL). HPV infection was strongly associated with HSIL (OR 14.9; 95% CI, 6.8-32.8). In a multivariate model predictors of HSIL included HIV-1 serpositivity (aOR 4.8; 95% CI, 1.8-12.4), the number of lifetime sex partners (0-1 vs. > or = 4; aOR 3.8; 95% CI, 1.1-13.5), and older age (< 26 vs. > 30; OR 3.9; 95% CI, 1.1-13.6). An analysis stratified by HIV-1 showed a stronger association between HPV and HSIL in HIV-1 negative women (OR 17.0; 95% CI, 6.4-46.3) then in HIV-1 positive women (OR 4.5; 95% CI, 0.8-27.4). CONCLUSION: Our results indicate that HSIL and even invasive cancer are highly prevalent in this setting of women on reproductive age considered to be at low risk for STDs, suggesting that routine Pap smear screening may save lives.

Sexual behaviour and contraceptive use among youth in the Balkans.

OBJECTIVES: To assess sexual and health seeking behaviour related to contraception among high school students in Bosnia (Sarajevo), the FYR of Macedonia (Skopje), and Serbia and Montenegro (Belgrade and Podgorica). METHODS: A standardized questionnaire was self-administered by 2150 urban high school students. Multiple logistic regression analyses accounting for within-class correlation were applied to identify determinants of sexual behaviour, and the use of contraception and sexual and reproductive health (SRH) care. RESULTS: In this group of youth with a mean age of 16.7 years, 41.3% of the boys and 20.8% of the girls had already experienced sexual intercourse. Mean age at sexual debut differed between sexually active boys (15.5) and girls (16.3). A condom was used at first sex by 73.7% of the boys and by 69.0% of the girls. Condoms were consistently used during sexual intercourse with the current or last partner by 64.3% of the boys and 48.5% of the girls. Oral contraception was resorted to by 0.0% (Macedonia) to 10.6% (Bosnia) of sexually active girls. One third of sexually active girls and 18.0% of sexually active boys had ever refrained from seeking medical advice on SRH despite feeling the need for it, mainly because of feelings of shame, fear and insecurity. TV or radio and friends were mostly mentioned as useful sources of information on contraceptives. CONCLUSIONS: Age at sexual debut and the proportion of sexually active youth in these Balkan states do not differ from those in other parts of Europe. However, declining condom use after sexual initiation is not compensated by having recourse to other contraceptive methods, as seen in some West-European countries. The role of mass media in dissemination of information and tackling barriers to SRH care should be explored.

Human papillomavirus and HPV vaccines: a review.

Cervical cancer, the most common cancer affecting women in developing countries, is caused by persistent infection with "high-risk" genotypes of human papillomaviruses (HPV). The most common oncogenic HPV genotypes are 16 and 18, causing approximately 70% of all cervical cancers. Types 6 and 11 do not contribute to the incidence of high-grade dysplasias (precancerous lesions) or cervical cancer, but do cause laryngeal papillomas and most genital warts. HPV is highly transmissible, with peak incidence soon after the onset of sexual activity. A quadrivalent (types 6, 11, 16 and 18) HPV vaccine has recently been licensed in several countries following the determination that it has an acceptable benefit/risk profile. In large phase III trials, the vaccine prevented 100% of moderate and severe precancerous cervical lesions associated with types 16 or 18 among women with no previous infection with these types. A bivalent (types 16 and 18) vaccine has also undergone extensive evaluation and been licensed in at least one country. Both vaccines are prepared from non-infectious, DNA-free virus-like particles produced by recombinant technology and combined with an adjuvant. With three doses administered, they induce high levels of serum antibodies in virtually all vaccinated individuals. In women who have no evidence of past or current infection with the HPV genotypes in the vaccine, both vaccines show > 90% protection against persistent HPV infection for up to 5 years after vaccination, which is the longest reported follow-up so far. Vaccinating at an age before females are exposed to HPV would have the greatest impact. Since HPV vaccines do not eliminate the risk of cervical cancer, cervical screening will still be required to minimize cancer incidence. Tiered pricing for HPV vaccines, innovative financing mechanisms and multidisciplinary partnerships will be essential in order for the vaccines to reach populations in greatest need.