Lower Pregnancy Risks Associated with HPV Vaccination in Women

Women vaccinated against human papillomavirus (HPV) were significantly less likely to have a range of adverse outcomes during pregnancy, according to a national case-control study from Sweden.

Among nearly 625,000 births from 2006 to 2023, women who had received a quadrivalent HPV shot had significantly lower odds of preterm birth (adjusted odds ratio [aOR] 0.95, 95% CI 0.91-0.99), very preterm birth (aOR 0.85, 95% CI 0.75-0.97), and spontaneous preterm birth (aOR 0.95, 95% CI 0.91-0.99) compared with those who were unvaccinated, reported Jiayao Lei, PhD, of Karolinska Institute in Stockholm, and colleagues.

Stronger Associations with Early Vaccination

Links were stronger when HPV vaccination occurred before age 17 for both preterm birth (aOR 0.90, 95% CI 0.85-0.95) and spontaneous preterm birth (aOR 0.89, 95% CI 0.84-0.95) compared with those who were unvaccinated.

“Our findings highlight the importance of timely HPV vaccination and suggest that its potential benefits may extend beyond cancer prevention to reproductive health,” Lei and co-author Zhongsong Zhang, a PhD student at Karolinska Institute, stated. “Although the observed differences were relatively modest at the individual level, they could translate into meaningful public health and economic benefits at the population level.”

Policy Implications

Given the results, policy and cost-effectiveness analyses should include HPV vaccination’s cancer prevention benefits and reductions in pregnancy-related complications and resulting lifelong healthcare costs.

The potential pregnancy advantages linked to earlier HPV vaccination may show that the shots deliver greater benefits when they’re administered before sexual debut and potential HPV exposure. “Vaccination at an earlier age may also allow women to benefit from this protection for a longer period before entering their reproductive years,” they noted.

Mechanisms Behind the Observed Outcomes

The reasons why HPV and pregnancy outcomes may be linked aren’t entirely understood, but two potential explanations were highlighted. HPV may interfere with embryonic development, leading to placental issues and greater preterm birth risk. Additionally, maternal vaccination could reduce the risk of embryonic HPV exposure and consequent pregnancy complications.

Research has also connected treatment for HPV-related high-grade cervical lesions with increased risks of preterm birth and other adverse pregnancy outcomes. In this study, 0.6% of vaccinated women and 3.7% of unvaccinated women had a diagnosis of high-grade cervical lesion before giving birth. After adjusting for high-grade lesions, the associations between HPV vaccination and preterm birth-related outcomes weakened.

This pattern suggests that preventing high-grade cervical lesions and subsequent cervical treatments may partly explain the observed associations, although the researchers cautioned that the analysis should be interpreted as exploratory.

Vaccine Recommendations

In the U.S., a two-dose series of the nine-valent HPV vaccine (Gardasil 9) is recommended by the American Academy of Pediatrics starting between the ages of 9 and 12 years. Recent research has suggested that a single shot may offer similar levels of protection.

The study included 624,713 singleton births in Sweden among nulliparous women aged 16 to 35 years. Among eligible births, 14.8% of women had quadrivalent HPV vaccination before pregnancy. The researchers excluded births from women whose first HPV vaccination was bivalent or nonavalent and matched each adverse pregnancy outcome case with up to 10 controls without the same adverse outcomes to counter confounding.

Pregnancy Outcomes Evaluated

Vaccinated women were significantly less likely to have preterm prelabor rupture of membranes (preterm PROM; aOR 0.93, 95% CI 0.87-1.00) or severe small for gestational age infants (aOR 0.92, 95% CI 0.87-0.97), while no significant differences were noted for PROM, stillbirth, or neonatal mortality. Women vaccinated prior to age 17 had significantly lower odds of preterm PROM (aOR 0.86, 95% CI 0.78-0.94) and severe small for gestational age infants (aOR 0.91, 95% CI 0.84-0.97) compared to the unvaccinated.

Study Limitations

Limitations included potential residual confounding from catch-up vaccination, prior HPV exposure, or variations in sexual or reproductive behaviors, particularly in women aged 17 and older. Differences in preventive measures for preterm birth could not be fully assessed.

Disclaimer: This content is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.

Fuente: https://www.medpagetoday.com/infectiousdisease/vaccines/123378