CDC Study Suggests Vaccination Offers More Protection Against Covid Than Prior Infection
By Dr. William Schaffner
Hospital infection rates often lag behind viral threats, like flu, which have become increasingly prevalent. But after a three-year trial, a team of researchers at the Centers for Disease Control and Prevention found that routine clinical use of the HPV vaccine significantly reduced HPV infections among HPV-infected women in the general population.
The new study has come from the largest trial of human papillomavirus (HPV) vaccination to date, involving more than 3,600 women in 78 U.S. cities.
About half of those women received a six-month course of the vaccine (the primary version of the combined dose), and the other half were vaccinated with a three-month course. HPV vaccines are approved to prevent HPV infections; however, the study also found that HPV infections were significantly reduced in some of the women vaccinated.
The authors evaluated three strains of HPV virus in 25% of the women enrolled in the study, specifically, HPV 16 and HPV 18.
Previous studies have looked at whether vaccinating one or two strains of HPV cuts the risk of getting cervical cancer. However, no study had looked at whether administering both strains of HPV at once prevented further HPV infections in women who had already been infected.
The new trial reveals that the vaccine provides more protection against the strains of HPV linked to cervical cancer and other genital infections.
The study included about 30% of the women who got the HPV vaccine; the remainder of the women were HPV-uninfected control subjects, and other patients in the general population. About one quarter of the women enrolled had already received their first dose of the vaccine and the rest had not.
When the study participants left the study, researchers estimated the severity of their HPV infections based on the frequency of their genital warts. On average, women in the vaccine group were infected with 3.4 strains of HPV, which were more than twice as many strains as women in the control group, who were infected with 2.7 strains.
In women who were on two- and three-year courses of HPV vaccination, their frequency of new infection fell by nearly half. But the chance of getting new infections of any type of HPV increased by nearly 18%. This pattern was seen in nearly 90% of women who were vaccinated, even after adjusting for age, race, sex, income, and education.
HPV vaccination appears to reduce not only the risk of developing new infections, but also the chance of infections that evolve into more serious infections.
The study findings do not necessarily mean that the HPV vaccine works by itself in preventing infections from their most severe form, said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center and Vanderbilt University School of Medicine.
“The high initial incidence we saw indicates that there were the potential for inflammatory response at infection, but the vaccines did not work on immunity to that response,” Schaffner said. “So the vaccine could not provide some protection against an immune response.”
However, he noted that as more epidemiological studies of the HPV vaccine are conducted, it will become clear how effective it really is. The study authors expect to continue to see whether the vaccinations reduce more serious complications that often come with infection.
It may take the findings from this clinical trial to prompt changes in the way that health care providers handle such cases in order to improve the long-term effectiveness of the vaccine, said Dr. Leslie Csanka, an infectious disease specialist at Kaiser Permanente Oakland.
“In the next six months, we expect to see results from other studies evaluating clinical outcomes related to the HPV vaccine,” Csanka said.
The study appears in the Feb. 18 issue of the Journal of the American Medical Association.
This story was provided by Kaiser Health News, an editorially independent program of the Kaiser Family Foundation.