With the supply of HPV vaccines dwindling, doctors and researchers are concerned about what this means for the spread of the disease. According to recent projections, there won’t be a sufficient number of HPV vaccine doses available to meet global demand until at least 2024. However, new research may provide a possible solution to the HPV vaccine shortage.
In an OBGYN News article published on May 29, 2019, follow-up results from major phase 3 randomized controlled trials of bivalent HPV vaccine in Costa Rica and quadrivalent vaccine in India were shared. These trials deliver promising evidence that a single HPV dose could provide protection against infection for 11 years or more. Since children who receive the vaccine at the recommended age currently receive two doses, this could potentially double the existing supply.
In the initial trials, the effectiveness of a single dose was actually a secondary analysis from the data collected. Researchers didn’t set out to study a single-dose HPV vaccine option, but they followed up with subjects who ended up only receiving a single dose instead of completing the full vaccine schedule. Therefore, the results don’t support the use of a single-dose vaccine on a larger scale. Due to the promising results, however, other studies have been initiated to provide additional data that could lead to modifications to official vaccine recommendations.
Follow-up from these studies found that at four and seven years after a single dose was administered, the vaccine was just as effective as a two- or three-dose series in preventing the two most dangerous types of HPV (types 16 and 18). The same results were found 11 years after the initial dose.
HPV serum antibody levels also remained stable in the single-dose group over the course of 11 years. Although the antibody levels were significantly lower than in subjects who received the three-shot series of the vaccine, it appears that the risk for infection was not higher in the single-dose group. This may be due in part to the fact that cervical cancers take so long to develop, giving the antibodies ample time to fight it off.
Although some phase 4 vaccine effectiveness monitoring studies have shown a lower rate of effectiveness for a single-dose HPV vaccine, the data analysis methods for these trials have been criticized. By grouping children and young teens with subjects over the age of 17, who have a much higher likelihood of previous exposure to HPV through sexual contact, the results may be skewed. The vaccine does not clear existing infections or protect against any strain an individual has already been exposed to, so it’s unclear whether infections in these subjects took place before or after vaccination.
At HPV Hub, we look forward to the results from future trials that are specifically targeting the potential effectiveness of a single-dose HPV vaccine. In addition to making the vaccine much easier to administer, a one-dose series would stretch the current vaccine supply much further.
- HPV vaccine: Is one dose enough?: OBGYN News, 2019.