PCVs Effective, But Efficacy Wanes Over Time

New research from Australia supports the use of booster doses of the pneumococcal conjugate vaccine, but it shows overall effectiveness is high.

Sanjay Jayasinghe, MSc, PhD

New research confirms that both the 7-valent and 13-valent versions of the pneumococcal conjugate vaccine (PCV) are highly effective. However, it also finds the efficacy wanes over time, bolstering the case for a booster dose.

The new study, from the University of Sydney, in Australia, looked at the effectiveness PCVs in preventing disease in Australian children. The study covered the years 2005 through 2014 and included both the 7-valent version and the 13-valent version, which came into use in Australia in 2011.

Since 2005, Australia has been using a “3+0” dosing schedule, with doses given at 2, 4, and 6 months of age. All other high-income countries in the world use a 2+1 or 3+1 regimen, with the primary doses followed by a booster shot at around 1 year of age.

First author Sanjay Jayasinghe, MBBS, MSc, PhD, of the University of Sydney’s National Centre for Immunisation Research and Surveillance for Vaccine Preventable Diseases, told Contagion® that the study demonstrated the effectiveness of PCVs.

“First and foremost, I think it is important to emphasize that our study confirmed for both PCV7 and PCV13 remarkably high effectiveness against invasive pneumococcal disease (IPD) caused by serotypes covered by the vaccine, in the first year of life,” he said. “This is evident in the large reductions in the disease burden seen in the age groups eligible for vaccination.”

Although the study found both vaccines are effective, it also found that they were less effective over time. Children in the study were found to be 5 times as likely to contract IPD when their most recent vaccine dose was more than 2 years old, as opposed to those who had been vaccinated within the past year. Overall, vaccine effectiveness for the 13-valent version dropped by 17% between 12 and 24 months after the completion of the 3-dose schedule, and by an additional 46% between 24 and 36 months.

Dr. Jayasinghe said that loss of effectiveness is something not previously understood. As a result of these data, Australian regulators last September voted to switch from a 3+0 to a 2+1 regimen.

Although Jayasinghe said his research should be taken into account when countries reconsider vaccine schedules, he said each country needs to tailor its approach to country-specific factors.

Cynthia G. Whitney, MD, PhD

In a commentary on the study, Cynthia G. Whitney, MD, PhD, chief of the Respiratory Diseases Branch, of the National Center for Immunization and Respiratory Diseases, part of the US Centers for Disease Control and Prevention, cautioned that “more data are needed from other settings where disease transmission, disease risk, and ability to deliver vaccine doses might be quite different than that seen in Australia.”

The question can be complicated, Dr. Whitney said. Since 1-year-olds are considered the most common sources of pneumococcal transmission, the booster shot at 12 months would seemingly provide a boost in prevention right when it’s needed. But she said most countries end up dropping 1 of the 3 primary doses when they add a booster shot. That could leave children under 1 year of age more vulnerable.

Dr. Whitney told Contagion® the only countries now without a PCV booster shot recommendation are middle- and low-income countries. One reason a booster shot might not be a fit for every country is that in some cases it can require a special visit to a clinic.

“Some of these countries do not already have routine health visits for vaccination around the time a booster would be given, so it’s possible that many children would miss the booster dose if the schedule was changed to include 1 (booster),” she said. “They would have to adapt their programs to ensure children come in for the booster.