The dance of the pneumococcal serotypes

New data reveals a dramatic decline in the rates of invasive disease caused by the serotypes that had been protected against by vaccines

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New data shows how, historically, the prevalence of particular pneumococcal strains rises and falls in line with changes to the vaccination schedule, showing that the vaccines are working as planned.

The research, presented at the International Symposium on Pneumococci and Pneumococcal Diseases conference in Melbourne, tracked the changes in pneumococcal serotypes in people aged 65 or over. 

The data revealed a dramatic decline in the rates of invasive disease caused by the serotypes that had been protected against by vaccines. 

The timing of the changes in the prevalence of different serotypes closely reflected the addition of different pneumococcal vaccines onto the National Immunisation Program, including the seven-valent vaccine (7vPCV) for infants in 2005, the 13-valent vaccine for infants (13vPCV) in 2011, and the 23-valent vaccine (23vPPV) for people aged 65 and over in 2005.

Universal immunisation of children against the seven (and then 13) serotypes of pneumococcal seemed to knock these strains out of circulation, conferring substantial protection against these serotypes in older adults.

“Because the vaccine has been so effective in children, it’s offering protection or herd protection to older people,” Associate Professor John Litt, a GP affiliated with Flinders University, South Australia who co-authored the research poster, said.

“It has been so effective that we are not seeing many of those 13 serotypes, and the government is actually having a long, hard look at [whether to change the vaccine for] older adults.”

As expected, the pneumococcal serotypes that have not been immunised against are making up a larger proportion of invasive disease cases, reflecting serotype replacement.

And the direct impact of 23vPPV was evident in the significantly lower rate of growth in invasive disease attributable to its 11 exclusive serotypes, the authors said. 

Rates of pneumococcal vaccination were very high among infants (around 93%), but was poor in older adults, with only around 54% coverage.

“It’s quite safe to give the pneumococcal vaccine with the flu vaccine; the two of them won’t have any impact on each other,” Professor Litt said. 

“The flu vaccine has arrived in general practices so now is the time to say, ‘look, you’re having a flu shot, I can give you a pneumococcal shot if you haven’t had one’.”