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Pneumococcal vaccines have been available for 40 years in various forms. These vaccines inhibit invasion by Streptococcus pneumoniae that cause serious clinical diseases, including bacteremic pneumococcal pneumonia and meningitis.^1,2 

The 13-valent pneumococcal conjugate vaccine (PCV13), which was introduced in March 2010, has performed as anticipated, but it hasn鈥檛 obviated the need for continued population surveillance of invasive pneumococcal disease (IPD), according to a study conducted in Olmsted County, Minnesota, by investigators at Mayo Clinic.² 

More than a decade ago, Mayo researchers studied the impact of a 7-valent pneumococcal conjugative vaccine (PCV7). That population-based study showed a reduction in disease caused by target serotypes but an increase in non-PCV7 serotypes.³

Tracking trends over a 16-year period

In the present study, the objective was to profile the incidence and clinical characteristics of IPD in Olmstead County, Minnesota, from January 1, 2002, to December 31, 2018, capturing periods of about 8 years before and 8 years after PCV13 was introduced.² (In 2014, the indication of prevention of IPD was expanded to all adults 鈮�65 years old.)

Based on 187 cases of IPD identified over the study period, the incidence fell from 11.1 cases to 5.6 cases per 100,000 person-years (P<.001) when the period of 2002 to 2010 was compared to the period of 2011 to 2018. Of these 187 cases, 112 (59.9%) patients had received at least 1 dose of the older or newer pneumococcal vaccine.

In the period after PCV13 was introduced, infection by the vaccine鈥檚 13 covered serotypes fell from 38.1% to 15.6% (P=.002). However, there was an increase in the incidence of non-PCV13 serotypes. Most notable after PCV13 became available, serotype 11A climbed from 1.0% to 6.2% of IPD cases, and serotype 33F increased from 2.9% to 15.6% of cases.

The overall reductions in IPD incidence following the availability of PCV13 were consistent across age groups, reaching about a 50% decline in children and adults. The exception was a substantially greater relative reduction in IPD incidence among those 51 to 64 years of age (15.9 cases per 100,000 person-years from 2002 to 2010, to 5.5 post-PCV13; P<.01). It鈥檚 unclear, however, why this age group had a greater relative benefit.

Even when vaccinated, older patients tend to do worse

Although survival was not assessed prior to and after the introduction of PCV13, 30-day survival rates were lower for those diagnosed after the age of 65 relative to younger patients (83.0% versus 94.6%). When compared to prior reports, 30-day mortality was lower, at 11.2%, than the 15% to 20% commonly reported in other population-based studies of IPD. However, variables other than vaccine, including socioeconomic status and access to medical care, might have contributed to the difference. 

The authors of this study, led by Supavit Chesdachai, MD, a clinical fellow in infectious disease at the Mayo Clinic, noted that studies conducted elsewhere, such as France, have shown cases of IPD following the introduction of PCV13 to increase after an initial decline, due to non-PCV13 serotypes. Similarly, an uptick in cases of non-PCV13 serotypes was observed in this study, although the increase was small. 

Overall, PCV13 has been associated with a decline in鈥攂ut not an elimination of鈥攖he risk of IPD, according to Dr. Chesdachai and his colleagues, who concluded that 鈥渢he complexities of the epidemiology of IPD dictate that ongoing surveillance is warranted.鈥�²

Published: January 30, 2023