Pneumococcal Vaccine Reduced Nonsusceptibility in Adults

Introducing a vaccine against Streptococcus pneumoniae (S. pneumoniae or Sp) in the U.S. led to significant reductions in nonsusceptibility to multiple antimicrobial agents among pneumococcal isolates among adults, according to a paper published in Journal of Infection.

Investigators from Pfizer collected 7254 S. pneumoniae isolates from adults with suspected pneumonia in 105 hospital settings between 2009 and 2017 in order to assess S. pneumoniae nonsusceptibility in this group. Susceptibility was measured using guidelines from the Clinical and Laboratory Standards Institute.

The investigators tested 7 antimicrobial agents: penicillin G (PEN), ceftriaxone (CEF), clindamycin (CLIN), erythromycin (ERYTH), tetracycline (TETRA), levofloxacin (LEVO), and vancomycin (VAN). They also defined multidrug resistance as intermediate or resistance to 3 or more of these 7 agents.

Since 2010, the 13-valent pneumococcal conjugate vaccine has been recommended for children; it was recommended for adults under the age of 65 beginning in 2014, the study authors said. Despite widespread vaccination, 4 million pneumococcal disease cases remain annually in the U.S. as well as 22,000 related deaths, they added.

Two-thirds of the samples were from patients aged 18-64 years while the remaining samples were from those aged over 65 years, the study authors said. The majority of isolates were from noninvasive sources (84%), but the study authors added that 15% and 1% were from invasive and unknown sources, respectively. The most common isolate sources were sputum (50%), bronchoalveolar lavage (BAL) fluid (15%), blood culture (12%) and tracheal aspirate (8%), they said.

Over the course of the collection period, the percentage of all pneumococcal isolates due to the vaccine decreased from 39% to 22%, the study authors determined.

Antimicrobial nonsusceptibility peaked for PEN and CEF in 2009 and for TETRA, CLIN, and multidrug resistance in 2011, the study authors found. Following 2011, nonsusceptibility for PEN and CEF decreased from nearly 14% to 4% and 11% to 3%, respectively, with a plateau after 2015, the investigators said.

CLIN nonsusceptibility decreased from 22% in 2011 to 13% in 2015, but increased to 17% in 2017, the study authors learned. Additionally, the percentage of multidrug resistant isolates decreased from 16% in 2011 to 13% in 2015 and increased again to 16% in 2017. ERYTH nonsusceptibility was stable, the study authors said, and low for LEVO during the study periods. All of the isolates were susceptible to VAN, the study authors added.

“The observed reductions in Sp antimicrobial nonsusceptibility were mainly driven by the decreased prevalence of PCV13-type isolates from 2009 to 2017, with serotype 19A initially accounting for 17.4% of the isolates in 2009 but only 3.9% of the isolates in 2017,” corresponding study author Jose A. Suaya, MD, MPH, PhD, told Contagion® in an email. “Nonsusceptibility patterns across antibiotics were serotype-specific and may be explained by multiple mechanisms.”

Antimicrobial nonsusceptibility proportions were similar between invasive and noninvasive isolates throughout the study period, the authors said, and there were comparable proportions for PEN and CEF between groups.

Suaya said that antibiotic resistance is a critical threat to public health, but existing and developing vaccines may be one way to combat the threat. The study authors added that millions of annual deaths and trillions of dollars could be the consequence by 2050 if this threat goes unaddressed.

“Our study adds evidence that the use of a vaccine in a population, in this case PCV13, by preventing vaccine-type disease and avoidance of antibiotic use, among other factors, appears to be an additional tool to combat antimicrobial resistance,” Suaya concluded. “Adherence to vaccination schedules, as recommended by ACIP, can be emphasized.”