Almost all recommended vaccines in the U.S. can be safely administered concomitantly at different anatomic sites to immunocompetent adults, without compromising immunogenicity or safety.
 
Exceptions include the 13-valent pneumococcal conjugate vaccine (PCV13) and the 23-valent pneumococcal polysaccharide vaccine (PPSV23), which can elicit lower antibody responses if received together, according to a new report in Open Forum Infectious Diseases. In addition, a study of the live zoster vaccine (ZVL), which is no longer used in the U.S., found that concomitant administration with PPSV23 resulted in a lower varicella zoster virus antibody response than receipt of the vaccines more than 4 weeks apart.

Kaiser Permanente Southern California researchers and colleagues point out that no real-world observational study identified a difference in the risk of HZ between individuals who received PPSV23 and ZVL concomitantly and those who received the vaccines at least 4 weeks apart. The Advisory Committee on Immunization Practices continued to recommend concomitant vaccination of ZVL with other vaccines for eligible recipients.

Further, they wrote, "In randomized, controlled trials, coadministration of RZV with other vaccines (i.e., tetanus, diphtheria, and acellular pertussis vaccine [Tdap], quadrivalent inactivated influenza vaccine [IIV4], and PPSV23) did not interfere with humoral immune responses, and no safety concerns were identified."

They added, however, "Because the relationship between humoral immune responses and HZ risk is unclear, and HZ risk following concomitant vaccination with RZV has not been evaluated, we conducted a large retrospective cohort study at Kaiser Permanente Southern California (KPSC) to directly evaluate HZ risk among individuals who received RZV with and without concomitant vaccination."

The two-dose RZV series is recommended for the prevention of HZ in adults aged 50 years or older, and the cohort study included Kaiser Permanente Southern California members in that group who received two doses of RZV 4 weeks to 6 months (or fewer) apart from April 1, 2018, to September 30, 2019.

RZV recipients with and without same-day concomitant vaccination for either of the RZV doses were followed up for incident HZ beginning 31 days after the second RZV dose until September 30, 2020.

The study involved 12,898 people who received RZV with concomitant vaccination and 28,353 who received only the one vaccine. Results indicated that HZ occurred among 41 individuals with concomitant vaccination (incidence rate, 2.2 [95% CI, 1.6-3.0] per 1,000 person-years) and 136 without concomitant vaccination (3.4 [95% CI, 2.9-4.0] per 1,000 person-years). The authors calculated the adjusted HR for HZ comparing RZV recipients with and without concomitant vaccination as 0.75 (95% CI, .53-1.08).

"HZ risk was not significantly different between RZV recipients with and without concomitant vaccination, supporting recommendations allowing for concomitant administration of RZV with other vaccines," the researchers concluded.

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