TIMING OF VACCINATION GOES NOT AFFECT ANTIBODY-RESPONSE OR SURVIVAL AFTER PNEUMOCOCCAL CHALLENGE IN SPLENECTOMIZED RATS

Background: Pneumococcal vaccination after splenectomy for trauma decr eases the incidence of overwhelming postsplenectomy infection. The opt imal timing of vaccination has not been established. This study was co nducted to determine whether timing of vaccination after splenectomy a ffects antibody response or survival after pneumococcal challenge. Met hods: Sprague-Dawley rats were used for all experiments. Control rats (n = 30) were divided into three equal groups and underwent splenectom y followed by sham vaccination 1, 7, or 42 days after splenectomy. Tre ated rats (n = 66) were divided into three equal groups and underwent splenectomy followed by vaccination with polyvalent pneumococcal vacci ne 1, 7, or 42 days after splenectomy. All rats then underwent intrape ritoneal Streptococcus pneumoniae inoculation with the predetermined l ethal dose for 50% of the population 10 days after vaccination. Rats w ere observed for a 72-hour period after inoculation, and mortality was recorded. Immunoglobulin G and immunoglobulin M antibody titers were determined before vaccination and before inoculation to determine anti body response. Results: Mortality was greater in the control group tha n in the treatment group (21 of 30 [70%] vs. 2 of 64 [3%];p < 0.01), T here were no differences in mortality within either the control group (1 day, 6 of 10; 7 days, 7 of 10; 42 days, 8 of 10; p = 0.62) or the t reatment group (1 day, 0 of 21; 7 days, 0 of 21; 42 days, 2 of 22; p = 0.14), immunoglobulin G and immunoglobulin M antibody responses were greater in vaccinated than in nonvaccinated rats. There was no effect of timing of vaccination on antibody response. Conclusion: Pneumococca l vaccine reduces mortality from postsplenectomy infection. Timing of vaccination after splenectomy does not affect survival from a pneumoco ccal challenge or antibody response in rats. This study supports the p ractice of administering vaccine within 24 hours of splenectomy when v accine cannot be administered before surgery.