Although there have been several studies regarding the immunogenicity of one or two booster doses of the measles–mumps–rubella (MMR) vaccine in measles-seronegative young adults, limited data are available about how long the immune response is sustained compared with natural infection. This study included seronegative healthcare workers (HCWs) (aged 21–38 years) who received one or two doses of the measles–mumps–rubella (MMR) vaccine and HCWs with laboratory-confirmed measles infection during an outbreak in 2019. We compared neutralizing antibody titers measured using the plaque reduction neutralization (PRN) test and measles-specific immunoglobulin G (IgG) using chemiluminescent immunoassays 2 years after vaccination or infection. Among 107 HCWs with seronegative measles IgGs, the overall seroconversion rate of measles IgGs remained 82.2% (88/107), and 45.8% (49/107) of the participants had a medium (121–900) or high (>900) PRN titer after 2 years from one or two booster doses. The measles-neutralizing antibody titers of both PRN titer (ND50) and geometric mean concentration 2 years after natural infection were significantly higher than those of one or two booster doses of the MMR vaccine (p < 0.001 and p < 0.001, respectively). Our results suggest that serologic screening followed by appropriate postexposure prophylaxis can be beneficial for young HCWs without a history of natural infection especially in a measles outbreak setting, because of possible susceptibility to measles despite booster MMR vaccination 2 years ago. Long-term data about sustainable humoral immunity after one or two booster vaccination are needed based on the exact vaccination history.

Background:Recently published studies have found an impaired immune response after SARS-CoV-2 vaccination in solid organ recipients. However, most of these studies have not assessed immune cellular responses in solid organ transplant recipients. In this study, a prospective double-arm cohort study was performed to evaluate the humoral and cellular immune response to SARS-CoV-2 vaccination in solid organ transplant recipients compared to healthy staff members with the normal function of the immune system. Methods: A total of 64 transplant patients and an age-matched control group of 103 healthy staff members were included. Blood samples were obtained and analyzed after the second dose and the boosting (third) dose, respectively. For evaluation of the virus-neutralization capacity of each group, serum was analyzed using a surrogate SARS-CoV-2 neutralization test to quantify the functional inhibitory capacity of neutralizing antibodies (Genscript) against SARS-CoV-2 spike protein. Inhibition scores of under 30% were considered negative. Results: Except for the vaccination subgroup of initial two dosages of AstraZeneca followed by Pfizer was significantly higher in the healthy control group, other prime-booster combination subgroup proportion was similar between the group. After the standard two doses of vaccination, only 28.3% of the transplant recipients demonstrated positive functional inhibition of neutralizing antibodies, significantly lower than 70.9% of the healthy control group (P<0.001). Even after the booster (third) dose of vaccination, 43.2% of the transplant recipients showed positive functional inhibition of neutralizing antibodies, significantly lower than 100% of the healthy control group (P<0.001). No other immune-associated complications such as acute rejection occurred after SARS-CoV-2 vaccination in the transplant recipient group. Conclusions: Our data strongly suggest revised vaccination approaches in immunocompromised patients, including individual immune monitoring for the protection of this vulnerable group at risk of developing severe COVID-19. It urges a review of future vaccine strategies for these patients.