Antibodies against MERS-CoV, including neutralizing antibodies, persisted in 6 (86%) of 7 persons 34 months after the 2012 MERS-CoV outbreak in Jordan. The observed persistence of these antibodies contributes to the understanding of individual immune responses to MERS-CoV infection, of population-based immunity in regions where MERS-CoV outbreaks have occurred, and to efforts for developing effective vaccines and therapeutics to counter MERS-CoV infections.
Notwithstanding improvements in public health awareness and infection control practices in affected countries on the Arabian Peninsula and in the Middle East, emergence of the virus (e.g., its introduction to South Korea and the resultant epidemic of 2015) ongoing. MERS-CoV continues to pose grave risks to international healthcare and socioeconomic systems.
It has been hypothesized that mild or asymptomatic MERS-CoV infections are potentially associated with lower levels of MERS-CoV neutralizing antibodies over time. All 7 case-patients reported here had respiratory symptoms, were relatively young, and had few underlying medical conditions (Table). Any association between our MERS-CoV antibody results and clinical severity is therefore difficult to assess. Nonetheless, of the 5 persons for whom chest radiographs showed substantial changes within 3 days of symptom onset, each remained positive by microneutralization (>20) 34 months after the outbreak.
Although some similarities in the short-term development of antibodies against MERS-CoV and SARS-CoV (e.g., seroconversion 2–3 weeks after illness onset) have been observed,[8,9] longer term serum antibody kinetics of these infections have not yet been compared. After SARS-CoV infection, robust IgG titers were observed through the second year but declined substantially during the third year after infection. Our finding of generally reduced but persistent MERS-CoV antibody responses even at 34 months suggests the potential for longer lasting antibody-mediated protective immunity against reinfection. However, whether such long-lasting antibodies can prevent reinfection or affect clinical outcome has yet to be examined. Diverse individual antibody test results allude to a potential role of genetic factors in explaining observed differences in immunologic responses to MERS-CoV exposure and infection.
The times at which MERS-CoV antibodies were measured in our study were chosen because of logistics and field practicalities. Although limited outbreaks of MERS-CoV have occurred in Jordan since 2012, contact tracing efforts by investigators in Jordan lead us to believe that these persons were not subsequently exposed. The observed ELISA titers and neutralizing antibody titers support this supposition; otherwise, we would expect increases resulting from a booster effect after secondary exposure and infection. To further assess the duration and resiliency of MERS-CoV antibodies in human populations, continued follow-up serologic evaluations of these persons would be desirable.
Emerging Infectious Diseases. 2016;22(10):1824-1826. © 2016 Centers for Disease Control and Prevention (CDC)