Despite there having been more than 1,100 known survivors of MERS-CoV infection (mostly in Saudi Arabia), we've seen very little in the way of post-convalescent follow up on these cases.
Aside from obvious concerns over post-MERS Sequelae, another area of interest is the level, and persistence, of MERS antibodies among the survivors. While viral infections usually leave behind some degree of immunity in the recovered host, their effectiveness and longevity can vary widely
And among camels, at least (see MERS Coronavirus in Dromedary Camel Herd, Saudi Arabia and EID Journal: Replication & Shedding Of MERS-CoV In Inoculated Camels) - we've seen some limited evidence of repeat infections.
Today the EID Journal looks at 9 Health care workers who were infected during the 2014 Jeddah outbreak (2 severe pneumonia, 3 milder pneumonia, 1 URTI, and 3 asymptomatic), and finds that only those with severe pneumonia still carried detectable levels of antibodies 18 months later.
Those who experienced a milder pneumonia had shorter lived antibody responses (1 out to 10 months, 2 out to 3 months), while the URTI and asymptomatic cases tested negative at 3 months post infection.
While a small study, if the results hold true on a larger scale this raises some interesting questions, including:
- Are those who only experienced mild or moderate illness at risk of re-infection?
- Would convalescent plasma donated by those without severe illness be ineffective?
- Does this skew (under count) the community seroprevalence studies we've seen coming out of Saudi Arabia and Kenya?
- How will all of this play into the development of a MERS-CoV vaccine (for camels or humans)?
Volume 22, Number 6—June 2016
Antibody Response and Disease Severity in Healthcare Worker MERS Survivors
Abeer N. Alshukairi , Imran Khalid, Waleed A. Ahmed, Ashraf M. Dada, Daniyah T. Bayumi, Laut S. Malic, Sahar Althawadi, Kim Ignacio, Hanadi S. Alsalmi, Hail Al-Abdely, Ghassan Y. Wali, Ismael A. Qushmaq, Basem M. Alraddadi, and Stanley Perlman
A study evaluating the immune response in patients infected with severe acute respiratory syndrome coronavirus (SARS-CoV) showed antivirus antibodies in survivors can be detected by ELISA and immunofluorescence assay (IFA) for up to 24 months after infection (1). Another study revealed that SARS-CoV antibodies were not detectable at 6 years after infection (2). Antibody response to Middle East respiratory syndrome coronavirus (MERS-CoV) typically is detected in the second and third week after the onset of the infection (3–5), but little is known about the longevity of the response or whether the decrease in antibody response over time correlates with the severity of the initial infection. We conducted a longitudinal study of antibody response among a cohort of MERS survivors who had been treated at King Faisal Specialist Hospital and Research Center in Jeddah, Saudi Arabia (KFSHRC-J).
We studied antibody response in 9 healthcare workers in Jeddah, Saudi Arabia, who survived Middle East respiratory syndrome, by using serial ELISA and indirect immunofluorescence assay testing. Among patients who had experienced severe pneumonia, antibody was detected for >18 months after infection. Antibody longevity was more variable in patients who had experienced milder disease.
The 2 patients with severe pneumonia had the highest antibody titers detected among all patients and remained MERS-CoV-antibody–positive when tested at 18 months after illness onset. They also had prolonged viral shedding documented by persistent positive rRT-PCR results for 13 days (patient 1) and 12 days (patient 2); rRT-PCR analyses were negative after 2–5 days for patients 4–9. rRT-PCR was only repeated at day 13 for patient 3, and the result was negative.
Three patients with pneumonia were MERS-CoV-antibody–positive at 3 months, but antibody was detected in only 1 of the 3 at 10 months (Table). All patients who had an upper respiratory tract function or remained asymptomatic had no detectable antibody response on the basis of ELISA and IFA results.
In conclusion, our results indicate that MERS-CoV antibody persistence depends on disease severity. Further studies are required to determine the role of the virus-specific T-cell response in MERS patients and determine whether patients with mild infections are at risk for reinfection and would therefore benefit from vaccination. Our data also show that potential donors of MERS-CoV convalescent-phase serum samples are limited to patients who recover from severe pneumonia.
Dr. Alshukairi is an infectious diseases consultant at KFSHRC-J. Her interests include tuberculosis and infections in immunocompromised hosts.
We thank Mohamma Rasmi Gabajah for help in obtaining blood samples from HCWs.
This work was supported by the Pathology Department at KFSHRC-J. S.P. was supported by a grant from the US National Institutes of Health (grant no. PO1 AI060699).