Last April, in EID Journal: Antibody Response & Disease Severity In HCW MERS Survivors, we looked at a study that tested 9 Health care workers who were infected during the 2014 Jeddah outbreak (2 severe pneumonia, 3 milder pneumonia, 1 URTI, and 3 asymptomatic), that found 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 admittedly a very small sample, at the time I posed the following questions:
- 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)?
Today we've a new study published in the EID Journal that appears to confirm the short-lived antibody response among convalescent MERS cases across a much larger sampling, and which leaves the questions posed above still very much in play.
First the link and abstract, then I'll be back with more.
Volume 22, Number 9—September 2016(continue . . . )
Feasibility of Using Convalescent Plasma Immunotherapy for MERS-CoV Infection, Saudi Arabia
Yaseen Arabi Comments to Author , Ali H. Hajeer, Thomas Luke, Kanakatte Raviprakash, Hanan Balkhy, Sameera Johani, Abdulaziz Al-Dawood, Saad Al-Qahtani, Awad Al-Omari, Fahad Al-Hameed, Frederick G. Hayden1, Robert Fowler, Abderrezak Bouchama, Nahoko Shindo, Khalid Al-Khairy, Gail Carson, Yusri Taha, Musharaf Sadat, and Mashail Alahmadi
We explored the feasibility of collecting convalescent plasma for passive immunotherapy of Middle East respiratory syndrome coronavirus (MERS-CoV) infection by using ELISA to screen serum samples from 443 potential plasma donors: 196 patients with suspected or laboratory-confirmed MERS-CoV infection, 230 healthcare workers, and 17 household contacts exposed to MERS-CoV. ELISA-reactive samples were further tested by indirect fluorescent antibody and microneutralization assays.
Of the 443 tested samples, 12 (2.7%) had a reactive ELISA result, and 9 of the 12 had reactive indirect fluorescent antibody and microneutralization assay titers. Undertaking clinical trials of convalescent plasma for passive immunotherapy of MERS-CoV infection may be feasible, but such trials would be challenging because of the small pool of potential donors with sufficiently high antibody titers.
Alternative strategies to identify convalescent plasma donors with adequate antibody titers should be explored, including the sampling of serum from patients with more severe disease and sampling at earlier points during illness.
The full report is very much worth reading, as the implications of their findings could prove substantial. In their discussion section, the authors address three of these:
- `Our findings suggest that the low prevalence of seroreactivity for MERS-CoV, even among persons with confirmed or suspected infection, may be a reflection of a short-lasting antibody response.'
- `A short-lasting immune response may also partly explain why negligible or low levels of MERS-CoV seroreactivity have been detected in persons at risk for the disease (i.e., camel and abattoir workers) in Saudi Arabia and elsewhere (23–26).'
- `Our findings also raise questions about whether naturally occurring infections and potential MERS-CoV vaccines will offer long-lasting immunity.'
The prospects for a human MERS-CoV vaccine anytime soon have always been slim, given it is now 13 years since SARS emerged, and no viable vaccine has been produced.
A camel targeted vaccine makes more sense for a lot of reasons.
But with no proven therapeutics available, the obstacles in obtaining large quantities of convalescent plasma can only be viewed as a major disappointment.