The earlier plasma is collected after the donor’s recovery from Covid-19 the better, as antibodies start to disappear after three months of symptom onset, researchers have said.
Although trials are still ongoing to analyse the clinical benefits and role of convalescent plasma to treat coronavirus, a new study suggests it may be more effective the earlier it is collected.
When someone is infected with a virus, their body makes antibodies to fight the infection.
After recovery, antibodies may remain in a person’s blood plasma for months or even years.
Convalescent plasma treatment involves people who are newly ill – in this case with Covid-19 – receiving plasma from a person who has recovered.
It is hoped that receiving the plasma will help bolster their own ability to fight off the virus and limit its severity.
Study author Renee Bazin, of the Hema-Quebec blood centre in Canada, said: “While many clinical trials are under way to better understand whether convalescent plasma is clinically beneficial for treating Covid-19, a key question is at what time point is it most effective to collect donor plasma based on the presence of antibodies that help fight the virus.
“Based on our findings, antibodies against the new coronavirus are not eternal.”
The small study, published in the journal Blood, drew from 282 Covid-19 plasma donors in Quebec, Canada.
It followed 15 adults – 11 males and four females – who were diagnosed with and subsequently recovered from Covid-19.
Although symptoms ranged from mild to severe, none of the donors were hospitalised for treatment.
The participants each donated their plasma between four and nine times, with the first donation occurring between 33 and 77 days after symptom onset, and the last donation between 66 and 114 days.
Dr Bazin found that people who produced antibodies against the virus later became seronegative, which means there were no detectable antibodies after a certain point.
The research suggests the decline in antibodies over time appears unrelated to the number of times a person donates blood plasma.
Instead, it is thought it is due to the elapsed time since the infection and a natural waning of the immune response.
All 15 donors showed decreases in antibodies at the same time, around 88 days, and half of the detectable antibodies decreased within 21 days afterwards, the study found.
Dr Bazin said: “The antibodies disappear rapidly, so people recovering from Covid-19 who want to donate blood plasma should not wait too long once they become eligible to donate.”
She added: “Based on our findings, clinicians should ideally use plasma that is collected early on after a donor’s onset of symptoms and check for the presence of antibodies before giving donor plasma to a patient.”
Dr Bazin noted that almost 7% of the original 282 donors did not have detectable antibodies at their first donation and this proportion doubled when considering donors who waited more than 11 to 12 weeks after symptom onset before donating.
She said that if antibodies wane three to four months after a peak of infection, the prevalence of the infection in communities or populations could be underestimated.
Researchers plan to follow plasma blood donors over time, and future studies will try to determine if certain plasma is more beneficial.
Separate research in the UK is assessing whether convalescent plasma donations can be transfused into patients who are struggling to develop their own immune response.
NHS officials are collecting plasma for a major trial in the UK.