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Donald Trump has touted it as a groundbreaking treatment, and there is hope that blood plasma containing antibodies to the coronavirus could also help British patients during the second wave of Covid-19.
But a study, published in the British Medical Journal (BMJ) on Friday, suggests that “convalescent plasma” has limited efficacy and fails to reduce deaths or stop the progression to serious disease.
Plasma is the clear, yellowish liquid part of the blood that carries red and white blood cells and platelets throughout the body. After an infection, plasma is often packed with antibodies generated by the immune system. As such, it is sometimes obtained from people who have recovered from a disease and is transfused into patients who are fighting it. This convalescent plasma therapy was used during the 1918 flu pandemic, as well as during the most recent global health emergencies, to treat patients with Sars or Ebola.
Several trials around the world are exploring whether convalescent plasma could help reduce deaths and serious complications from Covid-19, and the largest randomized controlled trial is taking place in the UK.
Despite the findings of the latest published study, convalescent plasma may still be effective against Covid-19.
The investigation involved 464 adults with moderate Covid-19 who were admitted to hospitals in India between April and July. About half received two convalescent plasma transfusions, 24 hours apart, along with standard care, while the control group received only standard care.
One month later, 19% of those who received the plasma had progressed to severe disease or died from any cause, compared with 18% in the control group. However, plasma therapy appeared to reduce symptoms, such as shortness of breath and fatigue, after seven days.
A spokesperson for the NHS Blood and Transplant, which collects plasma from people who have recovered from Covid-19, emphasized that studies conducted in the UK are only infusing plasma that contains high levels of antibodies to the coronavirus. He said the Indian study used plasma with antibody levels six to ten times lower than that.
The Indian researchers agreed that further studies using high levels of antibodies may be more effective. An interim analysis of 136 Covid-19 patients in a trial at Houston Methodist Hospital in Texas suggested a significant reduction in deaths among patients who received plasma with high levels of antibodies early in the course of their disease.
Follow-up data for the 351 patients in the Texas study have been published as preprint and support this conclusion, although plasma transfusion later in the course of the disease had no significant effect on death rates regardless of blood levels. antibodies. “With regard to altered mortality, our analysis identified an optimal window of 44 hours after hospitalization for the transfusion of Covid-19 patients with high-titer convalescent plasma,” they wrote.
Professor Paul Morgan, director of the Systems Immunity Research Institute at Cardiff University and a member of the British Society for Immunology expert working group on immunology and Covid-19, said there were other reasons for optimism. For one thing, he said, the study suggested that plasma therapy was associated with a reduction in viral load, “so there appears to be an antiviral effect of the therapy, even if it is not reflected in the final results.”
The study also hinted that the infusion of large amounts of donated plasma to patients could lead to a small but significant increase in deaths. “It might be worth considering, rather than just giving convalescent plasma, get the antibodies out of the plasma and use them,” Morgan said. These purified antibodies are already used to treat patients with antibody deficiencies.
