It has been touted as a breakthrough treatment by Donald Trump, and there are hopes that blood plasma containing coronavirus antibodies may help British patients during the second wave of Covid-19 as well.
But a study, which is published in the British Medical Journal (BMJ) on Friday, suggests “convalescent plasma” has only limited effectiveness and fails to reduce deaths or stop the progression to severe disease.
Plasma is the clear, yellowish liquid part of the blood which carries red and white blood cells and platelets around the body. After an infection, plasma is often packed with antibodies generated by the immune system. As such, it is sometimes harvested from people who have recovered from a disease and transfused into patients who are fighting it. This convalescent plasma therapy was used during the 1918 flu pandemic, as well as during more recent global health emergencies, treating patients with Sars or Ebola.
Various trials around the world are exploring whether convalescent plasma could help reduce deaths and serious complications from Covid-19, with the largest randomised controlled trial taking place in the UK.
Despite the findings of the latest published study, convalescent plasma may yet prove to be effective against Covid-19.
The research involved 464 adults with moderate Covid-19 who were admitted to hospitals in India between April and July. Approximately half received two transfusions of convalescent plasma, 24 hours apart, alongside standard care, while the control group received standard care only.
One month later, 19% of those who received the plasma had progressed to severe disease or had died of any cause, compared with 18% in the control group. Plasma therapy did, however, seem to reduce symptoms, such as shortness of breath and fatigue, after seven days.
A spokesperson for NHS Blood and Transplant, which is collecting plasma from people who have recovered from Covid-19, emphasised that UK-based studies are only infusing plasma that contains high levels of coronavirus antibodies. He said the Indian study used plasma with antibody levels around six to 10 times lower than that.
The Indian researchers agreed that further studies using high antibody levels may find it to 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.
Followup data from all 351 patients in the Texas study has been published as a preprint and supports this conclusion, although plasma transfusion later in the course of the disease had no significant effect on death rates regardless of antibody levels. “With respect to altering mortality, our analysis identified an optimal window of 44 hours post-hospitalisation for transfusing Covid-19 patients with high titre convalescent plasma,” they wrote.
Prof Paul Morgan, the director of the Systems Immunity Research Institute at Cardiff University and a member of the British Society for Immunology’s expert taskforce on immunology and Covid-19, said there were other reasons for optimism. For one thing, he said, the study suggested plasma therapy was associated with a reduction in viral load, “so, there does seem to be an antiviral effect of the therapy, even if it isn’t reflected in the final outcomes”.
The study also hinted that infusing patients with large amounts of donated plasma could lead to a small but significant increase in deaths. “It might be worth considering, rather than giving just convalescent plasma, taking the antibodies out of the plasma and using those,” Morgan said. Such purified antibodies are already used to treat patients with antibody deficiencies.