At the beginning of the COVID-19 pandemic, convalescent plasma was one of very few interventions available. Now that scientists have learned more about the Sars-Cov-2 virus and the disease it causes, they are developing new ways to cope with the effects of COVID-19.
More potential treatments are in development, and researchers are taking a closer look at convalescent plasma to determine whether it is an effective treatment option and how to use it in the fight against COVID-19.
Plasma is the liquid part of the blood, made of about 92 percent water plus coagulants, proteins, electrolytes, and immunoglobulins or antibodies.
Convalescent plasma for COVID-19 is plasma taken from people who have recovered from COVID. What makes this liquid special is that it contains antibodies that can combat the virus. When someone with an active Sars-Cov-9 infection receives convalescent plasma, the hope is that the newly introduced antibodies will help them combat the infection.
Convalescent plasma is not new. Scientists and healthcare providers have used it in the past to treat Spanish flu, bird flu, and ebola. They believe it is most effective when given early to people exposed to a new virus, but there is some question about whether it also could benefit people experiencing advanced disease with complications like organ damage or inflammation.
Some studies found that the length of hospital stay was the same between people with COVID who received convalescent plasma and those that did not. Two large studies show that it does not improve mortality in COVID-19, while many smaller studies show that it does.
Evidence on the effectiveness of convalescent plasma for COVID-19 is difficult to interpret, and more research is needed for a clear answer.
One theory about why convalescent plasma appears to have varying effectiveness is high and low-titers. People who recover from COVID-19 do not all have the same level of antibodies: some have more and some have less.
Plasma with a lot of antibodies has a high-titer. Some studies show that using high-titer convalescent plasma leads to better outcomes than low-titer.
The severity of the recipient's COVID-19 infection also seems to determine whether convalescent plasma is an effective treatment. One study involved adult outpatients who came to the emergency room with mild symptoms of COVID-19 during the first week of their infection. All participants had at least one known risk factor for severe COVID-19. Half of them received convalescent plasma and half placebo. The study results show no difference in disease progression between the two groups.
Whether convalescent plasma helps hospitalized patients improve is also difficult to determine. Some studies show no evidence that the treatment benefits patients more than standard hospital care when considering mortality. Those who received convalescent plasma and had shorter symptoms ultimately had the same outcomes as those who did not receive the treatment. These studies included people with generally healthy immune systems.
It is worth noting that studies suggest convalescent plasma appears to benefit immunosuppressed people hospitalized with COVID-19.
The timing of convalescent plasma treatment seems to play a role in its effectiveness. One study found that patients who received convalescent plasma with a high titer within 44 hours of hospital admission had the biggest improvement in mortality rates.
This same study also shows that patients who needed a ventilator when arriving at the hospital and those who received high titer convalescent plasma more than 72 hours after admission saw no mortality benefit.
Researchers did most of their convalescent plasma studies on Sars-Cov-2 variants before Omicron became dominant, and research suggests it is less effective against this new variant. One study on patients infected with the Omicron variant shows that convalescent plasma is half as effective against Omicron as it is against the Beta variant.
Monoclonal antibodies are another treatment developed for COVID-19, and while they share some characteristics with convalescent plasma, there are some stark differences, too.
Monoclonal antibodies use the same principle as convalescent plasma, as they both rely on antibodies to fight the virus. The difference is convalescent plasma comes from the blood of COVID survivors, and monoclonal antibodies come from a lab. The big advantage of monoclonal antibodies is that the number of antibodies is standardized, which can make results more reliable. With convalescent plasma, the number of antibodies depends on the donor.
More research into convalescent plasma and COVID-19 is needed. Researchers suggest studies should look more closely at the duration of symptom onset before treatment, which patients convalescent plasma would benefit most, and the effects on the types and proportion of circulating variants.
Larger studies on the overall effectiveness of convalescent plasma would also be beneficial.
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