Weekly newsletter:
May 17-23 2021
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Passive immunotherapy may be ineffective
Some patients infected with SARS-CoV-2 require hospitalisation, since the . illness may get worse to the point of causing severe respiratory failure. In patients with severe forms of COVID-19, immunomodulatory drugs such as corticosteroids may help reduce the number of deaths. However, antiviral medicines such as Remdesivir do not reduce mortality, but only the number of hospitalisations. Humoral immunity (antibodies) plays an essential role in the immune response to SARS-CoV-2, but this response becomes strong only several weeks after infection. In patients with severe forms of COVID-19, stronger antibody responses have been observed, but they occur with significant delay.
Observations of this nature have previously been used to develop treatment using plasma (which contains antibodies) from individuals who have recovered from infections. It is called passive immunotherapy and has been used for more than a hundred years. A study by the RECOVERY Collaborative Group (Oxford University) has recently published results on the effectiveness and safety of this treatment using plasma from patients recovered from COVID-19 on individuals hospitalised with the same illness.
11 558 patients enrolled for this study, half of them having received plasma from recovered individuals, and the other half having been treated according to more conventional procedures. 92% of the patients had already received conventional treatment by corticosteroids before the two groups were formed. The average age was 63,5 and the average time since the first appearance of symptoms was 9 days. 5% needed to be put on ventilators, 87% received oxygen and 8% had no need of help with breathing.
The first conclusion to be drawn was that there is no difference in mortality rates after 28 days between patients treated by immunotherapy and those receiving conventional treatment: 24% of patients in each group died. There was also no significant difference where ventilators were used. In addition, the causes of death were similar with or without the use of immunotherapy. And, with or without immunotherapy, the duration of symptoms or the time before the patient’s eventual death was the same, no matter what the age or ethnic origin of the individual.
The researchers did attempt to explain immunotherapy’s apparent lack of success. The method had been successful against other illnesses such as viral pneumonia. Why were results not the same with COVID-19?
This may depend on the levels of neutralising antibodies contained in the plasma used, since their levels were not measured (only the anti-spike antibodies were measured). However, the majority of patients in the study received two doses of plasma taken from two different patients, which increases the chances of receiving one with high levels of neutralising antibodies.
Another hypothesis was that the treatment may only be effective if administered at an early stage of the illness. However, no improvement in the state of patients having received the treatment earlier (less than 4 days after the appearance of symptoms) was observed. No differences in effectiveness were noted either before or after the emergence of the UK variant in England.
Treatment by passive immunotherapy using the plasma of patients having recovered from SARS-CoV-2 infection did appear to be promising in the combat against COVID-19, especially since it was readily available. However, it seems to be ineffective, both in respect of patients’ survival or the duration or seriousness of their symptoms.
