Vaccine Covid19

Covid-19: two candidate vaccines induce an immune response

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The scientific journal The Lancet reveals in its pages that two vaccines in the trial phase, one in the United Kingdom and the other in China, elicited an immune response in the volunteers who received them.

This week, the prestigious scientific journal The Lancet published the preliminary results of two candidate vaccines, one developed by a British team and the other by a Chinese team. Both visibly induced an immune response in the vaccinated volunteers.

In both studies, the researchers used a weakened adenovirus, the common cold virus, which was genetically engineered to carry the genetic code for the proteins found on the outside of SARS-CoV-2. The immune system in contact with this modified virus is supposed to produce antibodies intended to defend itself against this pathogen, and the body will be ready to fight the disease when it comes back in contact with these viral proteins. In theory, therefore, the vaccine should not cause disease, but should be effective enough for the body to develop sufficiently to defend itself.

How many people have received the candidate vaccine?

For the Oxford study, the cold virus came from chimpanzees and was administered to 543 of the approximately 1,077 healthy adults who participated, while the remaining 534 were a control group and received a meningitis vaccine. So far, the results have shown that the vaccine candidate induces a strong immune response in antibodies and T lymphocytes (cells of the immune system) until day 56 of the current trial. And those responses could be even higher after a second dose, according to an ongoing study in a subgroup of 10 participants.

For the Chinese study, 508 people participated in a phase II clinical trial. This phase consists of a preliminary evaluation of the efficacy of the candidate vaccine at the selected dose. Of the participants, 253 received a high dose of the vaccine, 129 received a low dose, and 126 received a placebo. Verdict: 95% of participants in the high-dose group and 91% in the low-dose group exhibited T-cell or antibody immune responses on day 28 after vaccination. The patients were not followed for more than 28 days, so long-term immunity has not been studied.

Is the observed immune response sufficient?

"The immune system has two ways to find and attack pathogens: antibodies and T-cell responses. This vaccine is intended to induce both, so that it can attack the virus as it circulates in the body," as well as cells. infected. We hope this means that the immune system will remember the virus, so that our vaccine will protect for an extended period, "said Professor Andrew Pollard of Oxford University, lead author of the study." However, we need more research before be able to confirm that the vaccine effectively protects against SARS-CoV-2 infection and for how long that protection lasts, "he added.

Admitting that "much work remains to be done before we can confirm whether this vaccine will help manage the Covid-19 pandemic," Professor Sarah Gilbert, co-author of the study, believes "these initial results are promising."

"In addition to continuing to test our vaccine in phase 3 trials, we need to learn more about the virus, for example, we still don't know how much an immune response needs to obtain effective protection against infection by SARS-CoV-2," he added. . The authors of the UK study said recruited participants will be followed for at least a year to continue studying the vaccine's safety and the immune response it elicits.

The caveat is the same on the Chinese study side: "An additional dose may be necessary to induce a stronger immune response in the elderly population, but additional research is underway to evaluate it," Professor Wei Chen said. , from the Beijing Biotechnology Institute, co-author of the Chinese study. Compared to the younger population, older participants in this study generally had significantly lower immune responses and greater tolerance to the vaccine than younger participants. However, the trial only followed the participants for 28 days, and no data on the durability of immunity induced by this vaccine is yet available.

What adverse effects for these two vaccines against Covid-19?

For the Oxford study, minor side effects such as fatigue, headache, pain at the injection site, and muscle pain were reported by approximately 70% of the participants. They were less intense in the participants who were askedhe erred on taking paracetamol, which did not adversely affect the immune response.

In addition, in the 10 people who received the extra dose of the vaccine, side effects were less frequent after the second dose.

In the Chinese study, the same adverse effects (fever, muscle pain, chills, etc.) were reported, with maximum low to moderate intensity. At 28 days, only 9% of participants in the high-dose group had serious side effects, including high fever. And the proportion was much lower (1%) among the participants who received the lowest dose.

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