Coronavirus: Chinese vaccine 'safe', triggers immune response

Henrietta Strickland
May 24, 2020

For example, vaccines must be examined for causing an effect known as antibody-dependent enhancement (ADE), whereby vaccine-induced antibodies that bind to the virus also attach to the body's cells, facilitating infection of these cells - a concerning phenomenon that has been observed in vaccines against dengue, Ebola, HIV, and feline coronavirus.

"The global COVID-19 pandemic has made the development of a vaccine a top biomedical priority, but very little is now known about protective immunity to the SARS-CoV-2 virus", said Dan H. Barouch, MD, PhD, professor of medicine, Harvard Medical School, director, Center for Virology and Vaccine Research, BIDMC, and senior author on both studies.

"These results represent an important milestone", the lead researcher on the study, Professor Wei Chen, said. However this is not the final trials and the overall results would be evaluated in six months.

A possible vaccine against SARS-COV-2, the strain of coronavirus that causes COVID-19, has been shown to be at least partially effective, a Chinese study published Friday confirmed. However, the researchers cautioned that the results should be interpreted carefully. "The challenges in the development of a COVD-19 vaccine are unprecedented, and the ability to trigger these immune responses does not necessarily indicate that the vaccine will protect humans from COVID-19".

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Because age has been identified as a risk factor for severe COVID-19, the authors said they included participants older than age 60 in a phase II trial now underway. These then recognise the spike protein and fight off the coronavirus, the researchers explained.

108 healthy adults aged between 18 and 60 years were sequentially enrolled in the study. The volunteers were divided into three groups of 36 and the vaccine was given intramuscularly with a single shot in increasing doses to the three groups - low dose (5 x 1010 viral particles per 0.5 mL vial), middle dose (1 x 1011viral particles per 1 mL vial) and high dose (1 x 1011 viral particles per 1.5 mL vial). These are the body's humoral response', which is the part of the immune system that produces antibodies to fight infection, and the "cell-mediated' arm, which depends on a group of T cells to fight the virus, the scientists said". "We selected doses for the phase-2 study mainly on the basis of the safety profile of the candidate vaccines shown in the participants within seven days and 14 days post-vaccination", they note. Instead, it's vital to take time to ensure any vaccine candidate's safety and investigate potential adverse effects, he says. The antibody response to the vaccine in the high-dose group was slightly greater than that in the middle-dose and low-dose groups. The most common adverse reactions were fever, fatigue, headache and muscle pain. The vaccine elicited a four-fold increase in binding antibodies to the spike protein's receptor-binding domain in 94%-100% of participants and a four-fold increase in antibodies to live virus in 50%-75%. On further analyses, the researchers said the majority of recipients showed either a positive T cell response, or had detectable neutralising antibodies against SARS-CoV-2 as much as 28 days after vaccination.

The study also showed that the antibody and immune response could be reduced by high pre-existing immunity to the adenovirus - a common cold virus.

"Our study found that pre-existing Ad5 immunity could slow down the rapid immune responses to SARS-CoV-2 and also lower the peaking level of the responses".

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