CanSino coronavirus vaccine appears safe in first human trial

In recent studies rhesus macaque monkeys were infected with the coronavirus and developed symptoms but created protective antibodies and recovered after a few days thanks to a prototype vaccine. — AFP pic

But in one study, monkeys developed immunity against the new SARS-CoV-2 coronavirus after receiving experimental vaccines.

At least 100 vaccines against COVID-19 are now in development, with at least eight starting clinical trials, the authors noted, among them Moderna's mRNA vaccine, and the University of Oxford's non-replicating chimpanzee adenovirus-vectored vaccine, which was recently shown to be protective in a small preclinical trial.

"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.

Further research is needed to find out how long this natural immunity lasts, the study authors noted.

An adenovirus type-5 (Ad5) vectored vaccine against the COVID-19 coronavirus was well-tolerated and provoked immune responses in healthy volunteers, Chinese researchers reported.

A Reuters poll published Thursday found that a quarter of Americans were not very or not at all interested in getting a vaccine for the virus that has infected more than 1.6 million people in the US.

Three weeks vaccination, all 35 animals were exposed to the virus. All nine also had few or no symptoms after re-exposure and had immune responses that appeared to protect them against a second infection. The latest development in their study is that monkeys which were infected with the virus developed an immunity when they were re-infected with the virus after recovering.

After two weeks, the vaccine produced virus-fighting antibodies across all dose levels, with the highest dose level triggering antibodies in 61 percent of those who took it.

More than 100 vaccine candidates against SARS-CoV-2 are in development, with about 12 in human testing created to mainly evaluate safety.

The authors wrote that "macaques had high viral loads in the upper and lower respiratory tract, humoral and cellular immune responses, and pathologic evidence of viral pneumonia". Follow-up testing revealed dramatically lower viral loads in vaccinated animals compared to the control group.

"But we also show that the levels of antibodies correlate with how good the protection is".

A second study involved 25 monkeys, all of which were tested using six prototype vaccines to see if antibodies produced in response were protective.

"Rigorous clinical studies will be required to determine whether SARS-CoV-2 infection effectively protects against SARS-CoV-2 re-exposure in humans", they said. The problem was more common among subjects at the older end of the age range, among 45 to 60 year olds - a finding that raises questions about how well the vaccine would work in one of the demographic groups that most needs protection from this infection, older adults.

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