The only thing better than a new study that showed positive results for the COVID-19 vaccine in monkeys were two studies. Newspapers, published back-to-back Science this week are some of the first to show that nonhuman primates can develop protective immunity against SARS-CoV-2 – an important finding for vaccines and public health strategies.
“The global COVID-19 pandemic has made vaccine development a top biomedical priority, but currently very little is known about immunity to the SARS-CoV-2 virus,” said senior author Dan H. Barouch, MD, PhD, professor of medicine, Harvard Medical School, director, Center for Virology and Vaccine Research, BIDMC, and senior authors on both studies. “In these two studies, we showed rhesus monkeys that the prototype vaccine was protected from SARS-CoV-2 infection and that SARS-CoV-2 infection was protected from repeated exposure.”
Earlier this year, a study investigating cynomolgus macaques found these animals to be promising models for testing COVID-19 therapy. To investigate whether infection with SARS-CoV-2 results in immune protection against re-exposure, the researchers developed a SARS-CoV-2 infection ape model that recapitulates certain aspects of human infection SARS-CoV-2. In the newspaper, “SARS-CoV-2 infection protects against rechallenge in rhesus macaques“They tested whether the nine adult animals that had cleared the virus were immune to the challenges of the virus 35 days later.
After exposing nine adult apes to the SARS-CoV-2 virus, the researchers monitored the level of the virus when the animals recovered. The nine animals recovered and developed antibodies against the virus. More than a month after the initial infection, the team again exposed rhesus macaques to the virus. After the second exposure, the animal showed almost complete protection against the virus. This data shows the natural protective immunity against COVID-19 in this model.
The authors write that “apes have high viral loads in the upper and lower respiratory tract, humoral and cellular immune responses, and pathological evidence of viral pneumonia.” After clearing the initial virus, they explained, animals were challenged again with SARS-CoV-2 and “showed 5 logs10 reduction in mean viral load in bronchoalveolar lavage and nasal mucosa compared with primary infection. “
The nine animals showed little or no symptoms after repeated challenges and showed an immune response that protects against a second infection (given at the same dose as the first).
Additional research will be needed to determine the natural immune endurance shown here, the authors note. “Rigorous clinical studies will be needed to determine whether SARS-CoV-2 infection effectively protects against repeated exposure of SARS-CoV-2 in humans,” they said.
In a separate study that included many of the same researchers, entitled “Protection of DNA vaccines against SARS-CoV-2 in rhesus macaques, “The team developed a series of DNA vaccine candidates that expressed various forms of the SARS-CoV-2 Spike (S) protein and evaluated it in 35 rhesus macaques (25 adult rhesus macaques with the vaccine under study and 10 animals received false controls).
Vaccinated animals develop humoral and cellular immune responses, including neutralizing antibody titers comparable to those found in humans and recovered apes infected with SARS-CoV-2.
Importantly, when these vaccinated macaques were intranasally infected with SARS-CoV-2 six weeks later, they showed sufficient levels of antibodies in their blood to neutralize the virus within two weeks. Follow-up tests showed a dramatically lower viral load in vaccinated animals compared to the control group. Eight of the 25 vaccinated animals showed that no viruses were detected at any point after exposure to the virus, and other animals showed low levels of the virus.
In addition, higher levels of antibodies are associated with lower viral loads, suggesting that antidote antibodies can function as protective correlations and may prove useful as benchmarks in clinical testing of the SARS-CoV-2 vaccine.
“Our findings increase optimism that the development of the COVID-19 vaccine will be possible,” Barouch said. “Further research is needed to answer important questions about the duration of protection, as well as the optimal vaccine platform for SARS-CoV-2 vaccine for humans.
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