Authors: Katherine Gordon, Future Science Group
As scientists around the world continue to work towards developing a successful vaccine candidate for COVID-19, many questions surrounding the virus and its treatment remain unanswered, including whether a vaccine could prevent infection, and whether previous infection does prevent re-exposure. In an attempt to investigate these questions, researchers at the Beth Israel Deaconess Medical Center (MA, USA) have conducted two studies, recently published in Science, testing their candidates in rhesus macaques.
“The global COVID-19 pandemic has made the development of a vaccine a top biomedical priority, but very little is currently known about protective immunity to the SARS-CoV-2 virus,” explained senior author Dan Barouch. “In these two studies, we demonstrate in rhesus macaques that prototype vaccines protected against SARS-CoV-2 infection and that SARS-CoV-2 infection protected against re-exposure.”
In the first of the two studies, the team injected 25 adult rhesus macaques with one of six candidate DNA COVID-19 vaccines while a further ten received a sham control. Immediately after immunization, the vaccinated macaques began to develop neutralizing antibodies against the virus.
Then, 3 weeks after providing them with a boost vaccination, the researchers exposed all 35 macaques to the COVID-19 virus. Of the 25 vaccinated animals, eight demonstrated no detectable virus at any point following exposure, and in all of the others the level of the virus was significantly lower than that of the control group.
The researchers also observed an association between antibody levels and viral loads, with the macaques who developed the highest number of neutralizing antibodies against the virus after vaccination also displaying the lowest levels of viral loads after exposure.
In the second study, again using macaques, the researchers aimed to investigate whether those who contract and recover from COVID-19 are protected from reinfection. To this end, they exposed nine adult rhesus macaques to the virus and monitored their viral levels as they recovered.
All of the animals infected survived and recovered, having produced antibodies against the virus. Upon re-exposure to the virus a month later, all macaques demonstrated nearly complete protection.
“Our findings increase optimism that the development of COVID-19 vaccines will be possible,” remarked Barouch. “Further research will be needed to address the important questions about the length of protection, as well as the optimal vaccine platforms for a SARS-CoV-2 vaccines for humans.”
Sources: Yu J, Tostanoski LH, Peter L et al. DNA vaccine protection against SARS-CoV-2 in rhesus macaques. Science doi:10.1126/science.abc6284 (2020); Chandrashekar A, Liu J, Martinot AJ et al. SARS-CoV-2 infection protects against rechallenge in rhesus macaques. Science doi:10.1126/science.abc4776 (2020); https://news.harvard.edu/gazette/story/2020/05/vaccines-found-that-may-protect-against-covid-19-in-animal-models/