This is part of our <\/em>Coronavirus Update<\/em><\/a> series in which Harvard specialists in epidemiology, infectious disease, economics, politics, and other disciplines offer insights into what the latest developments in the COVID-19 outbreak may bring.<\/em><\/p>\n

With nearly 5 million confirmed cases globally and more than 300,000 deaths from COVID-19, much remains unknown about SARS-CoV-2, the virus that causes the disease. Two critical questions are whether vaccines will prevent infection with COVID-19, and whether individuals who have recovered from COVID-19 are protected against re-exposure to the virus.<\/p>\n

Now, a pair of new studies led by researchers at Harvard-affiliated Beth Israel Deaconess Medical Center (BIDMC) suggests the answer to these questions is yes, at least in animal models. Results of these studies were published today in the journal Science.<\/p>\n

\u201cThe 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,\u201d said senior author Dan H. Barouch, director of the Center for Virology and Vaccine Research at BIDMC. \u201cIn 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.\u201d<\/p>\n

In the first study, the team found that six candidate DNA vaccines \u2014 each formulation using a different variant of the key viral protein \u2014 induced neutralizing antibody responses and protected against SARS-CoV-2 in rhesus macaques.<\/p>\n

Barouch and colleagues, who began working toward a COVID-19 vaccine in mid-January when Chinese scientists released the SARS-CoV-2 genome, developed a series of candidate DNA vaccines expressing variants of the spike protein, the part used by the virus to invade human cells and a key target for protective antibodies. The vaccines are designed to train the body\u2019s immune system to recognize the virus swiftly upon exposure and respond quickly to disable it.<\/p>\n

To assess the efficacy of the vaccines, the researchers immunized 25 adult rhesus macaques with the investigational vaccines. Ten animals received a sham version as a control group. Vaccinated animals developed neutralizing antibodies against the virus. Three weeks after a booster vaccination, all 35 animals were exposed to the virus. Follow-up testing revealed dramatically lower viral loads in vaccinated animals, compared with the control group. Eight of the 25 vaccinated animals demonstrated no detectable virus at any point following exposure to the virus, while the other animals showed low levels of virus. Moreover, animals that had higher antibody levels had lower levels of the virus, a finding that suggests neutralizing antibodies may be a reliable marker of protection and may prove useful as a benchmark in clinical testing of SARS-CoV-2 vaccines.<\/p>\n