- An experimental coronavirus vaccine developed by China's CanSino Biologics triggered immune system responses in healthy adults enrolled into a clinical trial conducted in Wuhan, China, the initial epicenter of the COVID-19 pandemic.
- Study results, published Friday in The Lancet, suggest the vaccine could be helping train the body to recognize and resist infection by the new coronavirus, and show inoculation at lower doses appeared generally safe.
- Researchers emphasized, however, that not enough is known about immune responses to coronavirus infections to determine with any certainty whether the vaccine would actually be protective. Additionally, about half of the people tested had pre-existing immunity to the inactivated virus CanSino uses for its vaccine, compromising some of the responses
Eight vaccines for SARS-CoV-2 are now in initial human testing, the product of an unprecedented push by scientists, governments and companies the world over to compress a normally years-long process into just months.
Much of the early attention has fallen on Moderna, the frontrunner in the U.S., which this week sparked a stock market rally with a limited glimpse at preliminary results from a Phase 1 study of its vaccine candidate.
The first person treated in that trial, which is being run by the National Institute of Allergy and Infectious Diseases, was vaccinated on March 16, around the same time that Chinese researchers nearly 6,000 miles away inoculated for the first a healthy adult in Wuhan with CanSino's shot.
Over the next 11 days, a total of 108 healthy adults were enrolled into CanSino's trial and selected to receive either a low, medium or high dose of the vaccine.
Researchers, working as the city around them was under strict lock down, were thorough. Adults in the study were put up in a designated hotel for 14 days post-vaccination, and measured for immune responses at two and four weeks.
Results showed nearly all participants developed binding antibodies — the immune system's frontline defenders — by day 28. Laboratory testing showed 63, including 27 of the 36 given a high vaccine dose, developed so-called neutralizing antibodies, capable of destroying live SARS-CoV-2 virus in a test tube. Immunization also resulted in T-cell responses, hinting at broader immune involvement.
While the data suggest the vaccine is working as intended, researchers cautioned that it's not yet known what levels of antibodies are required to confer protection against infection by SARS-CoV-2.
"Therefore, we are unable to predict the protection of the ... COVID-19 vaccine on the basis of the vaccine-elicited immune responses in this study," the researchers wrote.
Umer Raffat, a biotech analysts at Evercore ISI, called the findings "underwhelming" in a note to clients, while acknowledging the uncertainty around what would be needed for immunity.
Vaccination didn't result in any side effects classified as "serious" after 28 days. The most common problems reported were fever, fatigue, headache and muscle pain.
In five participants given the high dose, however, researchers noted episodes of Grade 3 fever, which played a role in their decision to take forward into Phase 2 testing only the low and medium doses. Two participants on each of those doses experienced Grade 3 fever.
Although Moderna publicly disclosed initial results earlier this week, CanSino can now claim the academic distinction of having the first clinical trial results of a coronavirus vaccine published in a peer-reviewed medical journal.
Much more information, therefore, is now available on CanSino's candidate, which uses an inactivated adenovirus to deliver DNA into human cells. Those genetic instructions tell the cell to produce a key protein found on the surface of SARS-CoV-2, in theory training the body's immune system to recognize and neutralize the virus when an infection occurs.
Moderna's vaccine, by contrast, skips DNA entirely and shuttles into cells messenger RNA encoding for the same coronavirus protein.
Both technologies, while enabling of faster design and development, are newer approaches to vaccination, and therefore aren't as proven as traditional protein-based or recombinant vaccines.
The Lancet data suggest that pre-existing immunity to the adenovirus used by CanSino could be interfering with the desired immune responses to vaccination. Fifty-five participants had high pre-existing immunity to CanSino's chosen adenovirus upon enrolling in the study and, in those people, analysis showed that familiarity to the virus partially compromised the development of neutralizing antibodies.
Researchers also noted that older age "could have a negative effect on the vaccine-elicited responses to SARS-CoV-2." If borne out, that could pose a major hurdle to use of CanSino's vaccine among the older populations who are most at risk of severe COVID-19. The engineered antibodies many other drugmakers are developing for the disease, by comparison, likely wouldn't have those issues, though the protection they'd offer is temporary.
The now-enrolling Phase 2 study will include participants older than age 60, researchers said.
In addition to that trial in China, CanSino recently secured a go-ahead from Canadian health authorities to begin study of the vaccine there, as China's outbreak has now waned. CanSino is partnered with the Beijing Institute of Biotechnology on vaccine development.
Moderna, as well as others, are also moving quickly to advance their candidates into larger trials. The Cambridge, Massachusetts-based biotech has clearance from the Food and Drug Administration to move into Phase 2 testing and aims to begin a Phase 3 study this summer.
The University of Oxford also announced on Friday the start of a 10,000-person Phase 2 trial of a DNA-based vaccine that it's licensed to AstraZeneca.