Monkeying Around with a COVID-19 Vaccine

Image credit: “Gibraltar Barbary Macaque” by Redcoat is licensed under the Creative Commons Attribution-Share Alike 2.5 Generic license.

This post was reviewed by Dr. Emily Bowman, one of our subject matter experts.

This study was conducted by researchers from Beijing Bio-Institute Biological Products Co Ltd, China CDC, Peking Union Medical College, National Institute for Food and Drug Control, and Tsinghua University.

The paper we’ll be demystifying can be found here, if you’d like to follow along!

TL;DR: Researchers from Beijing created an inactivated vaccine, named BBIBP-CorV, against SARS-CoV-2 by altering an existing clinical isolate (HB02). Tests in monkeys showed its ability to protect against infection while displaying few side effects. A multiple dosage program appears to yield the best results.

A SARS-CoV-2 vaccine: the holy grail of 2020/2021. Although there are many treatments and precautions that we can take against SARS-CoV-2, a vaccine could take off a lot of the pressure. It’s a mad dash for researchers to develop a working vaccine, with over 140 potential candidates on the World Health Organization’s (WHO) radar.  

Today’s candidate is brought to you by an intrepid team of researchers from Beijing and their simian friends. Because of our similarities with various other primates, testing their potential vaccine on monkeys helped these researchers bridge the gap between lab rats and potential patients. Their goal was to create an inactivated vaccine, a version of the virus altered to be non-infectious, but similar enough for the immune system to use it to recognize and attack the real deal. Our talented author, Deanna, has written a more detailed explanation of vaccines here!

The first step in making the vaccine was getting the raw materials: the virus itself. Researchers collected three isolates of SARS-CoV-2 from three COVID-19 patients. The three clinical isolates, 19nCoV-CDC-Tan-HB02 (HB02), 19nCoV-CDC-Tan-Strain03 (CQ01), and 19nCoV-CDC-TanStrain04 (QD01), were different enough to cover the majority of SARS-CoV-2 varieties.

The researchers infected Vero cells, a cell line from the African green monkey, with these viruses. They used the cells to assess the proliferation and genetic stability of the isolates. Good proliferation is vital for large scale vaccine manufacturing, and genetic stability means that a virus is less likely to mutate. Out of the three isolates tested, HB02 displayed the greatest proliferation in Vero cells, so it was selected for additional testing, and was further shown to have high genetic stability. After growing out the HB02, the researchers inactivated it with β-propionolactone, a sweet-smelling liquid used to inactivate viruses for vaccines. This candidate vaccine was called BBIBP-CorV.

Their first vaccine test was for immunogenicity, that is, the ability of BBIBP-CorV to produce an adequate immune response in an animal model. It was given to mice in high (8 mg/dose), middle (4 mg/dose), and low (2 mg/dose) doses. By 7 days, all mice produced antibodies against HB02 through a process called seroconversion, and these antibody levels continued to increase over time. Without vaccination, you’re seronegative. Through seroconversion, your body will produce neutralizing antibodies (NAbs) in response to the vaccine. In this case, these NAbs can theoretically bind to HB02, preventing it from infecting other cells. When the seroconversion rate hits 100%, you become seropositive and may gain protection against a virus.

To assess how different dosing strategies affect the immunogenicity of BBIBP-CorV in mice, the researchers set about experimenting with a second vaccine dose 7, 14, or 21 days after the initial immunization. These “double-dose” mice had a much greater immune response than those only vaccinated once. Of these vaccination programs, administering the second dose 21 days after the first dose yielded the greatest amount of NAbs. Likewise, when they tried a three-dose program, with one dose per week, they observed an even higher level of NAbs.

Researchers then tested BBIBP-CorV in other animal models: rabbits, rats, guinea pigs, actual pigs, and the titular monkeys. In all animals tested, single doses of BBIBP-CorV resulted in a 100% seroconversion rate by day 21, and the triple-dose program further increased the levels of NAbs present in the blood.

Knowing the rhesus macaques react similarly to SARS-CoV-2 infection in humans, the team used them to test the protective ability of their vaccine, vaccinating them twice, two weeks apart. The monkeys were either injected with a placebo dose of saline, a low dose of BBIBP-CorV (2 mg/dose), or a high dose of BBIBP-CorV (8 mg/dose). Ten days after the second dose, the macaques were infected with SARS-CoV-2.

Our simian science soldier, the rhesus macaque.
Image credit: “Rhesus Macaque monkey look” by Md. Tareq Aziz Touhid is licensed under the Creative Commons Attribution-Share Alike 4.0 International license.

For the next week, all the macaques’ temperatures stayed within normal range and their blood chemistry remained constant. To see if it worked, researchers took swabs and analyzed them with real-time PCR, a lab technique that measures the amount of SARS-CoV-2’s genetic material present in a sample.

The placebo macaques had a high viral load, essentially large amounts of SARS-CoV-2 present in the body. Those given the low dose of BBIBP-CorV had far lower viral loads by one week, with three out of four having an undetectable viral load. All macaques given the high dose had clean throat swabs, being negative for viral loads, along with half of the high-dose macaques having clean anal swabs.

Inspecting the lungs directly, researchers could not detect viral loads in any lobe of the BBIBP-CorV-vaccinated monkeys. The placebo macaques, however, had high viral loads in the left lower lung, right lower lung, and right accessory lung. Similarly, while the BBIBP-CorV-treated macaques only had mild adverse changes to the lungs on the cellular level, the placebo monkey displayed severe pneumonia. As such, both dosages of BBIBP-CorV provided protection against SARS-CoV-2.

The final test was essential: safety. The researchers first injected 10 rats with a triple-dose of BBIBP-CorV and another 10 with a saline control. There were no clinical signs of adverse reactions after 14 days of observation, nor were there any signification changes in weight or feeding between the two groups. Tissue studies didn’t display any changes on the cellular level, also known as the histopathology. By pushing to find the upper dosing limit, researching found that the maximum tolerated dose (MTD) in the rats was 24 mg/dose, or 900x the human equivalent, although this estimate is very preliminary.

Next, the team checked for a potential anaphylactic allergic reaction, using guinea pigs as a model. They were divided into four groups of nine guinea pigs and dosed twice, a week apart. The negative control group was given saline and had no allergic reaction. The positive control group was given human blood albumin and had severe anaphylactic reactions. The other two groups were given either high or low doses of BBIBP-CorV and displayed no allergic reaction.

Finally, the researchers checked for long-term toxicity of BBIBP-CorV with 40 cynomolgus monkeys. They were observed for 36 days, being injected weekly for the first three weeks (four injections total). There were no significant clinical and anatomical changes, and levels of immune cells and proteins remained within a normal range. Some inflammation was noticed by day 25, although it decreased by day 36. The local irritation at the injection site resolved after 2 weeks.

While this all sounds quite promising, these results are very preliminary, and it’s essential to remember that the vaccine development timeline is a long, careful process. There are various steps built into the development process to ensure the safety and efficacy of potential vaccines like BBIBP-CorV. Without these steps, we risk circulating a non-functional vaccine, or worse, damaging our own health.

For now, practicing social distancing and wearing masks when necessary is vital. No monkey business!

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