The first COVID-19 vaccine candidate was administered during a clinical trial in March 2020, a triumph shared worldwide by all those working to overcome the deadly virus. A year later, there are almost 100 vaccines being tested in human trials, including new approaches to immunization whose development has been accelerated by the pandemic. Researchers are now working not just to prevent COVID-19 infections, but to prevent reinfection and address emerging variants as well.

Below, The Scientist rounds up those vaccine candidates that have advanced to clinical trials. 

See “Vector-Based Vaccines Come to the Fore in the COVID-19 Pandemic

See “The Promise of mRNA Vaccines

Editor’s note: The introduction of this story was updated on April 15, 2021.

Table updated July 9, 2021. New material highlighted in red.






Finlay Vaccine Institute/Pasteur...

In addition to vaccine candidates specific to SARS-CoV-2, several trials are underway testing vaccines against different pathogens as well as nonspecific formulations designed to stimulate an innate immune response.





Multiple organizations 


The Bacille Calmette-Guerin (BCG) vaccine for tuberculosis consists of live attenuated Mycobacterium bovis.

Lower rates of COVID-19–related deaths in countries with mandatory BCG vaccination prompted the launch of several clinical trials to test whether the immune response triggered by the vaccine may protect against SARS-CoV-2.

Several Phase 3 and 4 trials are underway.

Multiple organizations 


The measles-mumps-rubella (MMR) vaccine consists of live-attenuated strains of the three viruses.

Epidemiological data have revealed that places where the MMR vaccine is given as standard medical care have lower COVID-19 death rates than areas where MMR vaccination is not standard. Additionally, sailors aboard the U.S.S. Roosevelt who tested positive for COVID-19 had mostly mild symptoms, which some researchers suspect may have been due to administration of the MMR vaccine to all US Navy recruits.

A Phase 3 trial is underway in Egypt, led by researchers at Kasr El Aini Hospital. Separately, researchers at the Washington University School of Medicine are running an international Phase 3 trial of healthcare workers in the US, Canada, Europe, and Africa.

Immunovative Therapies, Mirror Biologics 


An off-the-shelf living immune cell

The affiliated companies are currently testing the formulation as a therapeutic vaccine for chemotherapy-refractory metastatic cancers.

A Phase 1/2 trial for healthy older adults has been approved to begin in New York.

Canadian Cancer Trials Group, others


Heat-killed Mycobacterium obuense

The vaccine is intended to stimulate nonspecific innate immunity. The company is also testing the vaccine in clinical trials for cancer.

A Phase 3 trial has been approved to begin in Canada.

Bandim Health Project


Oral polio vaccine, an attenuated strain of the poliovirus

Researchers argue that the vaccine is safer and available in greater quantities than the BCG vaccine against tuberculosis, which is also being tested as a possible COVID-19 preventive.

A Phase 4 trial has been approved to begin in Guinea-Bissau in West Africa.

Inmunotek, BioClever


A mixture of inactivated bacteria

The vaccine is intended to stimulate nonspecific innate immunity.

A Phase 3 trial for healthcare workers has been approved to begin in Mexico.



An inhaled combination of two synthetic Toll-like receptor agonists

The vaccine was originally developed as a potential therapeutic for cancer and has undergone early stage clinical testing. In mice, it provided protection against a range of respiratory pathogens, including MERS and SARS.

A Phase 2 trial for people with known SARS-CoV-2 exposure is underway in several US states.

Corrections: An earlier versions of this table stated that Janssen’s adenovirus-based COVID-19 vaccine candidate is administered intranasally. In fact, the vaccine is administered via intramuscular injection. / An earlier version of this table stated that the Phase 1 and Phase 2 Moderna trials were taking place in Seattle. In fact, there have been multiple locations since the Phase 1. / A previous update to this table implied that the adverse event that caused the Phase 3 AstraZeneca trial to be put on hold occurred in the Phase 1/2 trial in the UK. In fact, the event occurred in a participant enrolled in the Phase 3 UK study. / A previous update to this table listed Switzerland as having given emergency use approval for the Pfizer/BioNTech COVID-19 vaccine. In fact, the country granted its full approval. / A previous version of this table indicated that UAE and Bahrain had given emergency approval for the Beijing Institute of Biological Products’s COVID-19 vaccine; in fact, these countries have granted full approval. / A previous version of this table stated that Altimmunes vaccine was approved for a Phase 2 trial; in fact, it is approved for Phase 1. / A previous version of this table stated that China had approved the Sinopharm vaccine developed by Wuhan Institute of Biological Products in December 2020; in fact, that approval happened in February 2021. The Scientist regrets the errors.

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