These are the top coronavirus vaccines to watch

The first vaccine to be cleared by U.S. regulators was developed by pharmaceutical giant Pfizer and its German partner BioNTech. BioNTech began working on a vaccine in January last year, and the companies began working together in March, broadening a joint effort to use the same technology to develop an influenza vaccine. In November, companies reported that the vaccine was more than 90 percent effective in late-stage trials and were granted emergency use authorization on Dec. 11. The second vaccine, developed by Moderna in partnership with the National Institute of Allergy and Infectious Diseases, got the greenlight from the FDA days later.

These steps are now overlapping in the race to find vaccines for a global disease that has killed hundreds of thousands of people. Human testing began in some cases before animal studies were finished. As companies launched small Phase 1 trials intended to establish the correct dose, they were already planning the Phase 3 trials to evaluate whether the vaccines were effective and safe.

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No steps are being skipped, top government officials have repeatedly promised, and vaccines will not be considered for approval in the United States until after a large, Phase 3 trial. The Food and Drug Administration, which has the ultimate say on whether a vaccine has been proved safe and effective, says any vaccine for covid-19, the disease caused by the coronavirus, will need to prevent disease or decrease symptoms in at least 50 percent of those who receive it. The effectiveness of the flu vaccine ranges from 40 to 60 percent, according to the Centers for Disease Control and Prevention.

Unprecedented speed

Researchers in the United States set an audacious goal in January last year to develop a coronavirus vaccine within 12 to 18 months. The vaccine created by Pfizer and BioNTech is the fastest ever developed and authorized in the United States.

Historically, vaccines have taken years to develop. Before these, the mumps vaccine — which took four years to develop — was the fastest to be approved for use in humans, in four years, from scientific concept to approval in 1967.

Developing messenger RNA vaccines such as the Pfizer-BioNTech and Moderna candidates has been fast because scientists were able to start their work before there was a known case of the novel coronavirus in this country, using the viral genome shared online as a template. Making messenger RNA vaccines does not require time-consuming steps, such as growing ingredients in chicken eggs.

Pfizer invested $2 billion of its own money into the vaccine and then struck a $1.95 billion contract with the U.S. government to provide 100 million doses, contingent on the vaccine being effective. Moderna developed its vaccine in partnership with the National Institute of Allergy and Infectious Diseases, with the government underwriting the research and development of the vaccine and the advanced purchase of 200 million doses, bringing the government investment to $4.1 billion.

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New technologies

Advancements in science and technology have given researchers new tools to try against the coronavirus. Scientists can deliver genetic material into the body’s cells, turning them into vaccine factories and skipping time-consuming steps such as manufacturing viral proteins or growing the whole virus in chicken eggs.

The Pfizer and the Moderna vaccines are the first vaccines using messenger RNA technology ever cleared for human use outside of clinical trials. It is different from more traditional vaccines, which often use a weakened or dead version of a virus, or a laboratory-generated protein.

The core of the coronavirus SARS-CoV-2 is a single strip of ribonucleic acid (RNA) surrounded by a protein shell. The virus is named for the iconic spikes that project from its center like a crown, or “corona” in Latin. These spike proteins aren’t just decoration. They are critical for the virus to get inside cells and make copies of itself.

Vaccines work by teaching the body’s immune system to recognize and block viruses. Each category of vaccine technology works under this basic principle. Vaccines aim to activate the immune system’s T-helper cells, which are responsible for detecting the presence of a virus. They instruct B-cells to create antibodies that block the virus from being able to replicate and T-killer cells to destroy infected cells. Some vaccines may activate only part of this immune response.

Here is a look at how different vaccine technologies being developed around the world would ideally elicit an immune response to prevent SARS-CoV-2 in humans. Each vaccine may vary somewhat in how it works, but each would generally follow these steps.

Vaccines using nucleic acid (DNA and RNA)

DNA vaccines contain genetic material that carries the blueprint for the spike protein. To get the DNA into cells, researchers use an electrical pulse to disrupt the cell membrane. Once inside, the DNA is used as a template to create spike protein.

RNA vaccines contain a strip of genetic material within a fat bubble. Once inside the cell, the RNA generates a protein found on the surface of the virus. The immune system, presented with the protein, learns to recognize the virus.

These vaccines have the advantage of speed — they can be quickly designed and manufactured. But they have never been approved for use outside of medical research and will likely require two doses.

Viral-vectored vaccines

Some vaccines use a virus that has been engineered to be harmless to ferry a gene from the coronavirus into cells. The gene codes for a distinctive part of the coronavirus, and the immune system learns to recognize it.

Viral-vectored vaccines can be designed quickly. One concern is that people can develop immunity to the viral vector, making this approach potentially less useful if booster shots need to be given.

Subunit vaccines

Some traditional vaccines work by delivering viral proteins to cells. The technologies to manufacture those protein fragments vary, but companies are using insect cells and yeast. The hepatitis B vaccine relies on a viral protein created by genetically engineered yeast.

Weakened or inactivated virus vaccines

In a more old-fashioned approach, the virus is weakened so that it does not cause disease, but still triggers the immune system’s defenses. The vaccine for measles, mumps and rubella uses this approach.

Inactivated virus vaccines contain dead virus, incapable of infecting people but still able to instruct the immune system how to mount a defensive reaction against an infection. The polio vaccine invented by Jonas Salk used this approach, and flu vaccines use this technology.

These vaccines typically take longer to manufacture.

Other vaccines

Information on the technology platform being used was not available for all the experimental vaccines. Some vaccines being tested do not specifically target the coronavirus, but aim to increase the body’s first line of immune defenses.