Covid-19 vaccines are the start of a new wave of genetic medicine—drugs that tweak DNA to keep us healthy.

Both the Pfizer and Moderna Covid-19 vaccines use messenger RNA (mRNA) to instruct our cells to make a new protein—in this case, the spike protein on the SARS-CoV-2 virus—so our immune systems respond to it like a threat.

But there are other ways to use or alter genetic material to improve a patient’s health. Scientists can:

• Extract certain cells, modify them with gene editing enzymes like Crispr, and then reintroduce them to our bodies
• Insert a new gene to make up for a faulty one using a benign, modified virus to sneak into our cells (these are called gene therapies, and they were some of the earliest iterations of genetic medicine)

Each of these methods presents its own challenges. Here are a few:

• Crispr could cause an immune reaction, which could potentially cause more damage
• Some scientists and patients balk at the idea of permanently changing our genetic master code in select cells. Even if it works, it’s a cumbersome process, and if a mistake happens, it’d be permanent for the cell’s lifetime (although notable, these therapies could never jump to non-targeted cells)
• There are problems with delivery. Getting the treatment to the right cells is difficult. We need a much larger amount of genetic material to tell our cells to make a certain protein than existing small molecule drugs. The mRNA has to be encapsulated in something (usually lipid nanoparticles) so it’s not attacked by the body, are hard to engineer.

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