Just consider the South African variant of the coronavirus, somewhat inelegantly dubbed 501Y.V2 for now. This strain of the coronavirus (and there are plenty of coronavirus strains beyond the ones which cause COVID) appears to be far more contagious and transmissible than the Chinese and European strains that were prevalent in the early days of the pandemic.

The reason? The mutations in the South African strain affect the “spike protein,” the essential tool that the novel coronavirus uses to infiltrate the body’s cells. And those mutations appear to make it easier to spread, though it’s unclear if it actually makes the virus deadlier. There haven’t been any reported cases of this variant in the U.S. to date. But that could easily change with more time and robust surveillance, and the South African strain has spread to at least 20 other countries according to the World Health Organization (WHO), including the U.K., France, Switzerland, Japan, Austria, and Zambia.

As scary as a coronavirus mutation may sound, it’s par for the course with any transmissible virus. Take the flu for example. Per the Centers for Disease Control (CDC), there are four separate strains of the flu virus, and those strains can have their own subtypes. It’s sort of like how the same language may be spoken with different dialects.

But that biological diversity necessitates a diversity of vaccines. The flu isn’t just one consistent vaccine from year to year (although some biopharmaceutical companies are attempting to create a universal influenza shot). Viruses adapt and change just as any other biological entity does. That’s why public health official have to keep such a close eye on the contours of a mutation in order to facilitate more effective products that build on the existing ones.

Such mutations have practical implications and raise concerns over whether or not currently available vaccines would be as effective against them. Transmissibility worries led Moderna, which makes one of the two COVID vaccines currently authorized in the U.S., to announce Monday that it is working on a booster shot to deal with the South African variant.

“Out of an abundance of caution and leveraging the flexibility of our mRNA platform, we are advancing an emerging variant booster candidate against the variant first identified in the Republic of South Africa into the clinic to determine if it will be more effective to boost titers against this and potentially future variants,” said Moderna CEO Stephane Bancel in a statement.

As with everything COVID-related, it’s too early to say definitively how effective the current vaccines would be against a mutated coronavirus. Moderna believes its vaccine would provide at least some protection even against this particular South African COVID strain, as well as a different coronavirus mutation first identified in the U.K.

The WHO has been cautious in its messaging about vaccine efficacy against new strands. “In terms of natural immunity or immune-derived therapeutics, mutations in the spike protein of the B.1.351 or 501Y.V2 may, in theory, reduce, but not obliterate the recognition of the virus by antibodies. This is because, in practice, the human immune system will recognize more than a single region of the spike protein,” writes the agency. “Mutations may reduce vaccine efficacy directed against the spike protein but will not obliterate their effects.”

Vaccine makers have long known this reality. A flu vaccine may be 60% effective against one particular strain but just 30% effective against another. Moderna’s vaccine is about 95% effective for the original coronavirus strain and medical leaders hope that it will still be at least 70% effective against new variants such as the South African and U.K. strains.

What’s concerning is that the vaccine doesn’t seem to produce quite as robust of an immune response, which is critical to warding off the virus. A an efficacy rate around 70% is still far better than nothing—after all, that’s why public health officials insist everybody get a flu shot even if it’s not very effective in a given year—but also explains why Moderna is preparing its booster shot.

How fatal these coronavirus offspring could be is another question. Prime Minister Boris Johnson initially said there was “some evidence” that the U.K. variant made the virus more deadly, but public health and government officials have tempered those claims since, cautioning that there’s still a great deal of uncertainty about the strain’s deadliness.

Moderna’s move is precautionary and it’s far too early to tell if these new variants are significantly more deadly than the previous ones. So far, that doesn’t seem to be the case. And the company believes the malleability of its mRNA-based vaccine, which can be manufactured and scaled up faster than other types of vaccines due to its underlying technology, gives Moderna the flexibility to prepare for a more dangerous COVID variant.

If nothing else, the pandemic has underscored the important of preparation when it comes to potential infectious disease threats in the future.