Many Americans have abandoned their facemasks. They’re going to see friends and family. They’re going out to eat once more. For the most part, life has returned to normal.

Unfortunately, the situation is very different in other parts of the world. The main distinction is the availability of vaccines. In the United States, 88 COVID-19 vaccine doses were given to every 100 people. Only 15 doses per 100 people are administered in India.

The US government secured major supply agreements with leading vaccine manufacturers, including Moderna (NASDAQ: MRNA) and Pfizer (NYSE: PFE). These companies made billions of dollars, but thanks to their vaccines, the United States appears to have turned the corner in the fight against COVID-19. Things, however, may be about to change. Moderna’s ominous warning could cause havoc in the COVID-19 vaccine market.

Moderna held its fourth annual Science Day last week. The company laid out its research and development plans in this virtual event for investors. However, top biotech scientists issued an alert reminiscent of Paul Revere’s famous call that the British were on their way. In this case, Moderna’s warning was that new COVID-19 waves were on their way.

“As the virus spreads, it is rapidly mutating,” said Moderna’s chief scientific officer Melissa Moore. “Some of these new viral strains appear to be even more transmissible than the original strain,” she added.

The good news is that vaccines developed by Moderna and Pfizer, in particular, have proven to be highly effective thus far. The bad news, as Moore puts it, is that “some of these new strains are already less susceptible to neutralization by our current vaccine.” Lower neutralizing antibody levels against several key coronavirus variants have been found to be concerning by Moderna’s researchers, implying a risk of reduced duration of protection against infection. Moderna believes that “new epidemic waves are undoubtedly on the way” because some of these variants are more transmissible.

What does this all imply for Americans and the COVID-19 vaccine market? In the end, booster shots and new vaccines targeting the variants are likely to be required.

Dr. Anthony Fauci, President Biden’s chief medical advisor and former director of the National Institute of Allergy and Infectious Diseases, believes we won’t know for sure if booster doses are required until the fall. According to Moderna’s findings, it’s not a matter of if, but of when, booster shots will be required.

The emergence of potent new variants has the potential to change the dynamics of the COVID-19 vaccine market. Companies that have concentrated their efforts solely on developing vaccines targeting the original coronavirus strain risk falling behind if they do not quickly shift their focus to developing variant-specific vaccines. Vaccine manufacturers face two primary challenges. To begin, the rapid mutation of coronaviruses necessitates a technological approach that allows for the rapid development of variant-specific vaccine candidates. Second, companies will require financial resources not only to develop new vaccines, but also to conduct clinical trials.

Smaller biotechs that do not have large cash stockpiles or supply agreements in place for their COVID-19 vaccines may be at a significant disadvantage in the fast-moving market. Larger pharmaceutical companies that have had setbacks with vaccine rollouts may also struggle to keep up. The drugmakers that have already been successful in the variant-focused COVID-19 vaccine market are arguably the most likely to succeed in the variant-focused COVID-19 vaccine market: Moderna and Pfizer (along with its partner BioNTech (NASDAQ: BNTX)). Why is this so? Perhaps most importantly, their messenger RNA technology enables these companies to develop variant-specific vaccines in a timely manner. Moderna and Pfizer have already begun testing their variant-specific candidates.

But, has the rise of coronavirus variants already been factored into these stocks’ valuations? You might think the same about Moderna and BioNTech. Year to date, biotech stocks have increased by nearly 80% and more than 150%, respectively. Pfizer’s stock, on the other hand, is up only 5% this year.

All three of these stocks, however, trade at low forward-earnings multiples. If the coronavirus continues to mutate, necessitating the development of new variant-specific vaccines to avert a pandemic, Moderna, Pfizer, and BioNTech may have plenty of room to grow.