Investing for the long term always is the best strategy, no matter what type of stocks you're buying. And relatively young biotech stocks are particularly interesting investments over the long haul. First, they give you the opportunity to watch a company develop innovative and often life-saving technologies -- and that pipeline progress can drive their shares higher. Then, if the company successfully brings products to market, a new phase of growth -- in earnings and share performance -- often begins.

Right now, I've got my eye on two exciting biotech players that would make fabulous long-term investments. One has shown over the past couple of years that its groundbreaking technology works -- and might be applied across many indications. The second may be close to launching its first product.

1. Moderna

If you bought Moderna (MRNA -1.69%) shares a few years ago, you would have benefited from the company's first big growth phase. The biotech brought its coronavirus vaccine to market and generated billions of dollars in revenue. The stock also climbed.

Now that demand for the Spikevax vaccine is on the decline, some investors may feel that it's too late to buy Moderna shares. It's true that Moderna's COVID-19 vaccine sales are unlikely to repeat their 2021 and 2022 performances in the coming years. But that doesn't mean the company's growth is over. In fact, a new phase may be just ahead.

The coronavirus vaccine proved Moderna's messenger RNA technology works -- and the biotech uses that same technology throughout its pipeline. The company has 48 programs in development across many indications.

Three of its candidates, each in phase 3 trials today, may reach commercialization within the next few years: vaccines for flu, respiratory syncytial virus (RSV), and cytomegalovirus (CMV). Each of these indications represents a blockbuster opportunity.

The vaccine with the shortest potential path to market is its RSV candidate. Moderna aims to file for regulatory approval of it in the first half of this year. The company is preparing for a 2024 launch.

It's also important to remember that, thanks to its COVID-19 vaccine revenue, Moderna has more than $18 billion in cash on the books that it can use to support the growth and development of its pipeline.

All of this means growth is far from over for Moderna. And that makes it a great stock to buy now and hold onto for the long term.

2. CRISPR Therapeutics

CRISPR Therapeutics (CRSP 0.66%) has reached the most exciting point in its story so far. The biotech has submitted its first potential product to regulators in Europe and the U.K. -- and it's set to complete its U.S. regulatory submission for that candidate therapy by the end of the first quarter.

CRISPR and partner Vertex Pharmaceuticals hope to soon bring this candidate, exa-cel, to market around the world.

Exa-cel is a treatment for the blood disorders beta-thalassemia and sickle cell disease. It could be a blockbuster revenue generator for CRISPR for two reasons. First, today, there are limited treatment options for either beta-thalassemia or sickle cell disease. Patients usually rely on blood transfusions to manage their conditions, and a new treatment likely will be welcome.

Second, exa-cel is a one-time treatment that is intended to provide a functional cure to those conditions. It's easy to imagine doctors and patients flocking to it.

This potential approval is key for another reason. It would be seen as a validation of CRISPR's technology. In exa-cel, the companies used CRISPR's method of gene editing that "fixes" the faulty genes involved in the development of disease. CRISPR uses gene editing across its pipeline. This doesn't mean every candidate therapy that uses this technology will be successful, but it does offer reason to be optimistic about the company's work.

Speaking of other candidates, CRISPR has a second one that's not too far behind exa-cel on the clinical trial path. It recently began a phase 2 trial for immuno-oncology candidate CTX-110. Data from that study could be used to support a regulatory submission.

CRISPR is just at the beginning of a long-term growth story that could drive significant share price growth, making it a great biotech stock to buy right now.