When there are bargains on stocks with long-term appeal, astute investors make sure to get a few shares while the getting is good. And if you're looking for exposure to growth, the stocks listed on the Nasdaq-100 Index -- which is part of the Nasdaq Composite -- is a good place to start. In that vein, let's discuss a pair of monster growth stocks that are worth buying hand-over-fist right now.

A pair of scientists review data on a computer at a lab bench with some plant samples in beakers nearby.

Image source: Getty Images.

1. Moderna

In truth, Moderna (MRNA -2.52%) is a bit of a contrarian purchase at the moment as nobody expects it to one-up its 2022 top line of nearly $19 billion now that sales of its coronavirus vaccine are expected to fall to as low as $5 billion in 2023. And there's little to suggest that demand for its shots will surge to reach the heights of the last couple of years ever again.

That's why its valuation is so low. Its price-to-earnings (P/E) ratio is a mere 7.6, a fraction of the market's average P/E of 23.

But farsighted investors know that near-term problems often have little to do with a company's long-term performance as an investment, and that's certainly the case with Moderna. It isn't as though the coronavirus jab is the last medicine it'll ever commercialize, and it actually has quite a few potentially lucrative programs working their way through clinical trials. 

Take for instance its phase 2 therapeutic vaccine program for myocardial ischemia, which aims to treat the condition before it can develop into a heart attack. That could find a huge market if it's proven to be safe and effective. Meanwhile, its personalized cancer vaccine (PCV) in phase 2 trials, being developed with the help of Merck, could also be enormously successful.

Those are just two programs out of its total of 48 -- and there's a high chance Moderna will succeed in bringing a handful of its later-stage infectious disease candidates to the market before either of the two potential moneymakers. With so many different opportunities lined up, buying this stock looks like a smart move even if it might take a couple of years to pay off.

2. Apple

The investment thesis for Apple (AAPL -2.88%) is quite different than the one for Moderna. You should be scrambling to buy Apple stock not because of its pipeline of groundbreaking new products, but because it barely needs to invest in developing new products to retain its market share and remain profitable thanks to the power of its brand.

Most of the company's products are designed to yield significant sums of recurring revenue. For example, its iCloud storage service and its other subscription services yielded more than $78.1 billion in 2022 alone, a rise of 14% compared to a year prior.

Plus it has more than two billion devices like computers and iPhones being used in the wild, and every last one of them will eventually need to be replaced by a newer and slightly faster version of itself. Even during the challenging consumer purchasing environment of the last couple of years, its sales of Mac computers still rose by 14% in 2022, topping $40.1 billion.

And over the last 10 years, Apple's quarterly research and development (R&D) expenses were, on average, only 5.3% of its quarterly revenue. In that same period, shareholders got to experience a total return of above 1,020%, and its grip on the U.S. smartphone market has only increased since then. So it isn't as though Apple is in a fierce R&D race with competitors that'd compress its margins over time.

To top it off, Apple is one of Warren Buffett's favorite investments, and it's also his largest holding. And that's yet another reason to buy it today