Understanding the Key Differences Among the Main Vaccines

white and gold plastic bottle

With three main vaccines available in the United States, Americans are now being inoculated at a staggering pace. Some, however, are wary of the vaccines simply because they don’t understand the options. We’ve highlighted a few of the main differences below:

How Many Shots?

Perhaps the most noteworthy difference between the vaccines: how many times you need to show up. The Johnson & Johnson vaccine stands out due to its single-shot capacity. The Moderna and Pfizer vaccines require two doses, spaced a few weeks apart.

Vaccine Side Effects

Many people are understandably worried about the potential side effects associated with the COVID vaccines. Often, these fears stem from previous bad experiences with the flu shot. In reality, however, side effects are notoriously mild for all three vaccines.

Pain at the injection site is most common, although fatigue and muscle aches also occur in many recipients. With the Moderna and Pfizer vaccines, these symptoms are more severe after the second shot. For most recipients, side effects last just a few days.


The Pfizer and Moderna vaccines resemble one another in terms of protection, perhaps because their messenger RNA technology is so similar. After two doses, the Pfizer option is 95 percent effective. Moderna comes in close behind with a 94.1 percent efficacy following the second dose.

Comparing the efficacy of the Johnson & Johnson vaccine against Pfizer and Modern protection can be tricky, given J&J’s phase three approach of testing for moderate to severe symptoms, as well as timing (with testing occurring after COVID variants began to spread). The J&J vaccine is 72 percent protective against moderate to severe infections in the United States.