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Healthbeat: What is the difference between a one dose and two dose COVID-19 shot?

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WILKES-BARRE, LUZERNE COUNTY (WBRE/WYOU-TV) — One dose or two? That’s the question many of us have on which vaccine is preferred now that all Pennsylvania adults are eligible to make appointments to get the COVID shot.

With the Johnson & Johnson vaccine on pause nationally to investigate a rare type of blood clot connected to it, the issue is not linked to the fact it’s a single dose.

Even though it’s on pause, you may be wondering why it’s only a one-dose vaccine while the other two emergency use authorized vaccines require two shots.

Each of the vaccines tested during trials proved to be highly effective, although Johnson & Johnson’s was deemed slightly less effective at preventing COVID-19. We spoke with an infectious disease specialist about the COVID vaccine differences.

So what’s the difference between a one-shot vaccine and one that requires a double dose?

“It’s just the way it’s stimulating your immune system to produce an antibody which are the good, protective cells that are needed to protect you in the event you come into contact with the virus,” said Dr. Alison Brodginski, Director of Infectious Diseases for Geisinger Northeast.

Pfizer and Moderna both require two doses. Dr. Brodginski says both use mRNA technology which your cells use all the time to create various proteins that keep you healthy. Even though the second dose has exactly the same potency as the first, each dose has a distinct job.

“And we call it a prime and a boost meaning the first dose primes that immune system and it isn’t until the second dose where you really boost up into those high efficacy ranges,” Dr. Brodginski said.

So why is J&J a “one and done” vaccine and not two doses? Dr. Brodginski says it was not likely the goal of Johnson & Johnson.

“So when they’re going through different types of phases or efficacy trials to determine what’s the most effective amount that’s required in order to produce a nice, good, protective range they go through many different steps,” Dr. Brodginski said.

In the likelihood Johnson & Johnson returns as a vaccine option, Dr. Brodginski makes the following recommendation to people who need a COVID vaccination.

“The best vaccine for you is the vaccine that you can get today,” Dr. Brodginski said.

Since we only have about six months of data on the vaccines in use, we don’t know when fully vaccinated individuals will need another round of shots. Many medical experts believe the protection may last a year or longer but only time will tell.

Much of the data on the effectiveness of COVID vaccines was gathered before variants of the virus emerged and spread. That’s another factor that will need to be taken into consideration on when we may need another round of vaccinations.  

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