What you need to know about COVID-19 vaccines in the US

It’s clear that COVID-19 vaccines are playing a large role in restarting travel and, in some cases, will be required by certain destinations or travel providers for entry or to avoid testing and quarantines.

A major hiccup came on April 13 when the U.S. Food and Drug Administration (FDA) and U.S. Centers for Disease Control and Prevention (CDC) announced that they recommended pausing the Johnson & Johnson vaccine after several women developed a rare blood clot disorder linked to the vaccine.

The CDC is once again recommended the shot as of April 23, but it will now come with a warning label about the "exceedingly uncommon, but potentially dangerous" clotting, after further analysis.

The Johnson & Johnson vaccine is one of three approved for emergency use in the United States; the other two are Pfizer-BioNTech and Moderna. There are also several more vaccines either in development or available worldwide, such as AstraZeneca in the United Kingdom, the Sputnik V in Russia and China’s CoronaVac.

According to figures from the CDC, nearly 130 million Americans have been fully vaccinated.

You likely won’t have a choice in which vaccination you receive when it’s your turn in line if you opt for the vaccination at your local health department. However, you can "shop around" for a vaccine appointment at various pharmacies, some of which -- such as Walmart and CVS -- will tell you which vaccine they are giving when you make your appointment.

No matter which vaccine you get, when you get it will determine when you can travel again. Here’s what you need to know about the COVID-19 vaccines currently available in the U.S.

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What are the differences between the three vaccines?

Pfizer-BioNTech

The Pfizer-BioNTech vaccine was the first vaccine approved in the U.S. after the Food and Drug Administration (FDA) issued an emergency-use authorization in December.

About 95% effective at preventing the COVID-19 illness, according to the CDC, this vaccine requires two doses, which must be taken 21 days apart. It’s been reported that side effects like fever and chills were more prevalent after the second dose.

"[Two] is a tried-and-true vaccination approach," said Dr. Jenny Yu, the senior manager of medical integrity at Healthline (which is also owned by TPG's parent company, Red Ventures) in an email. Hepatitis A and B vaccinations, she said by way of example, are given in two doses. "That approach allows for the body’s defense to be prepared and ramp up the appropriate response for developing antibodies."

The Pfizer-BioNTech vaccine is currently the only vaccine approved by the FDA for children as young as 12.

Moderna

Like the Pfizer vaccine, the Moderna vaccine also has to be taken in two doses, 28 days or one month apart.

The Moderna vaccine is 94.1% effective at preventing COVID-19 in people who received two doses. More than 25% of the people who participated in clinical trials were healthcare workers. Like the Pfizer vaccine, side effects were more common after the second dose of the Moderna vaccine.

As with the Pfizer vaccine, it also takes people who receive the Moderna vaccine about a week to develop immunity, said Dr. Yu.

The Moderna vaccine could also soon be approved for children between the ages of 12 and 17.

Johnson & Johnson

The newest vaccine available is Johnson & Johnson (J&J), which was approved for use on Feb. 27.

This vaccine differs from the other two in that only one shot is required. The Johnson & Johnson shot has made news for having a lower efficacy rate than the Moderna and Pfizer vaccines — more than 66% effective in clinical trials at preventing laboratory-confirmed COVID-19 illness, according to the CDC.

The FDA and CDC announced on April 13 that it recommended pausing the Johnson & Johnson vaccine after six reported cases of a rare blood clot were discovered. According to the CDC, the six cases occurred among women between the ages of 18 and 48, and symptoms occurred six to 13 days after vaccination.

But the CDC is once again recommending the shot, though it will now carry a warning about the clotting.

The J&J shot is also being studied for adolescents.

Can I pick which vaccine I get?

Some states, such as Indiana, publish which location has what vaccine — but many locations do not advertise this information.

If you have questions about a particular vaccine, you can ask your primary care physician or the person administering your vaccine for more information. Either way, experts recommend getting whatever vaccine is available when it's your turn to be vaccinated.

“Given that we want to achieve herd immunity as quickly as possible," Dr. Yu said, "people should take the vaccine that is available to them.”

When can I travel again after getting vaccinated?

The CDC says people should wait two weeks after getting the final COVID-19 vaccine dose to travel, as it takes time to build immunity against the virus.

“Traveling with vaccinations ... gives people a sense of reassurance,” said Dr. Yu. But she says wearing a mask, maintaining physical distance from others and practicing hand hygiene is "still important in protecting others.”

Although the CDC in early April announced that fully vaccinated Americans can travel at “low-risk” to themselves, the U.S. State Department last month added approximately 80% of the world’s countries to its highest advisory — Level 4: Do Not Travel — and recommends U.S. citizens reconsider traveling abroad.

Can I test positive for COVID-19 if I’ve been vaccinated?

Experts are currently looking at how receiving the COVID-19 vaccine could affect antibody testing results. The CDC says you may test positive on some antibody tests, which test to see if you’ve been previously infected.

“There are still the rare incidences of testing positive before vaccine immunity is in place from an infection,” said Dr. Yu. “It can be for people who are not fully vaccinated with the two doses.”

Will a vaccine be required to travel?

Having received a COVID-19 vaccine could very well be a new requirement for entry to some destinations, similar to the way proof of yellow fever vaccination is already necessary to travel to some countries.

Several countries have indicated that they’ll allow vaccinated travelers to skip mandatory quarantines. And certain destinations and travel providers have indicated the vaccine could even be a requirement.

Related: Where you can go with a vaccine passport: A country-by-country guide

Bottom line

COVID-19 vaccines are key to restarting travel.

You may not always be able to choose which vaccine you get, but all three vaccines are proven to prevent serious illness and death from COVID-19.

And experts like Dr. Yu say having any vaccine in our system will help the entire world regain some sense of normalcy.