Here’s why doctors say you shouldn’t get a COVID-19 booster shot — yet

A health care worker prepared a dose of the Pfizer-BioNTech vaccine at Boston Medical Center.Adam Glanzman/Bloomberg

With the Delta variant driving a surge in COVID-19 cases, some vaccinated people are scrambling for an extra layer of protection in the form of a booster shot.

But public health officials and doctors say that while it’s possible that an extra vaccine shot could boost immunity, distributing boosters now could have unintended effects, both on a personal level and from a global health perspective. No vaccines have yet been approved in the United States for use as booster shots.

The head of the World Health Organization last week called for a moratorium on booster shots, urging countries to wait until vaccinations increase in places with less supply. And although shots are plentiful in the US, doctors warn that dangerous new variants will emerge if the rest of the world doesn’t get vaccinated.

“There are a lot more letters in the Greek alphabet,” said Dr. Mark Siedner, an infectious disease clinician at Massachusetts General Hospital. “This won’t be the last of the variants if we don’t get most of the world vaccinated.”

Here are some of the things that Siedner and other experts said people should consider before seeking a booster.

Your current vaccine is still good

Current research says that if you’re fully vaccinated, you’re well protected against COVID-19 and are especially safe from getting very sick.

“The data now show[s] pretty clearly these vaccines after the normal recommended doses — one if it’s Johnson & Johnson, two if it’s the others — are extremely effective, and they are preventing hospitalizations and preventing deaths,” Siedner said.

Though breakthrough infections have occurred, infections are far less common among people who are fully vaccinated. And those cases tend to be milder.

Out of the 4,291,441 people who were fully vaccinated by July 16 in Massachusetts, less than 1 percent have had a breakthrough COVID case, according to data released by the Department of Public Health Aug. 3.

Booster shots aren’t authorized

While the US vaccines remain effective, there have been some studies that show the Delta variant may reduce their efficacy to some degree. And immunity also may wane over time.

Scientists and some vaccine manufacturers say that means boosters may be required at some point. But the US Food and Drug Administration and the Centers for Disease Control and Prevention have said such shots aren’t necessary right now, and boosters are not covered by the FDA’s emergency use authorizations for vaccines.

A spokeswoman for the Massachusetts DPH wrote in an e-mail that boosters are not authorized under Massachusetts agreements with vaccination providers.

Providers, including Walgreens, CVS, and several major health care systems, are not giving out boosters, according to STAT.

There are some instances in which health care providers have offered additional shots. Zuckerberg San Francisco General Hospital has allowed people who received the Johnson & Johnson vaccine to get a dose of the Moderna or Pfizer vaccine — a decision that has received pushback from the White House.

It appears the FDA may act soon to authorize booster shots for people with weakened immune systems. Some doctors already have begun offering additional shots to people in that population.

Dr. Cassandra Pierre, the associate hospital epidemiologist at Boston Medical Center, said her hospital allows for an extra dose for people in certain immunocompromised groups — such as individuals who have received organ transplants — who do not experience full immunity after receiving a complete dose. But these are rare exceptions.

“There is some data that . . . strongly supports getting a third dose can lift that group from being not fully or not considered people vaccinated based on antibody responses to a better antibody response, potentially a therapeutic response,” she said.

The science isn’t there to support booster shots now

For most people, there is no concrete data available that studies the effectiveness of boosters, doctors say. People will have to wait until the fall for any official recommendations on booster shots as clinical trials continue, they added.

Dr. Daniel Kuritzkes, the chief of the division of infectious diseases at Brigham and Women’s Hospital, said doctors need to know more about the efficacy and logistics of boosters.

“You can certainly increase antibody levels by boosting — whether that actually results in better protection and when the right time to boost might be is completely unclear,” he said.

Siedner said that there is no data now that shows booster shots are “actually helpful” to the general population who develop immunity after a normal dose of the vaccines.

Doctors stress that people still need to wait and allow others to get their preliminary shots.

“It’s very possible that things like the Delta variant do change the equation . . . and boosters are needed,” Siedner said. “I think there’s a very strong likelihood that will be the case in the future, but right now the best way to stop people from getting sick and to stop new variants like the Delta or potentially even more variants from emerging is making sure people get one and two shots, not making sure people get a third shot.”

Even if the supply in the US is plentiful, there is a massive global need for vaccines

Doctors say that more people need to be vaccinated to protect the world from future variants of COVID-19.

Due to the supply of vaccines in the US, Siedner said policymakers have a “moral imperative” to rethink where those vaccines should go and whether they should end up untouched on shelves across the country.

Pierre said booster vaccines right now present a host of logistical challenges without more stock.

“It’s true that the expiring stock here is not going to be transferrable and so that could certainly be used for booster vaccines,” she said. “I don’t necessarily think there is enough to cover everyone who is interested in having a booster vaccine or if those expiring stocks are in the right areas.”

Expiring vaccine stocks are in areas that are largely unvaccinated, she said, and it won’t be feasible to transfer them from these places to localities with high demand for booster doses.