Late Thursday evening, CDC chief Rochelle Walensky recommended that Pfizer booster shots be offered to people over the age of 65, those at risk of severe health problems, and people who are at high risk of coming into contact with the coronavirus at work.
The announcement capped off weeks of fierce disagreement among scientists — including within the federal government — about whether boosters were needed and who should get them.
So do you need to get a shot? How can you get one? And what the hell was all the confusion about? Here's everything you need to know:
First off, what is a booster shot?
A booster shot is an additional dose of a vaccine intended to "boost" the immune response to a particular virus. Booster doses are routinely administered for many vaccines.
Pfizer's COVID-19 vaccine is administered as a series of two doses, spaced three weeks apart. The booster dose now being recommended for some people should be taken at least six months after your second shot of the Pfizer vaccine. The six months are needed to make the booster most effective, according to National Institute of Allergy and Infectious Diseases chief Anthony Fauci.
Who qualifies for a booster?
So far, only people who have already received two doses of the Pfizer vaccine qualify for a booster dose. The CDC recommends that the following groups should get a Pfizer COVID-19 booster shot:
people 65 years and older and residents in long-term care settings
people 50–64 years old with underlying medical conditions
The health agency also said that that the following groups might want to consider getting a booster but should talk to their physicians about their individual benefits and risks:
people aged 18–49 years with underlying medical conditions
people aged 18-64 years who are at increased risk for COVID-19 exposure and transmission because of an occupational or institutional setting
In its authorization on Wednesday, the FDA stated that high-risk jobs included healthcare workers, teachers, people who work in daycare facilities, and grocery workers. Those at risk in institutional settings include people in correctional facilities or homeless shelters.
People who have compromised immune systems have already been authorized to receive a third shot since August.
In a press briefing on Friday, White House coronavirus czar Jeff Zients said that the new recommendations mean that 20 million Americans are now eligible for booster shots. Another 60 million people will become eligible over the coming months.
Why did the CDC and FDA recommend booster shots for some people?
In several days of meetings over the last two weeks, expert panels evaluated a request from Pfizer to offer boosters to everyone 16 and older. To make a decision, advisers to the health agencies looked at studies showing how much immunity to COVID-19 is waning over time.
It is very normal for immunity to a disease to decrease over time. Experts on both panels repeatedly stressed that while it's been shown that antibody levels decrease over time after receiving a COVID vaccine, the vast majority of vaccinated people who get infected are still protected from getting very sick or being hospitalized. That's because longer-living "memory" immune cells still offer strong protection against the virus.
Although there’s so far no clear evidence from the US that waning immunity is leading to an increase in severe illness and hospitalization among vaccinated people, data from Israel shows that people age 60 and older who had their second Pfizer dose in March were less likely to get severe COVID compared to those who got their second dose in January. That trend was similar for younger people.
Since older people and those with underlying health issues face the highest risk of severe illness, the FDA and CDC expert panels recommended that they get a third dose. The FDA authorization, as well as Walensky's recommendation on Thursday night, also extended this to people who work in settings where they are at high risk of coming in contact with the coronavirus.
Does a booster shot come with any extra side effects?
Although this data is still limited, the side effects Pfizer reported were very similar to those experienced with the first two doses of the vaccine. Fatigue, headache, chills, and muscle pain were the most common symptoms.
The FDA has so far only authorized boosters for those 18 and up who fall into the eligible categories above; Pfizer has still not collected safety data on boosters for those aged 16 to 17.
When can you get a booster shot?
According to Zients, eligible individuals can start receiving COVID-19 booster shots as of Friday. Some people will get boosters as early as "this afternoon," he said.
Pharmacies, doctors' offices, and other health sites will be administering additional doses, much like they did for the first and second shots. Call your pharmacist or physician to find out about scheduling, and make sure to bring along your vaccine card.
What if you got the Moderna or Johnson & Johnson vaccine?
So far, only people who received two doses of the Pfizer COVID-19 vaccine are eligible for booster shots.
Earlier this week, Johnson & Johnson submitted data to the FDA showing a booster shot increased the effectiveness of its one-dose vaccine, according to a company news release. Moderna submitted its own data to the FDA for authorization earlier this month.
In a statement released Thursday night, CDC chief Walensky said that the health agencies were pushing forward to look at the data for these vaccines as well. "We will also evaluate with similar urgency available data in the coming weeks to swiftly make additional recommendations for other populations or people who got the Moderna or Johnson & Johnson vaccines," Walensky said.
Why was there so much fighting over booster shots?
There are two main reasons why scientists were fighting so much over the need for boosters.
First, many health experts — including top officials at the FDA and the World Health Organization — argued that the primary goal should be vaccinating as many people as possible worldwide to prevent deaths and the emergence of new, more dangerous variants. The WHO has called for a "booster shot moratorium" to try to vaccinate more people in the developing world.
And within the US health agencies, much of the disagreement centered over whether boosters were necessary since the vaccines still provide strong protection against severe illness. In the end, the agreement was that those at the highest risk should get an additional shot rather than the general population.
Do other countries offer booster shots?
About 20 countries offer booster shots to part of their population, typically older people, healthcare workers, and people with compromised immune systems. Israel offers boosters to everyone, as does Hungary.
The United Kingdom approved booster shots for people 50 and older, as well as vulnerable groups, such as people with cancer with compromised immune systems, and began its rollout last week.
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