Studies of Pfizer's coronavirus vaccine showed no major safety concerns, and regulators at the US Food and Drug Administration cleared the shot on Friday for emergency use.
The vaccine is highly effective and safe, based on a clinical trial of more than 40,000 participants.
There were temporary side effects that are generally expected with most vaccines. Common side effects were pain at the injection site, fatigue, and headaches.
US regulators on Friday greenlit the Pfizer-BioNTech coronavirus vaccine for emergency use, kicking off the biggest vaccination drive in US history.
Their decision was based on a detailed review of evidence showing that the shot is safe and highly effective, and likely to be an important tool in combatting the pandemic. Pfizer and BioNTech, its German biotech partner, tested their vaccine in a global study that randomized more than 40,000 volunteers to either get two doses of its vaccine or two doses of a placebo injection.
Still, most immunized volunteers had temporary side effects shortly after being vaccinated, including fatigue, headaches, and pain at the injection site.
Now that the Pfizer vaccine is authorized, people are likely to start getting shots next week. US health officials have said that healthcare workers and residents of long-term care facilities should be first in line to get the shot.
Over the coming months, Pfizer's vaccine, and potentiall others, will become more widely available. Here are the side effects to know about from Pfizer's shot.
Common side effects included fatigue and headaches
People under 55 years old reported more side effects than older volunteers. These side effects were expected with a vaccine, typically appearing within a couple of days of receiving a dose and lasting for only a day or two on average.
Common side effects people reported after getting Pfizer's vaccine were:
Pain at the injection site (84%)
Muscle pain (38%)
Joint pain (24%)
Pfizer and the FDA also provided information on the severe side effects that volunteers experienced. In general, those are side effects that are so bad that they stop people from performing normal activities.
Most of the severe side effects occurred after participants got the second dose, and these side effects were more common among younger participants.
Some people experience severe fatigue and headaches after getting the shots
Among people aged 18 to 55, 4.6% reported severe fatigue after getting their second injection, and 3.2% had severe headaches.
Fevers were also common in that age group; about 15.8% of the volunteers had a temperature of at least 100.4 degrees Fahrenheit after their second shot.
Among volunteers older than 55, 2.8% reported severe fatigue, 0.5% experienced severe headaches after the second dose, and 10.9% had a fever.
Scientists at the FDA and at Pfizer and BioNTech have been poring over the data to see whether there were any unexpected safety concerns. Encouragingly, they said in documents released Tuesday that they didn't find anything that caused concern.
FDA regulators noted a "numerical imbalance" in cases of Bell's palsy, a condition that temporarily weakens face muscles: There were four cases of Bell's palsy among the 20,000-plus people who got Pfizer's vaccine, compared with no cases in the placebo group.
But the FDA said this frequency of Bell's palsy cases among those who got Pfizer's shot was not any higher than what would be expected for the general population.
Pfizer will continue to study the shot
Agency scientists also said that the vaccine's safety profile was "generally similar" across different ages, genders, ethnicities, racial groups, as well as across people with or without health conditions and people with or without evidence of a previous coronavirus infection at enrollment. The only exception, they said, was that younger people tended to have more frequent side effects.
The long-term safety of the shot remains unknown, because most people in the trial have been monitored for only a few months. Typically, according to experts, the vast majority of side effects - but not all - occur within 42 days of getting a vaccine.
Pfizer, as well as providers giving the shot, are required to track and report any serious safety problems with the vaccine. The drugmaker is also required to conduct studies to look for any safety issues that may crop up.
Shortly after the UK started to give Pfizer's shot to healthcare workers and older people, authorities said that people with a history of serious allergic reactions to other medicines or food should not get the vaccine. The warning followed two reports of adverse reactions in healthcare workers who have a history of severe allergies.
The FDA issued a narrower warning, saying only that people shouldn't get Pfizer's shot if they've had a severe allergic reaction to a previous dose of this specific vaccine or to one of its ingredients.
This article was updated on December 12 with the FDA's decision to authorize the vaccine.
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