: The U.S. Food and Drug Administration (FDA) on Dec. 18 gave the emergency go-ahead for a second COVID-19 vaccine — developed by Moderna — to be provided to Americans across the country. Tens of thousands of health care workers and some nursing home staff and residents have so far been vaccinated with the Pfizer-BioNTech product that received emergency use authorization (EUA) on Dec. 11, and federal officials expect millions of doses of the Moderna vaccine to be shipped on the heels of its EUA to help expand vaccination efforts. Both vaccines use the same basic technology, known as mRNA. These vaccines essentially teach our cells how to make a protein that prompts an immune response without using the live virus that causes COVID-19. Once the immune response is triggered, the body then makes antibodies that would help fight the infection if the real virus does enter our body in the future. But while the two vaccines are very similar when it comes to how safe and effective they are, there are some differences, particularly when it comes to the temperatures at which they are stored, how they are administered and the timetables for when patients need to get their shots. For the latest coronavirus news and advice go to AARP.org/coronavirus. Vaccines have different temperature requirements Pfizer-BioNTech
Vaccine is being shipped in special containers filled with dry ice that can maintain a temperature of less than -94 degrees Fahrenheit and must be stored at that temperature.
Vials may be placed in a regular refrigerator for up to five days. The vaccine must be used between 30 minutes and two hours once it's thawed to room temperature.
Vaccine can be shipped and maintained at standard freezer temperatures of -4 degrees Fahrenheit.
Vials may be stored in a standard freezer for up to six months.
Vaccine can stay in a standard refrigerator for up to 30 days. The vaccine must be used within 12 hours once it's at room temperature.
Significance: Because the Moderna vaccine doesn't need to be transported and stored in as cold a temperature as the Pfizer-BioNTech product, it may be easier to distribute, especially in small communities and rural areas that may not have access to the required refrigeration, says William Moss, a physician and executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health. Preparation varies slightly Pfizer-BioNTech
Once the vial is thawed, the vaccine must be diluted with saline, which is basically salt water, before it can be injected.
This vaccine comes ready to be administered. No dilution required.
Significance: Not much. Having to dilute a vaccine is not uncommon. For example, when health care providers give the measles vaccine, they dilute it. Who can take vaccine? Pfizer-BioNTech
People 16 years old and older
People 18 years old and older
Significance: Not clear. Those under 18 likely won't be eligible to get the vaccine until the spring of 2021 anyway since health care workers, nursing home residents and staff, essential workers, people 65 and older and those with certain health risks are slated to be the first groups to get vaccinated. And, there may be other vaccines available to younger age groups by then. Side effects Pfizer-BioNTech
The most common side effects were pain at the injection site, followed by tiredness, headache, muscle pain, chills, joint pain and fever, according to the FDA.
In the United Kingdom, two health care workers reported severe allergic reactions after being vaccinated; two health care workers in Alaska reported a serious allergic reaction after receiving the Pfizer-BioNTech vaccine.
In the U.S. trial, four people who received the vaccine developed Bell's palsy, which causes usually temporary paralysis in facial muscles
The most common side effects were pain at the injection site, followed by tiredness, headache, muscle pain, joint pain and chills, an FDA analysis found.
Three trial participants who received the vaccine developed Bell's palsy.
Significance: The side effects are basically the same for each vaccine. Moss points out that the number of Bell's palsy cases in both trials is “very small and likely just represents chance,” but says “going forward we'll just need to monitor more carefully and just make sure we're looking for Bell's palsy and make sure that it's not related to the vaccine.” When it comes to the anaphylactic reactions exhibited in Great Britain, one of the participants had a history of allergic reactions. U.S. federal officials have warned health care providers not to give the vaccine to anyone with a known history of a severe allergic reaction to any part of the vaccine, a standard caution for all vaccines. As with the Bell's palsy cases, officials are expected to watch for such reactions. How many shots? Pfizer-BioNTech
Two shots of the vaccine — 21 days apart — are required for it to be fully effective.
Two shots are required, 28 days apart.
Significance: None, according to experts. Each company worked on its own version and decided how many days would be best between shots.
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