COVID-19 vaccine uses different technology than flu shot

Dear Doctor: Is a COVID-19 vaccine the same as a flu shot? I had a violent reaction to a flu shot in 1976 that continues to have an effect in my body today, and I am 74 years old. I want to get the COVID-19 vaccine, but I fear another severe reaction.

Dear Reader: The vaccine against the coronavirus that causes COVID-19 is not the same as the influenza vaccine. Although each vaccine targets a virus that causes a respiratory illness, they use different mechanisms to prime the body's immune response.

Let's start with the flu vaccine. This is what is known as an inactivated vaccine. It contains a portion of the microorganism that causes the disease the vaccine is targeting. However, the word "inactivated" means that this microorganism has been rendered harmless. It cannot cause disease. When injected, the body's immune system recognizes the inactivated virus as a threat and learns how to mount a defense against it. Then, when the body becomes infected with an actual virus of the same type, it's already primed to fight it off.

The coronavirus vaccines, by contrast, are a class of vaccines known as mRNA vaccines. Instead of a particle of the virus to teach the immune system what to look out for, they use a single strand of genetic code known as messenger RNA. In the case of the new coronavirus vaccines, it's a harmless fragment of the spike protein that the coronavirus uses to penetrate a host's cell. Armed with the molecular code to the spike protein, the body now knows how to recognize and dismantle it. And with its spike proteins disabled, the coronavirus infection is stopped in its tracks.

Considering your experience with the flu vaccine, we understand your hesitancy. However, in your letter you mentioned receiving a number of other vaccines, all without ill-effect. The current guidance for people with previous allergic reactions to a vaccine, or to the contents of the coronavirus vaccine, is to speak with their physician before getting their shot. This, without a doubt, should be your first step.

It's important to note that the coronavirus vaccine can have mild-to-moderate side effects, including pain and swelling at the injection site, chills, fever, headache and tiredness. These can last a few hours or a day or two, and they mean that the immune system is responding to the vaccine and booting up its defenses for future exposure. Everyone who gets the vaccine is asked to remain at the clinic for at least 15 minutes after receiving the shot to monitor for any extreme reaction. These have been exceedingly rare. As part of the vaccination program, the medications and gear needed to assist in case of a reaction are required to be onsite.

Please remember that the clinical trials for the coronavirus vaccines were rigorously conducted to the highest standards. We firmly believe that the short-term inconvenience of the mild side effects of the vaccine outweighs the tremendous benefit of the protection it offers for you and your family, and for the community at large.

Dear Doctor: My husband is 68 years old and recently had an episode of memory loss. He suddenly didn't know where he was. It lasted for about two hours and was very scary. Our son, who is a nurse, says maybe it was transient global amnesia. Can you please tell us something about that?

Dear Reader: Transient global amnesia refers to a sudden episode of temporary memory loss that is sometimes accompanied by confusion. It occurs separately from a condition that could commonly trigger it, such as a head injury, tumor or stroke. The causes aren't yet understood, but it's sometimes compared to the brief and specific bouts of amnesia that can arise after drinking too much, or from drug use.

Someone who is experiencing transient global amnesia, or TGA, is suddenly unable to recall recent events. They can, however, remember who they are, remember the names of familiar objects and recognize family members and people who have a regular part in their lives.

Although an episode of TGA can last up to 24 hours, it is usually much shorter. The average episode lasts about six hours. During the course of an episode of TGA, the individual is unable to either make or store new memories. They often repeatedly ask the same questions, because they are unable to retain the information in the answers that were given. These episodes typically occur in middle-aged and older adults.

While the onset of an episode of TGA is sudden, the recovery is usually gradual. As time passes, the individual will have increasing recall of places and events, until they feel completely oriented again. Once it's over, most people won't be able to recall anything that occurred during the episode. The causes of the condition are not known. A link between migraine and TGA is suspected, but it has not yet been proven. Possible triggers of the condition include physical or emotional stress, physical exertion, pain, sudden immersion in cold or hot water and medical procedures.

Because other serious conditions can share some of the symptoms of an episode of TGA, it's important to seek medical attention. Even though your husband has recovered from his bout of memory loss, it would be wise for him to be evaluated by his health care provider. They will take a medical history and ask for a detailed description of the event.

Since this isn't something your husband can provide, you or someone else who was present will be asked for the narrative. It is likely that a neurological exam will take place. This will check sensory function, reflexes, gait, balance and coordination. Tests to assess memory and recall also will be performed.

Depending on the findings, additional scans, such as magnetic resonance imaging, electroencephalogram or computerized tomography — an MRI, EEG or CT scan — will be used to detect any abnormalities in the brain's blood flow or electrical function. Although alarming, an episode of TGA is not considered to be dangerous. For most people, it's a unique event and is not repeated.