Why 2nd Covid vaccine doses caused worse side effects

I had an unusually tough reaction to Pfizer dose #2. Most people I know had a sore arm and may be felt tired for a day or too. Six hours after I had shot #2, I began feeling sick. The next day I had a 100.6 degree fever – this continued for 3 days and on the 4th day, fell to 99.6 by mid-day and went away late in the afternoon. I had chills (shivering), muscle aches, fatigue, headache and felt similar to having influenza. I had to lie in bed for periods during this recovery. Working was not possible for 4 days.

There is suspicion (as well as one study saying) that those who may have had Covid-19 had worse side effects. That idea is explained here, in this article hypothesizing how people might react to a 3rd dose booster shot.

The culprit was the immune system really ramping up. If the first shot provided the body’s defenses with the scent of a key protein from the SARS-CoV-2 virus, then the immune system was ready to pounce when it saw that spike protein again with shot #2. It was all in the name of building up a lasting and robust blockade in the body, but it did mean some people had quite a hangover after the second dose.

“The immune system goes, ‘I know what this is,’ and attacks it more vigorously,” said Kawsar Talaat, a Johns Hopkins infectious disease physician and vaccine researcher.

Talaat said that it’s possible that, because the immune system is already primed to recognize and target the spike protein, some people could experience something similar after a third dose.

Source: How the risk of side effects could change with Covid-19 vaccine boosters

In the spring of 2020, I was sick for over 2 weeks with symptoms similar to Covid-19 including the “dry cough”. Two of my doctors told me that, but confirmation tests were not available to the general public at the time. A few months after, a doctor suggested I get an antibody test but – we did not know its accuracy at the time, and other than curiosity, knowing the test result would not then be “actionable” so I did not get an antibody test.

The bad reaction I had to the Pfizer vaccine doses hints that perhaps I really did have a typical case of Covid in 2020. But we will never know.