If you have already had Covid, would your reaction to a vaccin be likely to be less severe?

I’m kind of prone to making up medical theories that sound logical, but, as I have no medical background, turn out to have little relation to reality. This is the latest. So if someone, either knowingly or unknowingly, had already had Covid19 and then had a vaccin shot, would they be less likely to suffer side effects like fever? The reason I think this is because if someone has already had it, they have a lesser (or no) reaction to the real thing - leaving mutant strains out of the equation - so when the vaccin is administered, would their body would just go “oh yeah, that thing, again” and get rid of it without a fuss? Does anyone know if this is at all possible or completely off the mark.

Like so many things covid it seems to be a bit of a crapshoot.

There have been reports of people who have had covid having stronger side effects to the vaccine than people who haven’t had covid. But the side effects suffered range from “none at all” to “in bed for a couple days” (a very, very few - about one in 500,000 - result in a trip to the hospital due to, depending on the vaccine, allergic reactions or blood clot problems)

Speaking from my own experience, as someone who had diagnosed covid, after the first shot my arm hurt for about a day and a half and I felt fatigued for about 2-3 days. After my second shot my arm hurt for about a day, I felt fatigued for a day, and mild chills but both the arm pain and tiredness, although of shorter duration, felt more intense the second time around. Neither, however, was horribly bad, stopped me from doing stuff, and nowhere near as unpleasant as actual covid.

A friend of mine who has not had actual covid took the day off after the first shot with aches, chills, and fatigue. After shot number two he went to bed for 3 days with fever, aches, chills, and exhaustion. This is a guy who normally never took a day off for being sick.

In general, many people report side effects from the second shot being worse than the first, and indeed I was cautioned about this when getting the second shot. In general, people who have had covid have stronger side effects than those who haven’t though, as I said, it’s not as bad as actual covid (in general - with so many people having or not having the virus, and getting the vaccine, and different vaccines, there are exceptions all over the place).

Thanks for that.

I seemed to have no side effects at all and I wondered why, but I spoke to soon. Came down with low-grade fever, aches and fatigue a few hours after writing. Which means we know now…nothing much.

Good question. The reactions to both COVID and vaccination seem to vary hugely. What I read somewhere was that nurses who had been exposed to COVID but did not get affected had more antibodies and had stronger reactions when vaccinated. That sounds feasible.

I got the Pfizer vaccine a week, having kept well out of the way of any stray viruses, and had a slightly sore arm for two or three days. Well, tender rather than sore. No other reactions at all. A month from now I will know if the second shot provokes a stronger reaction.


My 21 y/o grandaughter is an EMT/firefighter. She got Covid summer 2020 but fortunately the “prince Charles” variety. She was vaccinated in February and got her second shot early in March. She said her side effect was the day after the second shot she slept practically all day.

The rule for Tuberculosis vaccination (BCG) is

People with a past history of TB should not receive the vaccine . This is because they have an increased risk of adverse reactions to the vaccine.

BCG Vaccine (TB vaccine) | Vaccine Knowledge (ox.ac.uk)

Also, people currently being treated for TB should not be vaccinated, (because the treatement ‘treats’ the vaccination the same way it treats the disease).
Tuberculosis | The Australian Immunisation Handbook (health.gov.au)

The evidence of the COVID vaccine trials and the current vaccination role-out is that COVID vaccination is not causing an exaggerated immune response in people with pre-existing COVID immunity.

And there is currently no effective treatment for COVID, but vaccination would probably not be offered to someone currently being given anti-virals.

I think it’s interesting, because to me logic would dictate that if the vaccin teaches your immune system how to fight a certain intruder, it would stand to reason that if it has already seen and fought off this intruder, it would already “know” how to “fight” the vaccine too and so react less in the same way it would react less to the real thing. But obviously this is an oversimplification of mine.

It seems to be the other way round - that if you’ve had covid, you might have more side effects. The data so far is inconclusive.

However, when I was talking to someone from my rheumatology team (I mean I’m a patient - I have a named doctor but often actually talk to someone who works under him) it came up that I’d had a bad reaction to the vaccine and had had covid, so was at the extremely low end of risk for actually catching it again.

She was completely unsurprised and said she’d experienced the same - virtually no symptoms for the disease, bad symptoms for the vaccine. I had an almost identical conversation with my health visitor/nurse, and similar online.

So whether it’s true or not, there’s enough anecdata that at least some medical professionals believe it.

I imagine (not supported by citation), that COVID vaccines are mostly if not entirely targeting one specific point on the COVID virus. So your natural “exaggerated immune response” would only be invoked to the extent that you had acquired natural immunity to that one specific point.

BCG (the TB vaccine) is an attenuated tuberculosis bacillus, containing a broad spectrum of points you might be immune to, so a strong immune response to it might be reasonably expected in a person with a currently activated natural TB immune response.

Specifically, the spike protein is used by the mRNA vaccines and (I think) J&J.