COVID-19 shortly after vaccination - better/worse/same?
March 29, 2021 9:26 AM   Subscribe

Do we know anything about how COVID-19 makes people sick differently (or not) if they catch it soon after vaccination? This is hard to search for information.

Web searches mainly return information saying that yes, you can still catch COVID-19 and get sick in the time before the vaccine-induced immunity kicks in. But that's not my question.

I'd like to know how the progression of COVID-19 changes if a person catches it a few days or a week after vaccination, or between doses for shots with two doses.

Do we know anything? Are there any expectations from other diseases? Would it be roughly the same as if the person weren't vaccinated? Would it be worse because the person's immune system is busy (or something) after the vaccination? Would it maybe be not as bad because the person's immune system is already gearing up with antibodies to the spike protein?
posted by medusa to Health & Fitness (7 answers total)
I think what I've read is that it's not as bad, but I don't have any specific citations to give you.
posted by jenfullmoon at 9:45 AM on March 29, 2021

Best answer: I believe that in general we would expect you to be slightly better off because your immune system is already gearing up.

More specifically, if you look for example at this cohort study of the Pfizer vaccine and scroll down to the graphs, the number of incidences of infection in the vaccinated and control groups track extremely closely for the first seven days or so and then start to diverge. There's no data in these graphs about severity, just incidence, but it's reasonable to use incidence as a proxy for severe disease and death.

I am not a doctor, epidemiologist, or immunologist!
posted by mskyle at 10:04 AM on March 29, 2021

Best answer: I mostly agree with mskyle above, but I'd say instead of slightly better it's probably much better. More data would be nice.

We were talking about this at work at a virtual happy hour last week (I'm a chemist in a research department that's done a lot of antiviral work). A colleague had just attended a talk and put up a chart that was quite promising, showing the divergence between vaccinated and unvaccinated people by day 7. [Pretty similar to some in mskyle's link!] Unvaccinated people continued to get it, vaccinated people levelled off at that point almost completely. Also this was based on symptoms, so many people who were getting sick days 1-6 were infected before vaccination.

With limited data it's always good to compare against theory, and in this case the data doesn't contradict the biological understanding--the infection is a race between your immune system and viral reproduction, and if you immune system gets started two days early it has a head start.
posted by mark k at 10:43 AM on March 29, 2021 [1 favorite]

This isn't a directly-on-point answer to your question. But if you are asking this because you're feeling like royally processed crap after your vaccination; and it's lasting longer than the supposed 1-2 days; and because of that, you're wondering if you were infected at the vaccination site -- I know that for me, the post-injection lasted longer but eventually has mostly cleared out. (And this was for shot 1, so I'm expecting things to be a little cruddier for shot 2.)
posted by metabaroque at 11:15 AM on March 29, 2021

I am not sure if this is directly on point, but a new CDC study looks at the effectiveness of one shot of both Pfizer and Moderna or the time between shots. 80% effective it says.
posted by AugustWest at 12:21 PM on March 29, 2021

Best answer: The studies that have looked at the period between the first and second shots have all found a positive effect in reducing both number of infections and seriousness of the disease. A typical way to look at that is (like the CDC study AugustWest mentioned above) looking at the period starting two weeks after the first dose until the second dose is given.

A question is, does the immune response grow steadily over 2-3 weeks, does it kick in rather suddenly after a certain period, or what?

This cool little study looks at exactly that--how high or low do antibody titers look at various periods after the first dosage.

If you look at Figure 1, that tells the story.

- 0-4 days after the first dose, no one had a noticeable response

- 5-8 days after first dose, a small minority (10%?) of the patients had a good response

- 9-12 days after the first dose, a clear majority (75%?) of patients had a good response

- From that point, the number of people with a good response gradually increases, and by 21-27 days after the first dose, all patients had a good response

Note that this applies to people who not previously had Covid-19. Those previously infected people all had a good immune response within 5-8 days of the first dose (and had no noticeable improvement after the 2nd dose--in contrast to non-infected people).

So short answer (for those not previously infected with Covid-19): You might have some response/protection within 5-8 days, far better protection 9-12 days, and full protection (as much as this dose will give you) by about 21 days.

An interesting note: Just looking at the data in the study, it does not look like antibodies levels gradually-gradually increase over 21 days. Rather, for each person the levels seem to increase rapidly over a period of just a few days. But for some people this happens as soon as 5 days, others as late as 21 days after the shot.

Also noted in the study: 14 days after the second dose, patients have around 3X the antibodies they achieved via the first dose. Plus, after the second dose, T-cell activity is measurable--whereas it isn't after just the first dose.

T-cell activity is vitally important to long-lasting immunity. So getting that second dose seems to be quite helpful and important.

Caveat: The above study measures antibody levels and antibody levels are not a perfect indicator of immunity or immune function. So take with as many grains of salt as required. But the study does give some idea of how immunity might develop over time after a vaccine dose.
posted by flug at 2:34 PM on March 29, 2021 [2 favorites]

Response by poster: This is just a curiosity question based on reading about people who get sick soon after vaccination. Thanks for the links.
posted by medusa at 5:10 PM on March 29, 2021

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