Why do some vaccinated catch COVID and others don't ?

[strugglingmummy2021]

Just curious if anyone can explain.

Say two people are vaccinated and exposed to the virus, one gets COVID and the other one doesn't, why is that ? Did the one who got COVID not have antibodies ?

Or say I'm vaccinated and don't catch it the first time I'm exposed, but then I keep being exposed many times and eventually it ' breaks through '- as I've had so much exposure ? Or is the fact that I didn't catch it the first time, a sign that I'm unlikely to catch it if I'm re-exposed ( putting all the current talk about length of immunity aside- or maybe not.. )

Just wondering if anyone knows?

I think it's exactly the same as if you are unvaccinated and exposed to COVID (or any other virus). Some exposed people will catch it and some won't. No virus is 100% transmissible. Vaccinated people will be less likely to catch it, but there's still a risk.

It's thought that immunity from the vaccines (or from contracting COVID) is likely to wane over time in most people. Some produce a better immune response to the vaccine and are less likely to catch it than others.

Even without vaccines, if one member of a household catches COVID it isn't 100% certain that everyone else in the household will. Just as with the vaccines it isn't 100% certain that it won't - it's just more likely that you won't.

Viral load (how heavily exposed you are) and general health will also affect how likely you are to catch it.

I would like to know this. My friend and her 2 kids had covid about 6 weeks ago and she was quite unwell so her DM moved in and isolated with them to help. I was sure she would catch it but she didn't. She said she is sure its from the vaccines but who knows. Even pre vaccines some people didn't catch it despite close contact

Anncedotely in the 4 families I know that have had covid, two of the adults had az and they were they only ones that didn't catch it despite sharing a bed with their partner and not isolating from dc 🤷‍♀️

So even with natural immunity then.. there are lots of reports of people just not getting it, even though they were exposed in the same way as another person who did get it.

I have read various theories in the news about why some people caught it or not. But I think they've just been speculative. For example the flu vaccine may have offered protection or the TB vaccine etc. Or a previous infection from another coronavirus. That was another theory I read ages ago as to why some people don't get sick with it. Who knows ! It's ' novel ' after all.

It chimes with pre-Covid experience, though, that just because one person in a household / group gets a bug, it isn't inevitable that others will, and it isn't always predictable who will / will not suffer.

Despite my mum's best efforts, in carefree 'chicken pox party' days (I'm old), while all of us got chicken pox, I never got mumps from my siblings and the sibling who got measles never passed it on to the rest of us. Not at all clear why I got off most lightly, especially because in a general way i was by far the 'sickliest' and would be the only one of us to have what is now described as 'an underlying health condition'.

dd1 had covid. We all isolated together and no one else got it.

Dd2 then went on to catch it a couple of months later despite not catching it from her sister, no one else in the house got it from her either.

Me, dh and 7 dc in our bubble.. 2 double vaccinated, 2 had 1 jab. Rest under 16.
1 double vaccinated caught it.
1 single..
3 dc.
Missed dh and 3 x dc .. Very odd.

Same as with any other illness - depends on multiple factors.

Like someone said upthread about chickenpox, I remember distinctly being dragged to the house of every child with chickenpox that my mother knew of as she said it would be worse to get it when I was older. I didn't catch it, not even when one of my younger brothers had it. But at 15, about to sit mock GCSEs, what did I catch, from an unknown source? Fucking chickenpox. Bizarre.

Anyway. Viral load, existing immunity from previous infections, vaccine status, length of exposure, general health, innate susceptibility... All will play a part.

Yea I was wondering what those factors were. I suppose if we knew exactly what they were, we would be in a different position with this virus altogether huh

Well I guess the factors are as suggested...

Viral load, existing immunity from previous infections, vaccine status, length of exposure, general health, innate susceptibility... plus probably more that we don't even know about yet.

Fascinating thread 🤔.

Pre existing t cell immunity is my theory. When Sars was being researched they found immunity to it in blood samples taken years before it existed. They think it was likely due to previous exposure to similar viruses. Lots more research needed.

Also wonder about this. Our family Covid encounters as follows:

1st event
DS2 gets Covid as close contact at school
Me double vax looked after her when she was ill but did not get it
DH just had 2nd vax did not get it
DD1 no vax
No one else in the house gets it

Now
DH - double vax has Covid from contact with another double vax person at work
Me - symptoms but negative PCR and LFTs so far 🤞
DD1 & DS - not vaccinated yet and hopefully will not get it, negative tests so far

So DH gets Covid when fully vaccinated from contact with someone at work yet didn't get it from someone in the same household when he had just one jab 🤷‍♀️

@Toty I've heard of that T cell theory as well. I guess we don't know exactly yet, but have some idea what may contribute to immunity . So I end up wondering.. if a vaccinated person does not pick it up, could that mean they also wouldn't have got sick / or had mild illness pre vaccination. There is no way of knowing that of course.

@SilverGlitterBaubles that's also weird. Maybe a different variant then ? No explanation. But even then, doesn't make much sense.

The reality is that no one knows yet. There’s a great Twitter thread from John Burns-Murdoch today considering the various evidence and theories.

*@strugglingmummy2021

Personally I think so. IF pre existing t cell immunity is an important factor then I don't think vaccination status would make a difference. Would love to see a large study done, it would be really interesting to see the results. We would have to test stored blood though since most people have either been vaccinated or exposed now.

DS had it (probably slightly pre the alpha variant). His friend isolated with him partly in the hope of getting it out of the way (mad, imho!). He didn't catch it from DS but did catch it a month later & doesn't know where from. By then alpha was the main variant which I guess was more infectious.

I worked on ICU through covid. Was exposed to a patient who falsely tested negative, high flow oxygen on 60 ltrs. I was wearing a normal surgical mask, fiddled with his nasal specs, he coughed frequently, I was in very close contact and didn't catch it.
5 months later I caught it off dp. He did have a high viral load as per test and trace. I was pretty sick for a good 6 weeks whereas he recovered far more quickly (although still had a cough for a few months). I seem to be the only one at work who has long covid although a friend has had random odd symptoms since she was infected (bad UTI, tiredness). At this point I wasn't vaccinated. I do wonder why I have been affected more than colleagues who on the surface have more risk factors ie obesity, age, poor fitness, smokers.

Good questions OP, I hope the scientists are asking them too!

I currently have Covid and I've had one vaccine. I have antibodies from the vaccine as I'm doing an antibody study for ONS and I got the results back. Still caught Covid.

Variations in immunity but also variations in opportunity. So people socialise more, or work in busier environments, or go to festivals...

A friend of mine is a senior midwife in the largest unit in the west of Scotland and is immunocompromised (RA, shitloads of drugs to maintain etc) and worked in v close proximity to patients since the beginning.

She's never had covid (and, obviously, being frontline NHS, has been tested regularly throughout).

Bizarre, innit?

Blood group also plays a part apparently. It seems to be group A more likely to catch Covid as per this article from March 2021

b-s-h.org.uk/about-us/news/growing-association-between-blood-group-a-and-covid-19/

I suspect there are a whole lot of scientific explanations as well as a big dose of "luck" in there too.

I know people who worked on the frontline throughout and never once tested positive. I also know if people who only ever went to the supermarket or other essential places and ended up catching it.

I've never had symptoms (apart from at the beginning of lockdown one) and neither has DH. We've never needed to test or isolate either.