Confused by household transmission stats

[loveandroses]

I was having an argument with an anti-vaxxer friend. He told me that the household transmission rate is roughly 12%. I looked this up and sadly he appears to be right. I have attached an image which comes from twitter.com/kallmemeg/status/1451828458544369667?s=20 . (Sad because every time he is right about something he takes that as more evidence that he is right to be an anti-vaxxer). However, I am not sure I really understand what "household transmission rate" or "secondary attack rate means".

Does this mean that if one person gets covid and lives in a house with 3 others, say, then there is only a 1 in 8 chance that any of the others in the house get covid? This sort of stats is not my strong point. My personal experience is that it is rare for only one person to be infected in a house so this 12% figure seems very surprising if it is really true.

Is your friend really anti vaccine or has he just decided not partake of covid vaccines?

I have no idea if those stats are correct but from my own personal experience it’s not rare for symptomatic covid cases to be confined to one family member, it happened in our house twice.

In the link what she says Delta is 12% more transmissible than the previous variant (which was Kent).

I don't think she actually mentions what % chance there is if someone transmitting it in a household.

"Household SAR: 12% (8%-16%) more transmissible"

Wow, anecdotal I know but 2 ds got it then within 2 days me, Dh dd and ds in law had all caught it ( dd and ds in law live in our annexe so not strictly in the same house. It's very very contagious indeed.

@Oldgoat2021 In the table I pasted there is a column "Secondary attack rates in household contacts". Isn't that it?

I've no idea what the rate is but Dh has confirmed Covid right now and I'm completely fine (we are being careful) - I've had a PCR test and I have no symptoms so no illness - yet

I don’t know how a rate like this is calculated, but if you have a hypothetical family of 5, and one person contracts covid outside the house. In a hypothetical scenario where they then give covid to everyone else in the house (100% transmission?), that means that no one else in the house can pass covid on to anyone else in the houses because they’ve already got it? So for them the rate would be 0%? Or do stats like this only look at the transmission from the first person in the house to get covid?

My point really is that unless you know what exactly is being measured and how, the stats don’t mean much.

@SickAndTiredAgain That is my problem exactly!

The problem with google is that you can find all sorts to back up your argument. The information won’t be put in the right context, you have to be diligent about sources and check the dates.

For example read this

Household transmission looks to be the most likely way to catch it. And logically that makes sense. One person brings it in, then spreads to another. Then that person plus the original can spread it to others in the house.

I think one weird thing about Covid is that you get large superspreader events, but actually a lot of people, possibly even the majority, don’t pass it on.

My dd confirmed pos on Mon 18. Five in household, all had neg PCR tests 19/20, me and DH now have it. Both DH and I are dble vac and this is the second time for me to get it. I have been wondering what the point of vaccination is if less than 6 months after fully vac I get it again.

@Iamtheweedonkey Re: vaccination point. Hopefully you are not too ill this time?

I’m really interested in this because we’re a family of 6 and one ds first got symptoms 8 days ago followed by a positive lateral flow then a positive pcr. All of us are still negative (daily lateral flow followed by a recommended pcr yesterday due to ds having it). I know it can take up to 14 days to catch it but I’m just surprised that in a family of 6 with 1 bathroom where 3 boys share a room I was thinking at least one child would have it (me and DH are double vacs). I’m pleased obviously just surprised as it’s such a contagious disease.

Family of 8 here, one child got it and none of us contracted it (neg LFTs and PCRs) .

my ds 10 got it at christmas no one else got it (3 of us), negative PCRs
ds 12 has it now we are on day 8 and so far no one has got it, multiple LFTS done and 2x PCRs

My DD had it and within 3 days everyone in the home also tested positive.

This study from early in the pandemic suggests a 1 in 6 chance of being infected from someone in the household.
“ We found that the risk of infection from exposure to a single infected household member aged ≥5 years (17.3%,13.7-21.7) was more than three-times that of extra-household exposures over the first pandemic wave (5.1%,4.5-5.8). Young children had a lower risk of infection from household members. Working-age adults had the highest extra-household infection risk. Seropositive asymptomatic household members had 69.4% lower odds (95%CrI,31.8-88.8%) of infecting another household member compared to those reporting symptoms, accounting for 14.5% (95%CrI, 7.2-22.7%) of all household infections.”

That was from Nature
www.nature.com/articles/s41467-021-23733-5

Having read the actual document it comes from, there's not really enough information there about how it's calculated to be able to interpret what it means.

That said, based on the info there it's likely to be an underestimate - poor quality samples excluded, relies on cases being reported to Track & Trace etc. Not necessarily a significant underestimate.

I guess the main takeaway from it for your anti-vaxxer friend would be that the data is from August and September, when most people will have been double jabbed. So not sure how they're surmising that the low secondary attack rate when most people are vaccinated supports their argument for not getting the vaccine.

More anecdote here. Just back from visiting my mum for a few days. While there my dB visited. Mum and dB tested positive on Wednesday, I got tested Friday - positive, and dp got a positive today. All double vaccinated.

It’s important to distinguish between earlier studies and more recent ones relating to the delta variant, which has a higher transmission rate.

It's taken two weeks for my partner to get it after my ds10 was positive.

Me and my other ds10 are still negative, we have done so many lateral flows and pcrs. I felt really unwell last week and was so surprised I was negative.

dh had it in August. Me and DD were both fine, never had symptoms, tested negative twice and an anti body test later confirmed I didn't have it. All unvaccinated btw

Myself, DH and 5y old have it just now. First time and also first time testing at all. Both of us have both vaccines. Oldest 13y seems negative on 3 laterals and has had his vaccine. Waiting on PCRs confirming, but laterals we're strong positives straight away.

Taken 2 weeks from 1st positive for whole whole house to test positive.