Someone in my house has coronavirus. How likely is it that I will get it?

Throughout the pandemic, one of the biggest risks of COVID has been sharing a home with an infectious person.

Given the prevalence of COVID, and especially the newer variants, you can imagine if you live with someone who has COVID, it is inevitable that you will become infected.

But this is not the case. A recent study suggests that you You have A 42.7% chance of contracting COVID from a housemate who tested positive for Omicron.

This means that if someone introduced an Omicron variant to a family of six, you would expect to infect two of the remaining five family members, on average.

How is transmission of infection measured at home?

We use the ‘secondary attack rate’ to describe the average number of secondary infections among a group of exposed people, once the virus has entered a particular environment such as a home. It represents a number of different factors including:

  • How contagious is the virus?
  • How high is the viral load of an infectious person, and how efficiently they release the virus
  • sensitivity of others present
  • Characteristics of the place such as crowding and ventilation.

The Secondary attack rate It is average, and transmission varies greatly between families. So some families see all of their members infected, while others have little or no transmission.

Since early in the pandemic, we’ve also seen “widespread”, with a small number of people responsible for a large proportion of new COVID cases.

On the other hand, a large proportion of patients Don’t post it at all.



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How has transmission changed within the family through the epidemic?

a dimensional analysis (Where results from previous studies are grouped together) Published in April, it combined results from 135 studies and 1.3 million people in 136 countries published in the Journal of the American Medical Association (JAMA).

She estimates that the secondary home attack rate of the original virus was 18.9%. So, your risk of contracting COVID if you share a home with one or more infected people was roughly one in five.

Some people don’t spread COVID at all.
Rex Becker / AAP

The increase in the infection of the new variants that emerged in late 2020 has translated into an increase in the transmission of infection at home. The alpha variant has a home secondary attack rate of 36.4%. This dropped to 29.7% for the delta variant, before rising again to 42.7% for the omicron.

However, even large and comprehensive studies like this are limited in their ability to make direct comparisons of all factors that may influence secondary attack rates, such as the home environment, behavior of household contacts and use of masks to name a few. Newer Omicron variants were not included in this study.

Why did the secondary attack rate on the family vary?

The secondary attack rate of the delta variable decreased compared to the alpha variant, despite the increasing infection. This is likely explained by the increased immunity in the population – whether due to vaccination or previous infection.

While the vaccines have not been as effective against Delta as previous variants, and the protection has diminished over time, they still reduce the risk of transmission in the home.



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Despite the significant increase in infection of variants Omicron and Immune escape propertiesHowever, the risk of infection at home is still only 42.7%. It is possible that the increased immunity of the population is the reason why it is not so high.

Vaccination reduces transmission of infection

The decrease in the rate of secondary home attacks was Larger When families received the booster vaccination.

The takeaway is that sharing a home with an infectious person does not mean that you will inevitably become infected, but a full vaccination helps reduce the spread of Omicron among household contacts.



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