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Sabina Vohra-Miller Profile picture
@SabiVM
May 8, 2024 • 7 tweets • 3 min read • Read on X
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New post on Rapid Antigen Tests. Will post the entire thread here instead of just a link, given importance.

A master thread with current data: key concepts, which brands are more sensitive, tips to improve sensitivity & important considerations. 1/7 RAPID ANTIGEN TESTS A master thread with current data: key concepts, which brands are more sensitive, tips to improve sensitivity and important considerations.
Recent CDC MMRW Report found overall sensitivity of RATs was 47% compared to PCR.
The peak percentage of positive RAT was 59.0% occurred 3 days after onset of symptoms.
Highest on days when fever was reported, lowest on days when no symptoms were reported. 2/7 RAPID ANTIGEN TESTS - OVERALL SENSITIVITY Recent CDC MMRW Report assessed the performance of Rapid Antigen Tests (RATs) compared to PCR. The study collected data from a household transmission study between Nov 2022 - May 2023. Overall sensitivity of RATs was 47% compared to PCR. The peak percentage of positive RAT was 59.0% and PCR was 83.0%, which occurred 3 days after onset of symptoms. Highest sensitivity for RATs was on days when fever was reported, and the lowest sensitivity was on days when no symptoms were reported.
Overall QuickVue and Flowflex had the highest sensitivity. Special mention for Australian Fanttest. Several commonly used RATs performed extremely poorly.
3/7 CERTAIN BRANDS ARE MORE SENSITIVE Several studies on Omicron-related variants have been conducted to assess the sensitivity of various brands of RATs Overall QuickVue and Flowflex had the highest sensitivity. Special mention for Australian Fanttest. A new study just published looked at 10 commonly found RATs in Canada. Of these, the three that were best performing wer that were best performing were: BTNX Cassette (spit) Flowflex Medsup The worst performers were: BTNX, PCL, PanBio, SDBiosensor, StandardO A US-based study looking at common US tests found the following sensitivity: Health 73...
One study showed RAT accuracy increased from 38% to 92% with repeat testing.
A single negative RAT test cannot rule out infection.
Current guidance suggests to repeat the test 48 hours after the first negative test & potentially a 3rd time if you still have symptoms. 4/7 TESTING MORE OFTEN IMPROVES ACCURACY Studies show that repeated rapid antigen tests increase accuracy drastically One study showed RAT accuracy increased from 38% to 92% with repeat testing. A single negative RAT test cannot rule out infection. Current guidance suggests to repeat the test 48 hours after the first negative test and potentially a third time 48 hours after the second test if you still have symptoms.
Including an oral sample along with a nasal sample on the same swab can increase test sensitivity.
5/7 ORAL AND NASAL TOGETHER CAN IMPROVE SENSITIVITY Including an oral sample along with a nasal sample on the same swab can increase test sensitivity. To do this: 1- Do not eat or drink for at least 30 minutes before collecting the oral sample. 2- Insert the swab between both inner mouth cheeks and lower gums and turn the swab around a few times. 3- Then rub the swab on your tongue as far back in your throat. You can also swab the back of your throat and tonsils. 4- Then using the same swab, insert it straight back into your nose and rotate the swab for a few seconds. Repeat in the second nostr...
If you are elderly, at higher risk, eligible for anti-virals such as Paxlovid, PCR tests are recommended.
If your RAT is positive, you continue to be infectious.
To know when to stop isolating or masking, two consecutive -ve RATs 24 hours apart (after a +ve RAT). 6/7 GENERAL CONSIDERATIONS If you are elderly, immunocompromised or at higher risk for severe disease, or eligible for anti-virals such as Paxlovid: PCR tests are recommended for you so that it doesn't delay you obtaining appropriate care and treatment. However, PCRs tests are getting harder to find and more inaccessible, which is frustrating. If your RAT is positive, you continue to be infectious. PCR tests can remain positive for up to 3 months after an infection, since they pick up all viral remnants, including dead and inactive virus and also involves an amplification step to make it more s...
A post on key concepts and considerations 7/7 Key concepts on COVID-19 Rapid Antigen Tests (RATs) RATs are an important tool; however, PCR tests are the gold-standard RATs offer a snapshot of at a specific time and place Think of it like a polaroid picture. It only offers a glimpse of what the situation is at that current time. Do a RAT just before attending an event If you're attending a family gathering in the evening, consider doing a RAT in the morning, and then another one just before you leave the house to attend the gathering. If your RAT is positive, does it mean you are infectious? YES! RATs only test for active viral nuc...

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More from @SabiVM

Sabina Vohra-Miller Profile picture
Jan 12
A new longitudinal cohort study found that children who were sick more often in early childhood were more likely to continue being sick in later childhood with more moderate to severe infections and require more antibiotic therapies. /1 Early childhood infections do NOT strengthen your immune system...they only make you sicker throughout childhood. Data from a new study
/2 This was a longitudinal cohort study of children from birth to age 10-13 years from the Danish population-based birth cohort between November 2008-2010. Children were monitored for infection diagnoses and antibiotic prescriptions until February 1, 2024, by when they were aged 10- or 13-years. Children with immune deficiencies or congenital diseases were excluded. Additionally, an extensive list of confounders/biases including social and environmental risk factors were take into consideration and included in the analysis. A total of 614 children from birth to 3 years had completed follow...
/3 Children with a high burden (≥16 episodes) of diary-registered infections between birth and 3 years had an increased risk of later moderate to severe infections as well as antibiotic treatments until age 10 or 13 years. Each diary infection episode also increased the later risk of moderate to severe infections and antibiotic treatments. Subtype analyses showed significant associations between each cold, acute otitis media (ear infection), pneumonia, gastroenteritis (stomach flu), and fever episode between birth and 3 years and risk of later moderate to severe infections or antibiotic t...
Read 5 tweets
Sabina Vohra-Miller Profile picture
Aug 27, 2024
Canada specific FAQs on the updated Covid-19 vaccines
🧵 1/8 Image
Options available:
Pfizer and Moderna: both of these will target the KP.2 variant.

The mRNA vaccines are anticipated to be available around the middle of October.

Unfortunately Canada did NOT purchase any Novavax for 2024-2025.
2/8 Options available in canada Health Canada has received submissions from both Pfizer and Moderna for the updated COVID-19 vaccines. Both of these will target the KP.2 variant. The mRNA vaccines are anticipated to be available around the middle of October. Currently, KP.3.1.1 is the dominant COVID-19 variant, overtaking parent linage of KP.3 and KP.2 variants. Unfortunately Canada did NOT purchase any Novavax for 2024-2025. This is partially because of lower uptake of this vaccine, and also because Novavax had already committed to vaccines targeted towards the JN.1 variant (predecessor of...
NACI Recommendations
An updated 2024-2025 COVID-19 vaccine should be offered as a strong recommendation to:

- All adults 65 years of age or older
- Those 6 months of age and older at higher risk of exposure or illness.
3/8 NACI Recommendations An updated 2024-2025 COVID-19 vaccine should be offered as a strong recommendation to: All adults 65 years of age or older Those 6 months of age and older: Residents of long-term care homes and other congregate living settings Have underlying medical conditions that place them at higher risk of severe COVID-19 Who are pregnant In or from First Nations, Métis and Inuit communities Members of racialized and other equity-deserving communities People who provide essential community services
Read 8 tweets
Sabina Vohra-Miller Profile picture
Jul 22, 2024
We are in a summer COVID surge and this has lead to many questions! In this post @LizMarnik and I share things to consider to protect yourself, what we both do & consider in our own actions and recommendations for others to help make society safe & equitable for all.
🧵 1/8 WE ARE IN A COVID SURGE. WHAT THINGS SHOULD YOU CONSIDER?
Why are cases increasing? Mostly due to new variants, summer behaviours such as travel and really, because that’s just how pandemics work.
2/8 Why are cases increasing? 1. New variants: KP.2 and KP.3 make up a large percentage of the COVID-19 cases right now. These are two new variants that have differences compared to prior variants. This means that prior infection and vaccination doesn't give as much protection for these newer variants. Fall vaccines will target JN.1 (Novavax) or KP.2 (mRNA) but these are not yet available. 2. Summer behaviors: As the weather warms, people move indoors to air conditioned indoor settings. Summer also brings with it things like large parties and gatherings, new settings for children like camps and...
There are lots of things you can do to stay safe:

Mask, esp indoors. Test. Be in well-ventilated areas, outdoors preferred, stay home when sick and vaccinate.
3/8 How to stay safe during a surge? Mask: Especially when indoors and in crowded areas. Wear a well-fitted respirator. Test: Keep tests on hand for when you have symptoms. Remember while it is allergy season for many, symptoms can overlap with viral infections. Be in well-ventilated areas: Choose outdoors over indoors. Open windows, run HEPA filters & use CO2 monitors indoors. Higher CO2 means there is not as much ventilation therefore risk is higher. Eat outdoors: Choose a restaurant patio, a picnic at a park or if your kid goes to camp, request they be able to eat lunch outside Keep your ger...
Read 8 tweets
Sabina Vohra-Miller Profile picture
May 9, 2024
So much disinformation on AstraZeneca's announcement re: withdrawing their COVID-19 vaccine, so I thought I should go back and review the timelines of what occurred in Canada.

Hang on, because this is going to be a wild ride. Thread, and a long one. /1
theguardian.com/business/artic…
Image
AstraZeneca's COVID-19 vaccine was first approved in Canada on Feb. 26, 2021. /2
cbc.ca/news/politics/…
Image
In Canada, it was first only recommended to be used in adults 64 and younger. This is because the initial study results were too limited to allow a reliable estimate of vaccine efficacy in individuals 65+. /3
ctvnews.ca/health/coronav…
Image
Read 24 tweets
Sabina Vohra-Miller Profile picture
Apr 25, 2024
Avian Flu:
Current situation, context and what you need to know 1/8 Image
AVIAN FLU - A BRIEF HISTORY:
Highly Pathogenic Avian Influenza (HPAI) is caused by Influenza A H5 and H7 viruses. The current highly infectious strain of Avian Influenza that is spreading is the H5N1.
H5N1 is not new. 2/8 AVIAN FLU - A BRIEF HISTORY: Highly Pathogenic Avian Influenza (HPAI) is caused by Influenza A H5 and H7 viruses. The current highly infectious strain of Avian Influenza that is spreading is the H5N1. H5N1 is not new. It was first detected in chickens in Scotland in 1959; however that strain was very different from the current version of H5N1 which underwent a significant evolution around 1997. Sporadic cases and outbreaks have resulted in hundreds of human cases of the H5 Avian influenza virus, particularly the H5N1 subtype and predominantly from direct contact with infected birds in comme...
Currently we have an outbreak of the subtype H5N1 clade 2.3.4.4b.
There are 33 outbreaks across 8 states in cattle reported in USA. None in dairy cattle in Canada, CFIA monitoring closely.
This degree of spread outside of birds & poultry is unprecedented & concerning.
3/8 Currently we have an outbreak of the subtype H5N1 clade 2.3.4.4b. There is some data to show that this strain requires a lot more direct contact for spread to humans than H7N9. Avian flu has been spreading amongst wild birds, poultry and as of recently, dairy cattle. It is now estimated that it has been spreading in dairy cattle since late 2023. As of April 21st, there are 33 outbreaks across 8 states in cattle reported in the USA alone. Avian flu has not yet been discovered in dairy cattle or other livestock in Canada; however, CFIA is currently on high-alert and monitoring closely. In add...
Read 10 tweets
Sabina Vohra-Miller Profile picture
Apr 2, 2024
In science & esp medicine, risk is a tricky thing to contend with - besides of course being a mathematical one - and involves many considerations in order to have a more fulsome understanding.

In this post @LizMarnik and I attempt to explain these concepts. 1/9 Let’s talk risk What is relative vs absolute risk? What is cumulative risk? Why do these terms matter? And how do these impact our lives?
In simple terms, risk is the probability of an event occurring. In statistical terms, the risk of an event occurring is simply defined as its probability.
2/9 WHAT IS RISK? In simple terms, risk is the probability of an event occurring. In statistical terms, the risk of an event occurring is simply defined as its probability. Absolute risk of a disease is your risk of developing the disease over a time period. Relative risk is used to compare the risk in two different groups of people. What does this mean?
Take a fictitious disease - AhCrap. Risk of dying due to this is 2/million & using GoodStuff tx can reduce risk to 1/million.
While relative risk reduction is 50%, only one less person out of 1M w AhCrap are saved by GoodStuff, making absolute risk reduction fairly small.
3/9 ABSOLUTE VS RELATIVE RISK Take a fictitious disease, say Disease AhCrap. The risk of dying due to AhCrap is two in a million - ie, for every one million people who suffer from AhCrap and are not treated, two out of these one million people will die. Let's say we have a way to treat this AhCrap disease, using GoodStuff treatment. This treatment can reduce the risk of dying from two in a million to one in a million. Because the risk of dying decreased from two in a million to one in a million, the relative risk decreased by 50%. However, the absolute risk only changed from 2/1,000,000 to 1/1,...
Read 9 tweets

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