There is currently a resurgence of COVID-19 in Manaus, Brazil, despite the fact that about 76% of the population had been previously infected with SARS-CoV-2, which would normally lead to herd immunity. What is the cause of this resurgence? Short Thread. (1/n)
The truth is, nobody knows, but there are at least four mutually exclusive possibilities: (2/n)
1) The attack rate could have been overestimated during the first wave, meaning that the population remained below herd immunity. Attack rate is the percentage of an at-risk population that contracts the disease during a specified time interval. (3/n)
2) Antibody immunity might have waned by December, although this seems unlikely, because even if antibody levels fall, memory B cells endure much longer.

3) The currently circulating variants might evade immunity to previous variants. (4/5)
4) The currently circulating variants might be more transmissible than than previous variants.

In my humble opinion, I think possibility #1 is the most likely. (end)

thelancet.com/journals/lance…

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More from @GertrudRey

20 Feb
As more and more people are vaccinated, one of the major questions is whether or not the vaccines protect only from disease, or both from disease and infection. Short thread. (1/n)
Even if they completely prevent disease in a vaccinated person, there is a chance that that person can still become infected, replicate virus to a certain extent, possibly to a sufficient level to infect another (unvaccinated) person. 2/n)
The studies analyzing this feature of SARS-CoV-2 immunity are well under way. Here are results from one such study from Israel, which is ahead of the rest of the world in the vaccination process. (3/n)

medrxiv.org/content/10.110…
Read 5 tweets
7 Feb
Vaccines, convalescent plasma, and monoclonal antibodies.

What is the difference between these three things and what do they have in common? A thread. (1/n)
The major shared feature is that they all involve the action of antibodies, but the source of the antibodies and their durability is vastly different. (2/n)
Vaccines present or lead to the presentation of an antigen (e.g., a piece of a virus) that induces your immune system to make your own antibodies. Those antibodies stay in your body for a long time and are affiliated with an immune memory that lasts even longer. (3/n)
Read 12 tweets
7 Jan
What is in your mRNA vaccines and why could they be made so quickly? A thread, also at virology blog. (1/n)

virology.ws/2021/01/07/rna…
It is now a little more than a year since the emergence of SARS-CoV-2, and we already have several highly effective vaccines against this virus. (2/n)
Because of my previous research experience in vaccine science, I was very skeptical about the promise of a SARS-CoV-2 vaccine this soon. I was wrong, and I could not be happier about that. (3/n)
Read 32 tweets
20 Dec 20
What are bioRxiv and medRxiv? They are servers where anybody can self-publish a scientific article. Legitimate journals put a submitted research paper through pretty rigorous peer review, but the publications on these "preprint" servers are not peer reviewed. Thread. (1/n)
As you might imagine there can be quite a bit of junk on there, including the paper that has been making headlines, allegedly showing that SARS-CoV-2 RNA can be reverse transcribed and integrated into the human genome. (2/n)
The conditions under which these experiments were done were extremely artificial, where probably just about any RNA would have been reverse transcribed and integrated. But the authors didn't show that. (3/n)
Read 5 tweets
25 Nov 20
Several people have expressed concern over the Pfizer/Moderna vaccines because of their mRNA composition and the alleged possibility that this mRNA could integrate into our DNA and remain in our DNA forever (kind of like HIV does). Short threat about why this can't happen. (1/n)
I attach a graphic that illustrates the central genetic dogma. Generally, our human DNA is transcribed into RNA (red arrow), which is then translated into protein (green arrow). (2/n)
HIV is an RNA virus that goes against this dogma and is “reverse transcribed” into DNA in the cytoplasm of our cells after it enters our cells, using an enzyme called “reverse transcriptase” (straight yellow arrow). (3/n)
Read 9 tweets
23 Nov 20
Most people think of clinical trials as consisting of Phases I-III, but did you know that there is also a Phase IV trial? Short thread. (1/4)
Phase IV of a clinical trial is also known as a postmarketing surveillance trial and involves the continued surveillance of a drug or vaccine's safety. (2/4)
This trial continues indefinitely and it is the reason why I am such a strong advocate for vaccines. The safety and efficacy of vaccines is one of the most highly scrutinized premises in biomedical science. (3/4)
Read 4 tweets

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