Thread by @RajeevJayadevan

Why vaccine passports are invalid.

This thread in response to query by @FaruquiNeha based on an article by @Craig_A_Spencer that essentially states vaccinated people are less likely to be infected.

While that statement is true, it doesn’t address the whole issue.👇

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https://twitter.com/faruquineha/status/1442319608833196035

I will address the key question here with an example.

You are in a room with ten other people.

You want to know if it is safe; and whether any of them could pass the virus on to you.

The basic concept of vaccine passport is that such a person will not give you the virus.

2/

But in reality, we can no longer classify everything in binary terms (black or white)

According to the proponents of vaccine passport, only two kinds of people exist in the universe.

The vaccinated, and the unvaccinated.

Unfortunately, that is not the reality. 👇

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The room has not 2, but at least 10 categories of people.

1. Fully vaccinated, recent
2. Fully vaccinated, remote (more risk)
2. One past infection, recent
3. One dose vaccinated plus past infection
4. One dose vaccinated, but no past infection
5. Two (or 3) past infections

4/

6. No past infection, no vaccination, but extremely careful person.
7. Fully vaccinated but active socialite, not good at mask wearing
8. Past infection, very careful person
9. Unvaccinated, socialite, never wears masks
10. Person (any status) who keeps quiet, wears a mask

5/

These 10 (and more) categories of people each have different risks of:

1.bringing the virus into the room, and

2. Spreading it around in the room.

It is true that someone who had been fully vaccinated (recently, within 2 months) is very unlikely to be carrying the virus.

6/

In the first two months it is almost impossible to get infected, or to spread infection. But in real life, in a public place, how likely is it to encounter such a person?

Each of the ten categories of people I listed above have different risks for the two variables above.

7/

A person transmits most virus in the first 4 days, starting from the days prior to onset of symptoms when viral load is max.

Whether they are vaccinated or not, this viral load remains the same, among those who are infected.

8/

While it is shown that viral load drops in the last few days in the vaccinated, it doesn’t really matter because spread mainly occurs in the beginning, not the end.

And this occurs when the person least suspects to be infected, which is particularly true among the vaccinated.
9/

It is true that in those who had been fully vaccinated, the odds of infection are lower, but that also depends on:

1. How long it’s been since vaccination

2. What is the person’s overall social behaviour & compliance with pandemic precautions, (which we have no control of)

9/

Now let’s look at the other 8 categories.

Without elaborating on each, it is clear that each of these people are in varying shades of gray, and not in black or white categories.

Past infection protects against reinfection much the same way as vaccination, see below 👇

10/

Long thread, please see the whole thread for context. Also see above ☝️

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https://twitter.com/RajeevJayadevan/status/1431462104553320450

And then there are past infected people who have received one dose, or two doses. This is called hybrid immunity. That is also very good protection.

If we continue to divide people into textbook style black and white (good and bad) categories, we are being blind to science.

13/

Serosurveys have shown high prevalence of antibodies in populations, which indicate that a large number of people are already past-infected category.

This cannot be ignored any longer while discussing “vaccine passport”

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Unfortunately it is not easy to document past infections, as

1. half the cases were without symptoms, and

2. total antibody level drops off after 3 months.

(A small baseline level will remain which can’t be picked up by routine assays)

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In summary, we can’t look at the ten people in the room and classify them as “good or bad”, “safe or unsafe” - any longer.

It is definitely a good idea to vaccinate people because that is the most definitive and safe method of reducing the risk of severe disease and death.

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But that should not mean that those 9 other people should be thrown out of the room, simply because they “don’t fit” the black and white category of “vaccine passport”.

Some ideas are bad, and it is not worth hanging on to them.

We need to move on.

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