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Céline Gounder, MD, ScM, FIDSA Profile picture
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31 Jul, 6 tweets, 2 min read
1) The COVID vaccines are highly SAFE and EFFECTIVE.
- Over 4 billion doses have been administered worldwide.
- Over 350 million doses have been administered in the U.S.
- They are highly effective in preventing severe disease, hospitalization, and death from COVID.
2) BREAKTHROUGH INFECTIONS appear to be EXCEEDINGLY RARE, at least pre-Delta.

(We're still learning about the Delta variant.)
3) BREAKTHROUGH INFECTIONS typically cause no symptoms or minimal symptoms.

We see very little BREAKTHROUGH DISEASE, where people have low oxygen levels, end up in the hospital, or end up dead from COVID if they've been vaccinated.

theatlantic.com/science/archiv…
4) This week we learned that those exceedingly rare cases of BREAKTHROUGH INFECTION can be CONTAGIOUS.

5) Though an INDIVIDUAL with a breakthrough infection may be highly contagious,

the risk of a breakthrough infection is exceedingly low,

so the degree to which vaccinated people contribute to community transmission is exceedingly low.
6)
POPULATION ATTRIBUTABLE RISK = % SARS-CoV-2 transmission by UNVACCINATED vs VACCINATED

UNVACCINATED PERSONS ARE RESPONSIBLE FOR MOST TRANSMISSION OF SARS-CoV-2.

So yes, @BenWakana46 is right.

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More from @celinegounder

Céline Gounder, MD, ScM, FIDSA Profile picture
30 Jul
1/ Here’s the CDC MMWR’s report on the cluster of vaccine breakthrough infections in Provincetown.

I started hearing about these infections from friends in mid-July.

THIS is the report that led the @CDCgov @CDCDirector to issue new guidance on masking.

cdc.gov/mmwr/volumes/7…
2/
469 SARS-CoV-2 infections

346 (74%) were among fully vaccinated

Of these:
16% J&J, 46% Pfizer, 38% Moderna
3/
Among virus samples that were genetically sequenced, 90% Delta variant.

80% of vaccinated persons with breakthrough infection had symptoms like cough, headache, sore throat, muscle aches, and fever.
Read 6 tweets
Céline Gounder, MD, ScM, FIDSA Profile picture
29 Jul
1/ This latest paper by @KizzyPhD, who helped develop @moderna_tx's mRNA COVID vaccine, helps us understand why vaccines can protect against severe disease in the lungs but not mild infection in the nose and throat.
science.sciencemag.org/content/early/…
2/ Lower antibody levels are needed for reduction of viral replication in the lower airway than in the upper airway.

RNA in BAL = amount of virus in the lungs drops more quickly than
RNA nasal swabs (NS) = amount of virus in the upper airway
3/ Antibodies taken from unvaccinated & vaccinated non-human primates (NHPs) were infused into hamsters.

Hamsters that were given antibodies from NHP who received the higher dose vaccine had little/no weight loss (i.e. little/no disease).
Read 5 tweets
Céline Gounder, MD, ScM, FIDSA Profile picture
28 Jul
1/ Today, Pfizer released a PRE-PRINT with 6 months of follow-up data for its phase 2/3 COVID vaccine trial:
medrxiv.org/content/10.110…

THE TAKEAWAY: 2 doses of the Pfizer vaccine are highly effective in preventing severe disease, hospitalization, & death out to 6 months.
2/ Pfizer saw no new safety issues between its 2-month and 6-month analyses.

This is consistent with what we've seen with every other vaccine. If people are going to have a side-effect from a vaccine, they'll have it within 2 months of getting vaccinated.
3/ The Pfizer vaccine was over highly effective in preventing ANY SYMPTOMATIC INFECTION out to 6 months:
2 months 96%
2-4 months 90%
4-6 months 84%
Read 4 tweets
Céline Gounder, MD, ScM, FIDSA Profile picture
28 Jul
1/ Pfizer says that a 3rd dose of its vaccine can boost protection against the Beta & Delta variants
BUT
does everyone need that boost?
2/ Do severely immunosuppressed people need extra doses of COVID vaccine? Certainly.
3/ Do older people (esp over 80) need extra doses of COVID vaccine? Probably.
Read 4 tweets
Céline Gounder, MD, ScM, FIDSA Profile picture
27 Jul
1/ How is it possible that vaccines could prevent severe disease, hospitalizations, & deaths from COVID

BUT not prevent mild infections & onward transmission?

advances.sciencemag.org/content/7/12/e…
2/ If the vaccines induce systemic immunity protecting the lungs

but not mucosal immunity in the upper airway (nose, throat),

you could still get upper airway SARS-CoV-2 infection, causing no or mild symptoms

without severe illness (e.g. hypoxia or low oxygen levels).
3/ We're already seeing the benefit of mixing-matching different types of vaccines (what we call heterologous prime-boost).

Perhaps we should be doing the same with injectable COVID vaccines and intranasal COVID vaccines.
Read 4 tweets
Céline Gounder, MD, ScM, FIDSA Profile picture
27 Jul
1/ Clearing up confusion about what it means that Delta viral loads are ~1000x higher than the viral loads seen with the original SARS-CoV-2.
medpagetoday.com/special-report…
2/ We need to be precise in speaking about infectiousness.
Exposure = Dose x Time
If viral loads in infected people are ~1000x higher with Delta than original SARS-CoV-2, the dose of virus to which the uninfected person is exposed has gone up ~1000x.
3/ Exposure = Dose x Time
If Dose increases 1000x
the Exposure you would have gotten from an infected person early in the pandemic over 15 minutes
you now get in 0.9 seconds (~1 second).
15 minutes = 900 seconds
But in NEITHER scenario are you 100% sure to be infected.
Read 7 tweets

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