People are rightly confused how is it that we have another wave when 60% or more are vaccinated, & 40-50% of the population has probably had COVID.
Where is immunity?


1/ How strong and durable immunity is following infection or vaccination depends on many factors.
2/ The strength and durability of the immune response depends on the nature of the antigen, how it is presented to the immune system, number of exposures, etc.

3/ With Covid we also got a bad deal: A new serious virus that we were not immune to, that spreads easily, & mutates.
4/ The immune response is more durable with repeated exposure: generation of a true secondary immune response.…

With natural infection sometimes one infection is long enough to trigger a durable secondary response. Sometimes its not, & you are susceptible.
5/ With any vaccine, the reason we space doses at least 3-4 weeks apart is to generate primary & secondary response. Either that spacing was too close for COVID vaccines, or due to the nature of antigen itself, 2 doses may not be enough for durable response: thus need for booster
6/ But 2 doses still remain highly effective in reducing risk of severe disease by >90%. Boosters will improve efficacy further.
7/ The fact that infections however mild can occur after 2 doses or prior infection can adversely affect vulnerable immunocompromised who are not as immune despite prior infection or vaccines. This is critical to remember. These are your loved ones.
8/ The virus mutating also means whatever immunity was strong against wild type or alpha, is not enough against delta.

9/ Viral exposure dose also matters. A huge viral dose exposure (as can happen in indoor crowded unmasked settings) can overwhelm the immune system.
10/ The other factor is with large populations, even 2 years into a pandemic, a huge number are probably still completely naive to the antigen: they have still never seen the virus or the vaccine. Probably ~40-50 million in the US.

With community spread, they get infection.
11/ Whether the booster provides a proper second exposure to the antigen and thus generates a long enduring secondary immune response, only time will tell.

I hope it does. We need to catch a break.
12/ If the virus mutates significantly then it spoils that plan. So getting vaccines to parts of the world that don't have vaccine is not only the right thing to do but in everyone's self interest as well.
13/ If the way the vaccines present the antigen or just the nature of corona viruses intrinsically doesn't elicit a decades long immunity against infection despite a booster, we many need annual boosters. We have to be prepared.
14/ Simultaneously monoclonal antibodies and oral drugs that reduce risk of severe disease will help.
15/ The positive message is that vaccines remain highly effective in reducing the risk of severe disease and deaths by >90%. The safest way to be is whether you have had prior Covid or not to get vaccinated, and get a booster if it's offered for you in your country.
This Table is from textbook Vaccines. @DrPaulOffit

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More from @VincentRK

21 Nov
Just like anti vaccine folks found Gibraltar, another place they keep pointing to is Vermont, the most highly vaccinated state.

Best for people know the facts.

1) No state has done as well as Vermont in this pandemic: fewest lives lost. They know what they are doing.
2) Vermont is the best vaccinated state and vaccinations have kept deaths low. Since June 1 by which data everyone had an opportunity to be vaccinated, deaths have continued to stay low in Vermont. But have increased in many less well vaccinated states.
3) Even Vermont is not as well vaccinated as it should be. So 72% while #1 in the US is lower than many countries. There are vulnerable people and unvaccinated people, so with delta cases will occur.
Read 9 tweets
21 Nov
Michigan COVID cases go higher than ever before. Only 54% in the state are fully vaccinated.
There are like 17 states with vaccination rates lower than Michigan.

Thanksgiving, Holiday season, and Winter are coming.
First things first. Get vaccinated if you haven't already. Get a booster if you are already fully vaccinated.

Vaccines prevent hospitalizations. A big deal in many ways, including because there are people with other illness who need beds.

Vaccines save lives.
Read 5 tweets
20 Nov
US has lost more lives to COVID in 2021 than 2020. But 450,000 deaths were prior to Feb 1, before any effect of vaccines could have occurred.

180,000 deaths since June 1, the date by which adults in USA could have been fully vaccinated if they wanted.…
The 100,000 lives lost in last 2 months is the most distressing. Because 90% of these were preventable.
For a while there till September things seemed to be going well. Hard to watch.
Read 4 tweets
20 Nov
In every age group, COVID vaccines reduce the risk of severe disease or death by >90%.…
Texas. H/T @ArielCohen37
Overall for the US. Age 65+…
Read 9 tweets
19 Nov
Suddenly a lot of anti vaccine have found Gibraltar.

My response:
1) While a breakthrough wave is occurring, the ~100% vaccine rate is keeping COVID deaths at zero or near zero.

2) "Natural immunity" from higher infection rate compared to US didn't prevent present wave either. ImageImage

1) 2 dose vaccine works really well in preventing deaths & serious disease.

2) We have vulnerable among us: elderly & immunocompromised, children less than 5 who cannot be vaccinated; and risks of long term Covid. So get a booster if offered.

3) Continue precautions
So instead of worrying about Gibraltar, or Malta, or Iceland, or Singapore or anyone else who has high vaccination rates — please get vaccinated if you haven't already done so.
Read 4 tweets
19 Nov
Breaking: As I anticipated, FDA approves boosters for all adults. With cases rising this is the right decision. Boosters are highly effective. Please get the booster shot — it will help mitigate a big Holiday wave.…
While we are concerned about vaccine equity and rise of vaccine resistant mutants elsewhere, time is of the essence in controlling rise in cases in the US.

Boosters are highly effective based on real world (Israel, UK) and RCT data. No question. 👇
This trend is in the wrong direction. Worrisome given winter and Holiday season.

-Boosters will help, but we also need 3 more things:

1) More unvaccinated need to be vaccinated
2) Masks, ventilation, limit crowding indoors
3) Increased use of rapid tests for indoor gatherings Image
Read 6 tweets

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