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?
Thread.
1/ How strong and durable immunity is following infection or vaccination depends on many factors.
Where is immunity?
Thread.
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.
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. microbiologynotes.com/differences-be…
With natural infection sometimes one infection is long enough to trigger a durable secondary response. Sometimes its not, & you are susceptible.
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.
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.
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.
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.
https://twitter.com/vincentrk/status/1462079514540974088
This Table is from textbook Vaccines. @DrPaulOffit
Related thread on immune response.
https://twitter.com/VincentRK/status/1447967441380859908
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