Body takes repeat threat way more seriously. That's the reason second dose of vaccine mRNA creates about 10x more antibodies. Almost all kids vaccine require a second or even 3 shots with months of gap in between to create stronger immunity. (https://www.cdc.gov/vaccines/schedules/hcp/imz/child-adolesc...)
If you keep a tab on the news you might have seen antibody level from covid vaccines drops significantly over time. Actually same is true for people already have covid; natural protection wanes off within few months.
The bottom line is, it's that after second vaccination amount of antibodies start to decline and at some point of time efficiency of vaccination going down with it.
The "better" long term protection by longer gap between doses probably just buys extra couple of months or so of good efficiency at cost of lowered between two shots
Two (or more) doses are fairly standard for vaccines. The first to trigger seroconversion, the subsequent ones to exercise the secondary immune response (and for those relative few individuals who did not seroconvert after the first jab). The interval between them is typically quite long, often on the order of years [1]. From that pov, the 3-4 week booster interval for the COVID vaccines is tiny. It's likely the minimum possible interval given that seroconversion takes >= 14 days (I'd guess the short interval was chosen to get trial results as soon as possible). There are many reasons to think that alternative dosing schedules would be not only viable but better than the current default.
There are studies that show, that you do not have much protection against an infection half a year after your second dose. This is true for all available vaccines in the western world. You probably still have protection against a severe outcome, but not against getting infected and thus spreading the virus.
A third dose, even of the same stuff, will again increase your amount of antibodies and therefore lessen the chance of an infection in the first place. Using a different vaccine as third dose seems to offer even more protection.
One hypothesis I have seen around is that is not so much the time since the last shot, but the longer time span between shots that slows for more robust antibody response
Seems reasonable, as many of the booster doses for more established vaccines are spaced months to a year apart. There hasn’t really been enough time to study this comprehensively for the coronavirus vaccines
I have little understanding of this but someone who actually works on vaccines told me this theory: Your body upon coming in contact with the vaccine starts to product antibodies (the first shot). This is generally enough for a normal immune system to fight the disease if in the future the body was to come in contact with the virus. The second shot is for hyper immunity after 4 weeks. What it does is that it basically tells your body make a lot more antibodies now and the second shot is actually a booster shot. So every time you take a shot afterwards (like in the middle of a pandemic) your body produces an abundance of antibodies and will likely fend off the virus much more easily than if there was no booster dose of any kind and just a vaccine shot. This is important because simply protecting your body from the virus is not enough since you could be carrying the virus and spreading it with mild infection which will not be a problem for you but will not protect others and so the hyperimmunity is important for preventing spread during a wave. I won’t be surprised if this one is a yearly dose as you need to be hyperimmune to not show symptoms and spread.
The antibodies are not all that matters, they would simply disappear over time. The second dose spurs the B & T lymphocytes to produce even more.
> That booster shot is necessary for the T-cells to stimulate the memory B-cells to produce massive quantities of antibodies. If the booster isn’t given within the appropriate window, lower quantities of antibodies will be produced that may not provide as powerful protection from the virus.
Two doses is very common for vaccines because this is based upon how the immune system responds to real infections. The first dose will initiate a primary immune response. The second dose will act as a "challenge" to trigger a secondary immune response.
Many vaccines have multiple doses. DTaP for example is 5 shots and Polio is 4. They are also normally spread out much farther than the 3 or 4 weeks the COVID vaccines are separated. Other vaccines are more like 6 months to years apart.
For the same reason most vaccines require two doses. And for the same reason some countries are planning or doing booster shots.
Antibody levels drop rapidly after an infection, if they persist at all.
Getting a vaccination after infection re-triggers the immune system and makes antibodies more likely to persist for longer.
Reading up on this many months ago it seemed likely that natural infection plus a single vaccination would be equivalent to two vaccine shots.
There was research about only needing to give one shot of vaccines like AstraZeneca to people with previous infection. It was considered too complex to manage, and the research as to efficacy wasn’t finalised, so they stuck with two.
Having had Covid, plus two shots of something like AstraZeneca is presumably somewhere in the region of a standard two-shot-plus-booster campaign.
I don’t really understand much of this paper, but given other comments it seems to be a reasonable idea.
Why would the antibodies be more effective after 3 shots than 2? Shouldn't they be the same/similar antibodies?
Is it more a case of the 3rd dose being more recent than the 2nd dose was for participants so there are more present? If so, why are we talking about number of vaccines instead of recency of vaccination?
We also don't know the differences in immunity conferred between multiple vaccine doses and having it. We've seen cases of repeat positives spaced out over more than a month. (I work on COVID-19 testing.)
"It found that, after the second vaccine dose, neutralising antibody concentrations were higher after an interval of 6-14 weeks than after the 3-4 week regimen that was initially recommended.
When looking at the delta variant, researchers also noted that, though there were good levels of antibodies after the shorter dosing interval, levels were 2.3-fold higher with the longer dosing interval."
This isn't really "new" knowledge, double vaccine shots for other illnesses are usually spaced months apart because it usually boosts immune response and vaccine longevity. I feel quite fortunate that I got Moderna, spaced 7 weeks apart, here in Norway.
This will happen under any dosing schedule, because we already know the vaccine doesn't become effective until some time after the first dose. (Which is also one of the reasons it's hard to tell exactly how much benefit the second dose gives.)
To the best of my knowledge the first COVID vaccine dose immune response is not short-term, except in the sense that it is weaker and therefore will fade below an effective level in a smaller amount of time. But it fades at the same rate as the second dose. The second dose just "raises" the response level higher than the first dose got it.
"Some vaccines require two doses because the immune response to the first dose is rather weak. The second dose helps to better reinforce this immune response." - I would have to think over time that could be optimized somehow to just require one w/ ML and test results, etc.
It's typically because of the adjuvants added to vaccines, and some other mutations done for stability.
The major covid vaccines have fewer adjuvants (to allow for boosters) and 2 shots because that's just how the trial was run, and it turned out to work, but later testing shows they're pretty effective just with one and some countries have been delaying the second one until everyone gets their first.
Disappointing that nobody can provide a real answer. A third shot 6-8 months later seems to provide robust immunity. Same with measles or any other shot regime, which is administered over a course of several months, but not continuously and forever.
If you keep a tab on the news you might have seen antibody level from covid vaccines drops significantly over time. Actually same is true for people already have covid; natural protection wanes off within few months.
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