There are three broad types of vaccines. All “infect” some of your cells produce part of the virus. Your body generates antibodies and T-cell responses that protect you from being infected by the virus in future.
Traditional vaccines use an “attenuated” or “killed” whole virus. There are COVID vaccines of this type developed in China and India. Other COVID vaccines use novel techniques to deliver parts of the virus’s genome as a way of “infecting” cells. Put crudely, the mRNA vaccines like Pfizer’s use a “lipid shell” (a fat layer!) to surround a the piece of genome that replicates the “spike” protein for the immune system to attack. The shell enables the mRNA to pass a cell wall to infect it so it produces these antigens (the thing the antibodies attack).
The recent vary rare cases of an unusual blood clotting problem have led to the suspension or restriction of the Janssen (J&J) and AstraZeneca vaccines. Both are the third type, adenovirus vector vaccines. Here developers take an existing virus that is harmless but infects humans. (AstraZeneca chimp flu, J&J human cold viruses) They “splice in” the relevant section of COVID-19 virus’s genome. The body produces an antibody response against the “carrier” virus and against the COVID section.
On a cell level, they are sitting happily doing their thing of absorbing enough amino acids to be able to duplicate their genes and divide. A bit like a photocopier you have to load with enough paper to copy a 1000 page document. The adenovirus hijacks the replication process. Like someone asking to copy a page and then doing 1000 copies. At some point the antigens break out to infect other cells. The immune system’s “killer” cells stop duplication by the infected cell. Antigens are busy finding the right block for the new antigens they have encountered. The memory-T and B cells are being “programmed” to produce new antibodies against a future COVID infection
All the COVID vaccines are given into the muscle mass at the top of the deltoid muscle (the chunky bit you feel when you squeeze your arm just below the shoulder.) The tight proximity of the muscle cells and general lack of larger blood vessels mean the infection and immune response will affect a limited Harea.
The extremely rare blood clotting problem is associated with low platelet count. This is why the CDC have publicised the need to be cautious about using heparin for blood clots as this lowers platelet count. This syndrome can also be a very (previously believed more) rare side-effect of female oral contraceptives.
Those of you who follow the nurse-trainer Dr John Campbell will know that he has occasionally remarked about how pictures show injections into the wrong part of the deltoid. He speculated when the clotting problem first came to light that it might have something to do with wrong technique. He strongly suggests reversion to the old aspiration protocol of giving vaccinations. This involves inserting the needle, injecting part of the dose and drawing it back up into the syringe. If it is clear, the whole injection is given. Blood in the sample means possibly injecting into a vein.
This speculation seems to be borne out by a paper he had found published early in the development of adenovirus vaccines. These were initially only used in gene theraphy, their use in vaccines is novel. Gene theraphy vaccines are designed to be given intravenously so that all the body’s cells are eventually “infected” by the corrected genes. There are known immune responses to these vaccines but the risk outweighs the life-saving benefit. The paper John found relates to experiments administering adenoviruses intravenously.to mice. The researchers found cases of low platelet-count associated blood clots. The mechanism appears to be that the adenovirus infects platelet cells which become “stickier”are then surrounded by white cells to dispose of them. This forms a “seed” for more platelets to stick to and form a blood clot.
But let John explain it better and more scientifically. Don’t worry, he uses a very outsize syringe and needle with red ink to illustrate the point.
I must admit I find John’s reasoning to include aspiration in the protocol compelling, if even out of an excess of precaution.
In all this it is important to remember how rare incidents of this sydrome are. The risk is over 1 million to one of getting a thrombosis and one in 7 affected died. Also follow the CDC and your doctor’s advice if you have symptoms after a J&J vaccination.
People should also not be concerned if they have had the first dose and the second is delayed because of supply problems The protocol in the UK is to delay the second dose to up to 12 weeks. This applies to both the Pfizer and AstraZenica vaccines. With over 61% of the adult population with one dose, the vaccines are providing protection from serious illness needing hospitalisation and death and is stopping the virus. Deaths are down to (a too many) 20 a day.
One dose breaks the link, remembering full protection builds up over several weeks. The second dose will give you better immunity from any infection and will extend the protection. Even after the wait for the second dose to take effect, you should still take appropriate masking etc precautions to limit your exposure to the virus. You can still be infected by COVID, depending on how long since vaccination and other factors like viral load, your immune system will fight it. You could eliminate it completely or you could get an asymptomatic or mild disease. Although there are indications it is unlikely, you could still pass on the virus.
As ever it’s a personal assessment of the risk. You would be relatively safe dinng with a group of friends who have all been vaccinated compared to a Florida beach at Spring Break. Older vaccinees may consider the theraputic effect of hugging their unvaccinated grandkids to outweigh the outside risk of having a mild or even moderate illness.
If you apply the same risk analysis to the Janssen vaccine: mortality from COVID is around 0.2%; mortality risk from this vaccine complication is less than 0.00002%. If there are precautionary age or sex restrictions on its administration when it its use restarts, this risk will be even lower.