Vaccines and Probabilities

April 9 2021

Many years ago as I tried to tell sceptical people that smoking killed people, the research was all about the probability of smokers getting diseases more often than non-smokers.  People would often reply, ‘Lies, damn lies and statistics’ as if this was some sort of frightfully clever response that neutralised any sensible discussion.

Statistics have been used by researchers for years and are the basis of the experimental method to get towards scientific truth.  Things are rarely ‘proved’ in science, they are just rendered more and more likely, so that the probability of their not being true becomes infinitesimally small. 

Where there are number of variables the statistics become ever more complicated and the proofs more arguable.  Some of us get a bit lost as the complexity rises, and try to retreat to ‘common sense’, with is another way of saying what is most probable based on facts we are already sure of. 

The Astra-Zeneca vaccine has been pushed in Australia, and there is a world shortage of vaccines, despite Prime Minister Morrison running around with an open chequebook for a long time and boasting that we were at the front of the queue for was it 4 different ones ‘in development’?

The loss of the Uni of Qld. vaccine because it gave a false positive in the HIV/Aids test was a bad blow, given that it was ‘ours’ and the vaccine against cervical cancer had been so successful. 

As more and more countries expressed reservations about the A-Z vaccine, it was becoming harder and harder to stick to the line that they were panicking and there was nothing in the stories about blood clotting in dangerous body locations. 

Now A-Z  is not recommended for the under 50 age group, which is most of the country.  Presumably this means that because under-50s are less likely to die of COVID19 even if they get it, the risk of dying from a clot becomes more significant.  Obviously in Australia, if we can keep COVID isolated forever, we will not need a vaccine at all unless we want to venture overseas.  So we are looking at the probability of the virus escaping, and the probability of other vaccines being available as well as the chance of dying at whatever age we are with whatever existing medical problems we may have, versus the chance of having a bad reaction to the vaccine. 

I want to get vaccinated so I can go on an overseas holiday at last, but the A-Z vaccine may be less effective against new and dastardly strains, and if I take that risk will I be stuck in a hotel in Mongolia unable to fly home because the government has changed its policy on my vaccination status or the absolute numbers who can be quarantined?

It is very hard to answer all these questions for anyone, and when older patients who have clotting problems ask for advice, it is very hard to give them an answer.  Doctors will have to spend a lot of time on this.   Our practice is not vaccinating at all, the red tape scared us off, despite the fact that we had bought a new vaccine frig and have been vaccinating people for 40 years.  Call me a coward if you will.  But for myself, I do have an appointment to have the A-Z vaccine next week.

Here is the SMH article:

AstraZeneca blood clot cases force major vaccine shake-up; Pfizer now preferred for under-50s

By Rachel Clun

April 9, 2021

Pfizer is now the preferred vaccine for people aged under 50 and the timing of Australia’s rollout is in doubt after medical experts expressed concerns about rare blood clots potentially linked to the AstraZeneca vaccine – the mainstay of the country’s existing COVID-19 strategy.

Prime Minister Scott Morrison said on Thursday night the government will review Australia’s vaccine portfolio and accept medical advice that will preference the Pfizer vaccine over AstraZeneca’s in adults aged less than 50 years old who have not already received a first dose of AstraZeneca, putting plans to vaccinate the entire population by October in doubt.

Australia’s decision follows changes by European medical regulators after a review of data confirmed a rare blood clotting condition seen in a small number of patients was linked to the AstraZeneca vaccine.

Mr Morrison said the new advice from the Australian Technical Advisory Group on Immunisation was not a prohibition on the use of the AstraZeneca vaccine in people aged under 50.

“This is not a directive. This is not an instruction,” he said, noting they were taking “an abundance of caution” with the new advice. He said the impact of this decision on the timeline of the rollout was uncertain.

“Tomorrow, and over the weekend, there will be a recalibration of how the program will need to be adjusted to take into account decisions the government’s taken tonight to accept those recommendations from ATAGI,” he said on Thursday evening.

Chief Medical Officer Professor Paul Kelly said the rare but serious blood clot disorder was discussed in the meeting, taking into account what was decided overseas and looking at what that would look like in Australia.

“This is a rare event,” he said. “But it is serious and can cause an up to 25 per cent death rate when it occurs.”

For those over 50, Health Department secretary Professor Brendan Murphy said AstraZeneca was strongly recommended.

“It is a vaccine that is very, very effective,” he said.

ATAGI spent hours on Thursday considering the medical evidence. It then issued new advice on the AstraZeneca vaccine, which it provided to the government just after 7pm.

The medical experts made three recommendations, including that AstraZeneca was preferred in adults over 50, after a lengthy meeting. They also recommended adults under the age of 50 should only be given AstraZeneca where the benefits clearly outweighed the risks. Third, it recommended that adults under 50 who had already received their first doses without experiencing serious side effects could safely be given their second dose.

Professor Kelly stressed the data on the rare clotting side effect, venous thromboembolism, was still only preliminary.

Britain’s vaccine advisory committee says adults under 30 should be offered an alternative to AstraZeneca’s COVID-19 vaccine when possible, due to a very rare side effect of blood clots in the brain.

“There are very few cases of this extremely rare event that have happened anywhere in the world, but the ones we’ve seen, there’s definitely a tendency for the younger people [to develop it],” he said.

The UK regulator has decided to offer an alternative vaccine for those aged under 30.

Australia has purchased 20 million doses of the Pfizer vaccine and has been relying on the AstraZeneca vaccine as the workhorse of the rollout. The country is expecting its first deliveries of the Novavax vaccine, pending regulatory approval, some time in the fourth quarter of the year.

Late on Thursday, Australian pharma giant CSL said “it remains committed to meeting its contracted arrangements with the Australian government and AstraZeneca for locally produced AstraZeneca COVID-19 vaccines.”

AstraZeneca Australia added that it respected the decision outlined by the government.

“Regulatory agencies have reaffirmed the vaccine offers a high-level of protection against all severities of COVID-19 and that these benefits continue to far outweigh the risks.” a spokeswoman for the company said.

Earlier, the Prime Minister said the risk of severe side effects with the AstraZeneca vaccine is much lower than with common drugs including paracetamol and the oral contraceptive pill.

Mr Morrison said it was important to know the risk of developing venous thromboembolism was much lower following the AstraZeneca vaccine than the risk of death from COVID-19.

“Let’s note that in the UK, the advice is that some 6000 people’s lives have already been saved by this very vaccine. So we need to consider the positive benefits,” he said.

From UK data, the risk of venous thromboembolism following the vaccine was about one to five per million people.

“To put that in some sort of perspective, the combined oral contraceptive pill, that can include adverse side effects of venous thromboembolism – that’s seven to 10 per 10,000,” Mr Morrison said.

The advice has been shared with the expert medical panel, the Australian Health Protection Principal Committee, which comprises all state and territory chief health officers and led by federal Chief Medical Officer Professor Paul Kelly.

The matter will also be discussed in national cabinet on Friday and in meetings with state and territory health ministers, who were due to meet on Thursday night to discuss the revised advice and its implementation.

On Wednesday 75,880 doses of the Pfizer and AstraZeneca vaccines were administered across the country, Scott Morrison said, taking the national total to 996,214 doses administered so far during the rollout.

The states and territories have administered 509,802 doses. Through the federal government, 486,343 doses have been administered, including more than 125,260 through aged care.