What to think about vaccines today, including why vaccines protect you against blood clots

Georgette's comment to my other post prompted me to write a new post on current Covid-19 topics.

Vaccines protect you against blood clots

They didn't say it out loud but they imply it. Keep reading...

The FDA's pause on the Johnson & Johnson vaccine is a significant event. The situation parallels the controversy over many European countries halting the distribution of the Astrazeneca vaccine. My take is the same as before. The only unknown is whether the FDA will issue an additional warning about rare blood clots that affect certain subgroups of people. They are likely to keep recommending the vaccine to most of us.

The circumstantial evidence related to blood clots is accumulating. Both J&J and Astrazeneca vaccines use the adenovirus technology. These blood clots are happening mostly to young women, and are paired with other conditions (low platelets), which makes natural cause being rather unlikely. The diagnoses and demographics of the affected people are similar across both vaccines, and, though rare, the same condition has popped up in numerous countries.

The cost-benefit analysis for the young female demographic is completely different from the average person. The benefit of the vaccine is much lower, given the tiny mortality rate from Covid-19 (not counting the benefit accrued to others). Meanwhile, the cost of serious illness and death from rare blood clots is relatively higher because the baseline risk of this condition is minuscule for that age group. A preliminary estimate by the European Medicines Agency (EMA) found that for the younger population, the reported cases of those rare conditions were 5 - 12 times higher than expected.

Doctors are justifiably alarmed, given the "do no harm" principle. Side effects have always been the challenge of developing vaccines. Injecting otherwise healthy people with a substance and causing harm is not accepted, except in a pandemic. The risk to most people is still low but it doesn't then follow that the risk is low to all.

The statistic of the moment says the overall incidence of blood clots is far, far lower than expected among those who were vaccinated. Therefore, they say, the vaccine does not cause blood clots. The gaping hole in this argument is that the data present strong evidence that these vaccines protect people against blood clots! If the vaccines have nothing to do with blood clots, then we expect similar incidence among the vaccinated as among the unvaccinated, and both rates being similar to the expected value. Instead, they tell us blood clots are far less common than expected among those who got the Astrazeneca shots.

I support the FDA's pause decision. It builds confidence that the agency is keeping an eye on safety as there are plenty of examples of medicines that have side effects that are not found during a clinical trial. I hope they look beyond case counts, and review other information as well. Recall my post on the law of small numbers.

Fully vaccinated people does not have a 5% chance of catching Covid19

Your chance of catching Covid-19 after getting fully vaccinated is not 5%. It cannot be that high. If you review the data from all the vaccine trials, the typical case rate on the placebo arms is 2-3 percent. That means, of those participants who were given placebo shots during the trials, 97-98 out of 100 did not get symptomatic, confirmed Covid-19. If the chance of getting infected after 2 vaccine shots was 5%, then the vaccine would have negative efficacy (worse than placebo)!

The source of this confusion reflects a misunderstanding of a vaccine trial. Vaccine trials are different from the usual clinical trials of drug treatments. In a cancer drug trial, every participant has cancer. In a vaccine trial, we don't know who has been exposed to the coronavirus. In a short trial, with only half the participants reaching 8 weeks of observation, most of the uninfected probably have not been exposed yet.

Giving a probability of getting infected without stating a time window is also useless. If the 5% number came from the trial results, then the right way to describe it is 5% within two months (which, if you think about it, is disturbingly high).

Vaccines and the cargo cult

There is a cargo cult developing around vaccine science. Vaccines have become the single and only explanation for positive trends while not enough vaccines is the single and only explanation for negative trends.

For example, the U.K. and Israeli governments credit their fast vaccine rollouts as the reason for plunging cases. To do proper science, we must take into account all other factors, and in particular, the impact of national lockdowns - which coincided with the vaccination campaign - and the reversal of the holiday spike.

The vaccines-only narrative lends support to lockdown skepticism, mask skepticism, and social-distancing skepticism. Those brands of skepticism also weaken our national fight against the coronavirus.

All vaccines are the same

Vaccines are not all the same. To believe that a VE 60% vaccine is the same as a VE 90% vaccine is to believe that the scale for measuring VE is severely flawed. To believe that vaccines using different technologies and formulations are all the same is to believe that formulations and technologies are window-dressing. Even if all vaccines were identical, people still have preferences: some go for a black car, others a red car - even when it's the same car.