Corona Daily 316: Numbers 53, 106, 151

Vaccine trials can determine only the starting date, never the end date. Because the end date is contingent on events beyond anybody’s control.

Trump is pushing for a pre-election deadline. It is like asking an obstetrician to successfully deliver a four-month pregnant woman’s baby. Feeling threatened, two companies, Moderna and Pfizer, decided to be excessively transparent with the public. Moderna’s 135 page confidential protocol is now displayed on its website. In it, Moderna gives its pre-programmed milestones – 53, 106, 151. What do these numbers mean?

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Moderna planned two shots each to 30,000 participants, four weeks apart. Participants are monitored to see if they develop symptoms of covid-19 and test positive. To determine the vaccine’s efficacy, Moderna counts cases two weeks after the second shot.

Moderna’s first milestone is 53 Covid cases - fifty-three in total, irrespective of whether the case was a vaccine or a placebo recipient.

Let us imagine an extreme case, where all 53 covid cases are placebo receivers but not a single vaccine recipient has contracted the virus. This is delightful news - the vaccine is effective, the trial can end and an approval be sought.

However, dreams are perfect and life is not.

At the other extreme is a possibility of all 53 cases occurring solely among the vaccinated group, and none among the placebo-takers. If this bizarre scenario were to happen, the trial will be abandoned, the developers sacked, and the company sued.

As is usually the case, the reality will lie somewhere between these two extremes, with positive cases emerging from both groups.

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How can a vaccinated person contract covid-19, you may ask. Well, vaccines - like humans - are imperfect. The most successful vaccine – the Measles vaccine - is 97% effective. But flu vaccines are only 40%-60% effective.

Covid-19 vaccines are rushed, and expected to protect against a truly novel virus. The FDA is willing to approve a Covid-19 vaccine as long as it is 50% more effective than a placebo. 70% is desirable but challenging.

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If a vaccine is going to be effective only 50%-70%, why take it? If despite vaccination, a person can still catch the virus, what is the point? The point is this: the target of the Covid-19 vaccination programme is to achieve herd immunity, more than protecting each individual. (Sorry for the disappointing news). A 70% effective vaccine will reduce transmissibility, allow people to move around freely, and bring us back to a life more or less normal. The case numbers will be small and declining. There will still be Covid-19 cases and deaths, but not outbreaks.

That is why it is essential as many people as possible get vaccinated to get to the 70% magic herd immunity number. And people will agree to the shot in the arm, only if they have confidence in the vaccine. And they will have confidence only if there is complete transparency, and the job is not rushed.

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When Moderna reaches the first 53 cases, and if the difference between vaccinated and placebo-ed is not significant, it will wait till 106 cases, the next milestone. The placebo cases should be at least double those of the vaccine cases. If this doesn’t happen at 106, the next number is 151 (0.5% of the trial participants). Moderna will not consider asymptomatic, mild cases. So how long it – and we - will have to wait is unknown.

Ravi