Does Vaccine Efficacy Really Matter?

22 May 2021

Discussion about Covid-19 vaccine is super hot nowadays. There is a vaccine shortage at present. Many countries are chasing after available vaccines. Even many of those not yet approved by World Health Organization (WHO) are snapped up. Why it is so?

To convince their people to take vaccine, some countries claimed the vaccines are safe & effective. Some even provide incentives to promote vaccination. This is despite there is still no approval from WHO. They are creating free publicity for the vaccine manufacturers. Why it is so?

Why?

To understand better, we'll do some simple maths. We will compare the cost of vaccines vs traditional measures to control the virus spread.

There was an outbreak recently in Singapore. A new variant called B1.167 created havoc. It infected about 400 people within a short span of a month. To control the spread, Singapore Government tested about 400,000 people. They were suspected to have close contact with the infected person. This 400,000 works out to roughly 1,000 tests per infected person.

The following table will show that it will be more cost effective for the Government to opt for vaccine. Besides being less disruptive, the effect of vaccine will last much longer.  Note that the cost excluded  treatment and all other cost which could be quite substantial as well for the traditional control method.

What Does Vaccine Efficacy Means?

Vaccine effectiveness is often measured by the term called vaccine efficacy.  It is worked out by using this standard formula.

Vaccine manufacturers are required to carry out their trials in 3 phases. Phase 1 & 2 are for testing out the safety whereas Phase 3 trial requires  30,000 people or volunteers. These people are divided into 2 groups, one fully vaccinated and the other without. These people shall live in a controlled community. They are required to live and work in virus infected environment. Their conditions are monitored in regular intervals. At the end of Phase 3 trial, their virus attack rates are used to work out the efficacy using the standard formula.

Does Vaccine Efficacy Really Matters?

There is no medicinal cure for any type of viruses found today. Viruses are known to mutate & survive in new & tougher environment.  The new variants are also known to be more infectious. One can imagine what it would be like when a vaccine  cannot "kill” and wipe out the entire virus colony.

How Vaccine Efficacy Matters?

Take the case in Singapore again. The present outbreak had 78 infected among the 400 people.  These 78 people  had full dose of vaccine. This translated to a total testing cost of about SGD$72 millions as shown earlier.   This was because the vaccines used in Singapore has a vaccine efficacy of 95% . What would this testing cost if the efficacy was 60%?

To work out this number, we can use the efficacy calculation template as shown in this webpage. We can change the number in row 10 or the "number of fulldose infected". Now,  if we change this row 10 number to 320 instead of 78, we should get the vaccine efficacy number to be roughly 60%. 

    In other words, if Singapore's vaccine were 60% and not 95%,   Singapore Government would have to spend another $57 millions on testing cost. The total testing cost would then be $129 millions and not $72 millions. 

     Using the same method by changing the numbers in row 10,  we can plot this following chart that will show the vaccine efficacy vs % vaccinated people infected.  

In conclusion,  Vaccine efficacy really matters.  To control the spread of Covid-19 using vaccine of lower efficacy will jack the testing cost by inversely proportional amount. 

 

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