Covid-19 vaccine: What makes it '90 percent effective'?

The blockbuster Covid-19 vaccine announced by US pharma giant Pfizer and Germany's BioNTech SE, had a positive impact on the markets, giving a much-needed push to the global economy. 

The pharma firms revealed that the vaccine exceeded their expectations, showing it prevented 90 percent of viral infections during their third and final phase of the vaccine trial. 

Pfizer & BioNTech said they had found no serious safety concerns yet and expected an emergency authorisation from the US this month, raising the chance of a regulatory decision as soon as December.

“Today is a great day for science and humanity,” said Pfizer Chief Executive, Albert Bourla, noting the data milestone comes with “infection rates setting new records, hospitals nearing over-capacity and economies struggling to reopen.”

With the vaccine breakthrough spurring hopes worldwide, here's a closer look into its central claim--that the vaccine is 90 percent effective.  

The effectiveness percentage represents how many people out of 100 did not go on to catch the flu while being exposed to the virus. Every nine out of ten people who received the Covid-19 vaccine from Pfizer & BioNTech developed protective antibodies within 28 days after the initiation of the vaccination, which consists of a two-dose schedule.

There are still many questions, such as how effective the vaccine is by ethnicity or age, and how long immunity lasts. Also, the two pharma firms are yet to conclude whether their two-dose vaccine prevents the kind of severe cases that land Covid-19 patients in hospital. They also don't know if it stops people from carrying the virus asymptomatically.

“But the bottom line is, as a vaccine it’s more than 90 percent effective, which is extraordinary,” top US infectious diseases expert Dr. Anthony Fauci told CNN.

According to the data of US Centers for Disease Control and Prevention(CDC), the effectiveness of seasonal flu vaccines used in the last decade has varied between 19 percent and 60 percent. 

In the last five years, the flu vaccine potency rate has shown a decline. It was 48 percent in the 2015-2016 season.

In the 2018-2019 influenza season, the flu shot was 29 percent effective, far below today’s Covid-19 vaccine developed by Pfizer & BioNTech.

A recent study revealed that people who recovered from the coronavirus could have stronger and faster immune response against Covid-19 if they were exposed to it the second time.

Also, the SARS-CoV-2 antibodies could last for more than six months, which gives hope to scientists that the Covid-19 vaccine may give similar results. 

Production and distribution capacities

If granted, the companies estimate they can roll out up to 50 million doses this year, enough to protect 25 million people, and then produce up to 1.3 billion doses in 2021.

The companies have a $1.95 billion contract with the US government to deliver 100 million vaccine doses beginning this year. 

The drugmakers have also reached supply agreements with the United Kingdom, Canada and Japan.

The European Union will buy up to 300 million doses of the Covid-19 vaccine being developed by Pfizer and BioNTech, the head of the European Commission said Monday.

The vaccine must be shipped and stored at an extremely cold temperature, which requires necessary infrastructure. 

It is the case that even some US hospitals lack these sorts of storage units, which may impact when and where the vaccine becomes available in many American rural areas.