Too early to jump for joy over COVID-19 vaccine; here's why

Pharma giants Moderna and Pfizer recently claimed their coronavirus vaccine candidates have shown 90 per cent efficacy. This has boosted hopes of an effective jab that will work against COVID-19 earlier than expected, but what does the coronavirus vaccine efficacy mean?

It refers to the possibility that a COVID-19 shot will work on the virus patients. Drugmakers Moderna and Pfizer have said the interim results from advanced-stage studies suggest their vaccine candidates are strongly protective.

Also Read: Moderna COVID-19 vaccine 94.5% effective; can be stored in homes, clinics for 30 days

What does efficacy mean?

Moderna claimed that its experimental vaccine against COVID-19 was almost 95 per cent effective, following Pfizer's announcement that its inoculation appeared to have shown around 90 per cent efficacy. Those numbers raised hopes around the world that vaccines could help put an end to the pandemic sometime next year if they continue to show that they prevent disease and are safe.

The efficacy numbers will, however, change as the vaccine trials advance. The efficacy numbers claimed by these companies are based on fewer than 100 COVID-19 cases in each study.The early results provide strong signals that the vaccine could prevent a majority of disease when large groups of people are vaccinated. However, the actual efficacy could be known only after the final results are out once the stage 3 trials end.

Also Read: '90-95% effective': Top US health expert vouches for Pfizer coronavirus vaccine's efficacy

Minimum required efficacy

US health officials said a coronavirus vaccine would need to be at least 50 per cent effective before they would consider approving it for use. There was a concern that coronavirus vaccines might be only as effective as flu vaccines, which have ranged from 20 per cent to 60 per cent effective in recent years.

The broad, early effectiveness figures don't tell the whole story. Scientists also need to understand how well the vaccine protects people in different age groups and demographic categories. For both vaccines, the interim results were based on people who had COVID-19 symptoms that prompted a virus test. That means we don't know yet whether someone who's vaccinated might still get infected -- even if they show no symptoms -- and spread the virus.

Notably, the efficacy claims by both Pfizer and Moderna were based on the analysis of 94 patients who received the respective doses of their vaccines. Overall, Pfizer and BioNTech are conducting its stage 3 trials involving 43,358 participants.The clarity on the full-scale efficacy of the vaccine could only be known after the complete results of the phase 3 clinical trials will be out. Moderna also enrolled 30,000 participants for its late-stage trial.

Also Read: Pfizer coronavirus vaccine distribution difficult and expensive, says AIIMS Director