What’s the Best Covid Vaccine? Why It’s Not So Simple


As scientists raced to develop Covid-19 vaccines, public health specialists were hoping that more than one group would succeed. Having multiple companies producing vaccines would make it easier to inoculate a lot of people fast. Be careful what you wish for. A range of vaccines with different efficacy results now has given rise to worries that some people may refuse the shot on offer in hopes of getting a “better” one later. In reality, comparing efficacy numbers isn’t necessarily the best way to measure a vaccine’s value. And as suppliers struggle to meet global demand, experts say the best vaccine for you is probably whichever one you can get now.

1. What does efficacy mean?

On a basic level, vaccine efficacy of 50%, for example, roughly means that an immunized person has a 50% reduced risk of becoming ill compared with an otherwise similar non-immunized person. However, the measurement can be applied to different questions about a vaccine’s effect. For example, several Covid-19 vaccines appear to successfully — 100% — avert hospitalization and death. But since relatively few people infected with SARS-CoV-2 become critically ill, it’s hard to measure such a rare outcome reliably in clinical trials involving only tens of thousands of participants — a relatively small pool. Instead, the primary aim of most late-stage trials has been to measure broader efficacy against lab-confirmed Covid cases with any symptoms, including mild ones.

2. What efficacies are being reported?

The first two Western vaccines to prove effective — one from Pfizer Inc. and BioNTech SE, and another from Moderna Inc. — set a high bar, with efficacy estimated at 95% and 94%, respectively. That means that Covid cases among trial participants who received the vaccine were reduced by that much compared with those who got a placebo. Efficacy was estimated at 66.7% for AstraZeneca Plc’s and 89.3% for Novavax Inc.’s two-shot regimens; and 66.9% for Johnson & Johnson’s single-shot vaccine. Four vaccines from China and one each from India and Russia are reported to have efficacies ranging from 50% to 91%, summarized below.

Source: https://www.bloomberg.com/news/articles/2021-03-10/what-s-the-best-covid-vaccine-why-it-s-not-so-simple-quicktake