It’s Actually Encouraging That 5,800 Vaccinated People Have Contracted COVID
The CDC has released some information on breakthrough COVID-19 infections in people who have been fully vaccinated. Bad news: 5,800 people have contracted the coronavirus despite the vaccine. Good news: this is from over 66 million people, which is 0.008%.
What do we know about these breakthrough infections?
The information we currently have is from a Wall Street Journal article . The CDC has hinted that they will release additional information next week.
29% of breakthrough infections were asymptomatic. Only 7% ended up in hospitalization, and only 74 people (1.2% of breakthrough infections or 0.0001% of people who were fully vaccinated) died from COVID.
These are great numbers. They show that the vaccine is very effective and may support the idea that even if you contract COVID after being vaccinated, you are likely to get a milder illness than if you were not vaccinated. (This also applies to the flu shot.)
How does this compare to efficacy rates (eg 95% for Pfizer) from clinical trials?
This is a different calculation, so numbers cannot be compared directly. But they are compatible.
In clinical trials, one group of people gets the real vaccine and another group gets a placebo shot that does not contain the vaccine. Over time, as people live their lives, some of them will develop COVID. Researchers are comparing the risk of contracting COVID in the vaccine group versus the placebo group . This is your trial performance metric.
This differs from actual efficiency for several reasons. First, the group of subjects may be different from the people receiving the vaccine in the real world: different age groups, medical histories, etc.
Another is that over time, the virus may become more or less widespread in the world. If the total number of cases decreases, we will see fewer new infections just because there are fewer viruses.
In the end, both the effectiveness of the trials and the new data on breakthrough infections tell us that the vaccine is working really well.
How can you get infected if you are vaccinated?
When we talk about millions of people, there will always be a few cases that don’t go as we expect. Each vaccine has an effectiveness that you can test. For example, the measles vaccine is 97% effective and the mumps vaccine is about 88% effective . The effectiveness of a flu shot varies from year to year and is usually between 40% and 60% .
Why not 100%? Well, something can happen. First, not everyone’s immune system responds properly to the vaccine. People whose immune systems are initially weak may also not respond; This is why high dose flu vaccination is recommended for people over 65 .
Another possibility is that a vaccinated person can sometimes get sick when they are exposed to a virus that suppresses their immune system. This could be due to a high infectious dose (for example, someone highly contagious coughing in your face all day) and possibly other health conditions that weaken your immune system .
Finally, another possibility is that the virus may have found a way to evade a well-prepared immune system. If one of the new variants of the coronavirus has a spike protein that is quite different from the one encoded by the vaccine , your immune system may not recognize the new invader. This is why options are so troubling and why many public health experts advise us to keep wearing masks in public even when we are vaccinated.
The CDC collects information on breakthrough infections to try to determine what they have in common: are some people more susceptible to these infections than others? Are breakthrough infections associated with a specific strain or variant of coronavirus? We don’t know the answers yet, but we may soon find out.