The vaccines currently available in the US to prevent COVID-19 have proven remarkably safe and highly effective thus far. But, since no vaccine is perfect, we expect to see occasional infections even after full vaccination.
And we have. More than 10,000 of these so-called breakthrough cases of COVID-19 have been reported in the US. Seems like a large number, right? But keep in mind that nearly 133 million people have been vaccinated, so these breakthrough cases represent less than one in 10,000. It’s safe to assume that not all breakthrough cases are being reported, of course, but so far that’s a remarkably low failure rate!
Because the vaccines help prevent severe infections, most breakthrough cases are mild or moderate. Should we keep tracking those, or should we focus only on severe cases — those that lead to hospitalizations, ICU stays, and, more rarely, deaths? That’s the question the CDC recently answered by deciding to focus only on cases that require hospitalization.
What can all breakthrough cases tell us?
While that approach may not seem unreasonable, it certainly has disadvantages. Because COVID-19 is a new disease caused by a novel virus and the vaccines were only recently developed, studying breakthrough cases could tell us a lot. For example:
- Are factors related to the different vaccines responsible?
- One type of vaccine might be less effective than another.
- Manufacturing problems might make certain lots of a vaccine less effective.
- Problems with storage or thawing, or errors in vaccine dosing, might lead to vaccine failure.
- The timing of the second vaccine might play a role, whether given earlier or later than recommended.
- Are factors related to people who get vaccinated important?
- Differences in failure rates might be based on age, gender, ethnicity, medication use, or immune function.
- Apparent vaccine failure might occur due to a lack of mask-wearing, physical distancing, and/or exposure to an infected person just prior to full vaccination.
- What about factors related to the virus?
- Certain mutated versions of SARs-CoV-2 — the viral variants of concern — may be over-represented among breakthrough cases. We don’t know yet, because a genetic analysis has been done in relatively few of these cases. If correct, it would suggest that available vaccines are less effective against certain variants, a discovery that could lead vaccine makers to modify them.
Besides getting a better understanding about why breakthrough cases occur, it would be helpful to figure out why some breakthrough cases are mild while others are severe. And we need to learn whether people who develop a breakthrough infection should receive a booster shot of vaccine after they recover.
Oregonstate News Blog 