Breakthrough Infections: Do COVID vaccines work against Delta?

Wouldn’t it be great if we had a vaccine that was 100% effective with zero side effects? Unfortunately that is not the reality of the pandemic, or vaccines (or viruses) in general for that matter. Still, one can wish.

The recent spike of illnesses associated with the SARS-CoV-2 Delta variant has yet again called into question the efficacy of vaccination.  We are hearing of “breakthrough” infections, meaning infections in people already vaccinated against the disease. Just last week, a  smart and thoughtful friend of mine told me that he was skeptical of the vaccine for two reasons: the lack of full FDA approval and breakthrough infections. He specifically mentioned the outbreak involving several vaccinated individuals in Massachusetts. 

We will discuss FDA approval another time (spoiler alert: it’s coming soon), but I’d like to address breakthrough infections now, and we will use the Massachusetts outbreak above as a good case study. 

Before we get into the data, we need to take a step back and re-adjust our thinking about the term “effective” when it comes to vaccines. (Note: if you are anti-vaccine, this is an appropriate time for an eye roll). 

Seriously, anyone who ever thought that getting the vaccine would 100% protect you against ever getting the virus needs to stop and think about how vaccines work. It’s not as if there is a magic force-field that surrounds you and causes virus particles to bounce off of you when you take the vaccine. Instead, vaccines teach your body how to fight the virus when you do get infected. This is the way all vaccines work. Successful vaccines (like the ones we have available for COVID-19) result in a quicker, more robust immune response which leads to a shorter, often asymptomatic infection. In addition, when your immune system can fight the virus more quickly and vigorously, you should shed less virus and thus be less likely to infect other people. 

So, vaccine “effectiveness” can be measured in several ways. Ideally vaccinated people will have no illness, or a short asymptomatic infection during which they do not pass the virus on to other people. The reality is that the vaccines currently available are “only” 95% effective against the original SARS-CoV-2 virus, and probably closer to 85% effective against the Delta variant, although it is still a little too early to tell. Do you know 100 people who have been vaccinated? You probably do, and for about 15 of those, the vaccine will not be effective against Delta. That’s just statistics. 

Now let’s return to the Massachusetts outbreak. In early July of this year, multiple summer events and large outdoor gatherings were held in Provincetown. Throughout the state of Massachusetts, 69% of eligible residents are vaccinated, but we do not know the exact vaccination rate of those in attendance. It should be noted that many out of state residents were present at the event, which included “thousands of tourists.”  In the days leading up to the event, Barnstable county had zero cases of COVID reported (14 day moving average).  Beginning on July 10, an outbreak of COVID resulted in which 469 cases of COVID were reported. Of these, 346 (74%) cases were among fully vaccinated individuals (two doses of Pfizer or Moderna, or one dose of Johnson and Johnson). Five individuals were hospitalized, including 4 individuals who were fully vaccinated. Thankfully no deaths resulted from the outbreak. 

At first glance, this incident gives credence to the idea that vaccines do not work against the Delta variant, but let’s look at the numbers a little more closely. Nationwide and in Massachusetts, the hospitalization rate for COVID-19 infections has been pretty steady throughout the pandemic at 9%-10%. That means that 9-10% of people diagnosed with covid, regardless of vaccine status, age, comorbidities, etc will end up in the hospital. However, only 1.15% (4 out of 346) of vaccinated individuals who acquired COVD-19 during the Massachusetts outbreak were hospitalized. That is what a successful vaccine looks like. 

This can be difficult to reconcile. On the one hand, I want to be vaccinated in order to protect myself and those around me. On the other hand, as the Barnstable county example makes clear,  I can still get COVID even if I am vaccinated. What’s worse, a new study from China seems to indicate that vaccinated people can spread the virus to those around them. This reality forces us to first remember the way vaccines work (outlined above) and second, re-examine our reasons for vaccination. At this point, the overriding reason for vaccination must be to keep Americans out of the hospital, keep Americans from dying unnecessarily, and contribute to the effort to overcome the pandemic. 

In the spring of 2020, I mistakenly believed that the virus would likely burn itself out during the summer months. In the fall of 2020, I was hesitant about the vaccine and even advised against it. (You can read about that here). Earlier this year, I hoped that the combination of vaccine immunity, infection immunity, and summer weather (I’m hard headed) would combine to overcome the pandemic. I (and many others smarter than me) are now convinced that only a robust vaccination rate leading to herd immunity will be enough to rid ourselves of the endless mask mandates, vaccine debates, and tragic illness burden we find ourselves with today. 

Again I urge you to separate science from politics, get your information from reliable sources, and speak kindly to one another about the pandemic and the vaccine. We face a common enemy. Working together we will overcome it.