This post was created in collaboration with Dr. Elisabeth Marnik

This new preprint, while small in numbers, does a fantastic job of outlining the immune response that occurs in breakthrough infections.

A cluster of over 1000+ infections with Covid-19 delta variant were identified in a mostly fully vaccinated population in Provincetown, Massachusetts in July 2021.

A total of 35 vaccinated individuals from this outbreak were enrolled into this study:

– 14 who tested positive for Covid-19

– 21 who tested negative for Covid-19

All those who tested positive reported symptoms of COVID-19 infection. The most common symptoms were: respiratory symptoms, fever, and loss of smell or taste. All had mild disease and none required hospitalization.

What they found:

1. Rapid increase in binding and neutralizing antibodies in vaccinated infected individuals vs vaccinated uninfected.

2. Rapid increase in binding and neutralizing antibodies in vaccinated infected individuals vs vaccinated uninfected.

3. Mucosal nasal IgA also increased quickly in vaccinated infected individuals vs vaccinated uninfected.

Importantly, these were low or below the limit of detection by the time those who were vaccinated but uninfected were tested.

However, the vaccinated infected group was younger compared to the vaccinated uninfected group. While age did not appear to correlate with the magnitude of antibody response, we do need additional data, specifically in older populations to see if this response is generalizable to more people.

Participants were vaccinated a median of 5-6 months prior.

When analyzed, responses in breakthrough infections were similar regardless of the length of time from primary vaccination. This suggests the possibility that protection against severe disease last for a long period even after antibody titers decline. This is supported by real world data showing continued protection against severe disease.

This robust immune responses following breakthrough Covid-19 infections in vaccinated individuals is very reassuring!

Why this matters?

We have a lot of data showing robust immune response in those infected and then vaccinated (called hybrid immunity).

This is the first paper that has looked at those vaccinated and then infected.

It supports the fact than infection may boost and strengthen the immune response in those who do have a breakthrough infection.

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