What you need to know about the outbreak of the delta variant SARS-CoV-2 in Provincetown, Massachusetts

NS Development of delta variants of SARS-CoV-2 in most vaccinated populations In Provincetown, Massachusetts, it was reported by the CDC on Friday, boosted by public events and rallies.

The concern with this cluster is that the majority of the identified cases were among people vaccinated with the Pfizer-BioNTech, Moderna, or Johnson & Johnson vaccines.

The CDC report provides 469 statistics identified by July 17th. NBC Boston, The total number of cases increased to 882 cases.

There was a significant infection among fully vaccinated people

Of these 469 cases, 346 (74%) occurred in complete vaccinations. These results indicate that infection of vaccinated people can occur with sufficient regularity to cause the outbreak.

For comparison, the report states that the vaccination rate among eligible residents of Massachusetts was 69% at the time of the outbreak. It should not be concluded that this means that the vaccine was ineffective in preventing infection in this population. To estimate efficacy, it is necessary to know the proportion of the actually exposed population that has been vaccinated. There are several reasons why outbreaks in exposed populations may not meet our expectations. First, there are geographical differences in vaccination rates within the state. Second, “breakthrough” cases of infection are always present, and as the population approaches full vaccination, more and more cases occur among vaccinated people and are falsely effective. Make an impression. Third, there may be behavioral differences between vaccinated and unvaccinated people. In particular, if a vaccinated person feels safer than an unvaccinated person, he or she can reasonably expect to take more dangerous actions, such as attending a large rally.

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In particular, all genetically identified cases Delta variant.. It is currently unknown whether the genetic makeup of the delta mutant was particularly important in promoting this development.

Fully vaccinated people with symptomatic breakthrough infections can infect Delta as much as unvaccinated people

Another important finding in this study was that there was no evidence of differences in the “Ct values” of virus samples taken from vaccinated and unvaccinated individuals. “Ct” is an abbreviation for “cycle threshold” and refers to the number of chemical reactions required to amplify the genetic material of a virus so that it can be detected by the following process. Real-time reverse transcription PCR.. This is important because the Ct value usually correlates with viral load. Viral load has been found to be an important contagious factor. At face value, this suggests that if vaccinated people become infected and have symptoms, they can infect as much SARS-CoV-2 as infected and unvaccinated people. doing. Importantly, the number of asymptomatic and infected vaccinated people is unknown, so it is not possible to draw a firm conclusion about the impact of vaccination on the potential for infection.

Does this mean that the vaccine is ineffective against delta mutants?

In a nutshell — no. Vaccines are very effective in preventing death and serious illness. As of July 27, approximately 1% of provincetown cases in vaccinated people were hospitalized (only 4 out of 374). This is compared to the typical hospitalization rate of about 10%. (I calculated this by looking at the total number of hospitalizations reported by the CDC COVID-NET, Multiply by 10 to reflect the total population of the United States and divide by the current cumulative number of cases reported (a little less than 35 million). In addition, none of the 374 people have died, but the overall case fatality rate in the United States is currently around 1.7%.

Moreover, if only a small part of the population of Provincetown and Barnstable County had been vaccinated, there is no way to say how big the outbreak would have been. The outbreak of hundreds of people in counties with a population of over 200,000, especially given the social conditions of “dense indoor and outdoor events at venues such as bars, restaurants, guest houses and rental housing”. It is said that there are relatively few. NS CDC report..

Conclusion

Conclusion: There are some things we really want to know, but we can’t learn from these data.

1. What is the effect of vaccination on the potential for infection once exposed?
2. What is the impact of vaccination on the potential for infection once infected?

Nevertheless, there are some important lessons we can learn.

1. Large-scale rallies are still an important superspreader event, even among vaccinated people.
2. Individual behavior is almost certainly associated with infection risk. A crowded congregation should be avoided, even if fully vaccinated.
3. The outbreak can occur soon. On July 3, the 14-day moving average in Barnstable County was zero. By the time the incident occurred, it was too late to take action.Therefore, the CDC’s new guidance is Even vaccinated people need to wear a mask indoors Sage’s advice in many places.