What should I do about the large discrepancies in vaccine efficacy against the Delta variant being reported across studies?

COVID Variants Vaccines

A: Delta variant, waning immunity, imperfect measurement, or something else? There are a number of reasons why COVID-19 vaccine efficacy may differ across studies.

These new reports are measuring the effectiveness of the vaccines in real world settings instead of in a clinical trial. Isolating individual variables in a real-world setting can be difficult. Instead, scientists rely on a collection of studies versus a single study to make decisions. Here is what we know (and don’t know) thus far.

Vaccine effectiveness is less than 100% and more than 0% for nearly everyone who received a COVID-19 vaccination. Unfortunately, the exact vaccine effectiveness is not clear and likely a moving target. A study from the United Kingdom published in the New England Journal of Medicine reported vaccine effectiveness of 88% against the Delta variant among people fully vaccinated with the Pfizer vaccine. In the same study, vaccine effectiveness against the Delta variant was 67% among those who received two doses of the AstraZeneca vaccine. The Israeli Ministry of Health recently reported vaccine effectiveness of 39% against the Delta variant after 2 doses of the Pfizer COVID-19 vaccine. The data from this study and methodology are not available at this time. In a third study conducted in Canada, the Pfizer COVID-19 vaccine effectiveness against the Delta variant after two doses was 87%, similar to previous variants of concerns. A pre-print of this study is available, prior to undergoing peer review.

LUCKILY, multiple studies repeatedly find that vaccinations continue to provide strong protection against serious illness and death in the setting of the Delta variant. Expect continued research on the following topics:

1) Who is at highest risk for severe breakthrough infections following vaccination?

2) How can we successfully vaccinate more people to decrease transmission and the development of new variants?

3) How much does waning immunity influence decreased vaccine efficacy against Delta and other variants?

There are several things you can control as additional information becomes available.

Now is a good time to reconsider COVID-19 vaccination if you have not already received it. The evidence continues to show that COVID-19 vaccinations decrease the risk of contracting COVID-19 and greatly reduce the likelihood of developing severe illness and complications.

Layer on the mitigation measures. Vaccination alone is insufficient to control the pandemic at this moment. In the setting of increased virus transmission in most areas, the likelihood of encountering COVID is higher AND the Delta variant is better at moving from person-to-person, even among the vaccinated. Thing of risk mitigation measures as a dial instead of an on/off switch and dial up the mitigation measures. Avoid crowded spaces, wear masks, increase air circulation with filters indoors, move events outdoors when possible, reduce the size of networks, keep indoor outings short. Additional risk mitigation measures become key tools in the setting of high community spread of the Delta variant and potential waning of immunity over time.

Boosters are not yet widely available, but are likely in the future. It remains unclear when and for whom boosters will be recommended. Immunocompromised people and older adults may require boosters before the general public to attain and maintain protection from severe consequence of infection such as death.

Last and most importantly, we need to work together to maintain critical infrastructure and protect people without the increased protection of vaccines. Delta will challenge schooling for our children, the economy, employment, manufacturing, food supply chains…. the list goes on an on. COVID sucks. It’s virus against humans and we need to work together.

Additional Resources:

Study Published in the New England Journal of Medicine

New York Times Summary of Vaccine Efficacy Concerns

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