As COVID-19 vaccines reach more people, some are wondering if we could delay the second dose of the Pfizer and Moderna vaccines to allow more people to get vaccinated more quickly. And, therefore, what security would the first give us.
As an immunologist, I hear this question frequently. The answer is that a single dose is very effective, but I would add that you still have to use both. However, the issue is important, not only for your personal health, but also for the health of each country.
Good news from abroad
A recent study conducted in Israel showed that a single dose of Pfizer’s COVID-19 vaccine is highly effective, up to 85%.
Sheba Medical Center reported on its experience vaccinating its nearly 10,000 employees with Pfizer’s covid-19 vaccine.
Vaccination there began on December 19, 2020, which coincided with the third wave in Israel. The researchers looked at the rate of reduction in SARS-CoV-2 and Covid-19 infection after vaccination. As of January 24, 2021, 7,214 health workers in that country had received a first dose and 6,037 had received the second.
In total there were 170 cases of infection between December 19, 2020 and January 24, 2021. Of these, 89 people, or 52%, were not vaccinated. 78 people, or 46%, tested positive after the first dose. Three, or 2%, tested positive after the second dose.
This is consistent with a new analysis of data from the phase 3 clinical trial published in 2020 in the New England Journal of Medicine. In that study, 52% protection from the first dose included infections that occurred in the first 10 days after vaccination , when the vaccine would not have been expected to have had time to generate protective antibodies against the coronavirus spike.
Using data from the published Pfizer vaccine study, Public Health England determined that the efficacy of the vaccine was 89% during the 15-21 days after the first dose and before the second dose on day 21. The range efficiency ranged from 52% to 97%.
For days 15-28, or up to the first week after the second dose, the protection from the first dose was estimated to be 91%. The range for this was between 74% and 97%. A second dose is not expected to confer immunity at that time.
Conclution
What do we know then? The Centers for Disease Control and Prevention urges people to get both doses of the Pfizer and Moderna vaccines. You should be reassured that even after just one dose of either vaccine, you have very high levels of protection since your body has time to build immunity, about a week.
The second scheduled dose of these vaccines makes them even more effective, but in an age when vaccine supplies are limited, there is much to be said about prioritizing the first dose for the greatest number of people.
William Petri, Professor of Medicine, University of Virginia
This article was originally published on The Conversation. Read the original.
