UW News

April 13, 2021

Vaccines debate: ‘Escape variants’ of the coronavirus are a serious future threat

UW News

gloved hand holds vial of vaccine

Should doses of the two-shot vaccines be spread out by months instead of weeks to get more first shots in shoulders?

With COVID-19 cases on the rise again in many parts of the country — including Washington state where three counties were pushed back to Phase 2 effective Friday — there’s a growing debate between continuing to give both doses of Moderna or Pfizer-BioNTech vaccines close together, or giving them months apart in order to get first shots in more shoulders faster.

The argument for giving more people the first dose before circling back months later to give the second, which provides the strongest protection against COVID-19, centers on the numbers: It’s better, the argument goes, for more people to be partially protected in order to curb infections by the coronavirus than to have fewer people fully vaccinated. Advocates of this “dose-sparing” strategy hope partial vaccinations would not only curb infections but also save lives, since a single dose can provide significant protection against illness.

Under the current strategy, the second dose of either two-dose vaccines comes within a few weeks of the first shot. The dose-sparing strategy, considered either because a community has too few doses or climbing infections, schedules the second dose for months later.

Larry Corey

Larry Corey

However, the dose-sparing strategy could create even greater trouble than we’re currently facing, argues the University of Washington’s Dr. Larry Corey in a recent COVID-19 Vaccine Matters blog jointly produced by Johns Hopkins University and the UW.

“I say that because the viruses we’re going to encounter today and what we will encounter in the next several months are not the same viruses that we tested the vaccines on and upon which the single-dose [strategy] data are based; they are going to be more formidable adversaries,” writes Corey, a professor of medicine and virology at the UW School of Medicine.

These future versions of the viruses are “escape variants” that have evolved in the environment of weak immune responses — the body in this case has produced a strong enough immune response to tamp down the infection but not strong enough to keep mutated viruses from spreading.

“How do we overcome escape variants? We do so by using the full strength of the tools we have available to us. We provide immunity that is capable of eliminating the virus quickly and we don’t expose the virus to lots of people with low levels of immunity,” Corey writes.

Corey adds that the coronavirus variants currently spreading require a stronger immune response to beat, and current versions of the two-dose vaccines were designed to battle the original versions of the virus. So, using one dose to create partial immunity to a variant that requires a stronger immune response to beat could create an environment for new, tougher variants to evolve and spread. However, giving the second dose creates a much stronger immune response and can stop escape variants.

“While my musings are inferential, I feel we will actually do more harm than good by markedly increasing the population of people with partial protective immunity,” Corey writes.

To read this and other articles by Corey and other experts, visit the COVID-19 Vaccine Matters blog series created by Johns Hopkins and the UW as an outcome of the joint symposium — Preserving the Scientific Integrity of Getting to COVID-19 Vaccines: From Clinical Trials to Public Allocation — the two universities hosted in October.

Dr. Larry Corey is the leader of the COVID-19 Prevention Network (CoVPN ) Operations Center, which was formed by the National Institute of Allergy and Infectious Diseases at the U.S. National Institutes of Health to respond to the global pandemic and the Chair of the ACTIV COVID 19 Vaccine Clinical Trials Working Group. He is a Professor of Medicine and Virology at University of Washington and a Professor in the Vaccine and Infectious Disease Division and past President and Director of Fred Hutchinson Cancer Research Center.