What’s the Difference Between a Strain and a Variant?

Variant and strain are often used interchangeably during the pandemic, although they have different meanings.

When a virus infects a host, it needs to replicate itself to target more cells. However, these replicas might evolve and mutate in the process. When the virus has one or multiple distinct mutations that appear to be a pattern, it becomes a variant, according to Andrew Pekosz, PhD, a virologist at the Johns Hopkins Bloomberg School of Public Health.

A strain, on the other hand, “is a variant that has accumulated a lot of mutations that essentially change the way the virus behaves in a drastic way,” Pekosz said. Strains have a demonstrably different functional property or behavior from the original virus.

Alpha, Beta, Gamma, Delta, and Omicron are all variants of COVID-19. Omicron, for example, has more than 30 mutations in its spike protein, the part that allows the virus to latch onto and enter human cells.

This is where it gets tricky. For some, the changes in Omicron—or all of these variants—are significant enough to be considered strains.

“Omicron was close to being a new strain of SARS-CoV-2, but most scientists didn’t think it changed enough to move from variant to strain,” Pekosz said. “It’s a bit subjective when to use the term strain.”

According to the COVID-19 Genomics UK (COG-UK) Consortium—a group of public health agencies and academic institutions in the United Kingdom that sequence genomes of the COVID-19 virus—there are viruses with more than one strain, but COVID-19 is not one of them.

Will There Be More COVID-19 Variants? 

There will always be more variants because anytime COVID-19 mutates, that can be called a variant, Pekosz said. There’s just no telling what its impact will be.

Stanley H. Weiss, MD, a professor of biostatistics and epidemiology at the Rutgers School of Public Health, said that scientists aren’t sure when the next major COVID-19 variant will surface.

“We remain observers of a complex phenomenon,” Weiss told Verywell. “Until the last few months, we saw the rapid evolution of variants that then overtook others. This can certainly happen again, but we can’t yet predict when or how.”

At present, the best thing individuals can do is to stay up-to-date with the COVID-19 vaccinations to have protection against the disease.

People ages 12 or older are now eligible for the updated COVID-19 booster shots, which target both the original COVID-19 strain and Omicron subvariants BA.4 and BA5.

Health officials said the reformulated vaccines will better protect against currently circulating variants as people spend more time indoors in the fall and winter.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.