The Delta variant of SARS-CoV-2, the virus that causes COVID-19, has already spread to more than 100 countries. As a result, we’re seeing more children being infected and hospitalized with the Delta variant compared to original strains of the virus.
“I am particularly concerned about the populations of people, including children, who have no immunity to COVID-19 because they have not yet been vaccinated,” said Prof. Kathleen Mullane, an infectious diseases expert at UChicago Medicine.
In the Q&A below, Mullane provides answers to common questions about variants—including an explanation of how viruses mutate, and why widespread vaccination remains our best defense against COVID-19.
What is a variant, and where do variants come from?
A variant is a group of viruses that share an inherited set of distinctive mutations in their genetic code.
RNA viruses mutate; it's what they do. When a virus replicates or makes copies of itself, errors can occur in the instructions (the RNA template) as they're being read. In other words, the virus has a misprint. All coronaviruses have an enzyme called an error-correcting polymerase, which removes that incorrect insertion (misprint) in the RNA and replaces it with a "better one." The better one, however, is not always perfect.
Sometimes, the mutation can be terminal, meaning the virus can't replicate anymore and dies off. Other times, there’s no significant change in the virulence of the virus and its characteristics remain unchanged. Sometimes, however, the mutation causes a significant change in the genome, making a virus more transmissible and infectious.
How quickly does a virus mutate?
Some viruses, like influenza, can mutate quickly, while others change more slowly. SARS-CoV-2 mutates two to six times more slowly than influenza. What has made SARS-CoV-2 so troublesome is that the general population hasn’t had immunity to this coronavirus sub-genus. That means many more people are being infected with it than we would see with influenza, which is a virus we all have some baseline immunity to due to past infections or immunizations.
The more people are infected with a virus, the more it circulates, which causes more infections. As more people are infected, there’s a greater chance it mutates and leads to the circulation of multiple strains. As more strains circulate, there is a greater chance for recombination between strains. That’s when new variants occur.
We don't know whether these variants are going to be more or less aggressive in the future, but we are very concerned we could see the development of viruses that are more aggressive and that our vaccines ultimately may not be able to protect us.
How do the Delta variant and potential other variants affect vaccinated vs. unvaccinated people?
Unvaccinated people are at high risk of becoming ill with the Delta variant. When we look at hospitalizations right now, between 90% and 97% of people who are in the hospital have the SARS-CoV-2 Delta variant and are unvaccinated.
For those who are vaccinated, a Delta variant infection generally feels like a mild upper respiratory illness with a cough, headache, sore throat and some muscle aches that are short lasting. Very few people end up losing their sense of smell or taste. One unusual finding that we've seen is there are more people complaining of ear pain, which is different from the initial coronavirus infection. Most importantly, very few vaccinated people are hospitalized and even fewer patients die from infection with the Delta variant.
How are the variants affecting pregnant people?
Even before the Delta variant appeared, the mortality in pregnant people was found to be three times higher than in non-pregnant individuals—they’re a very vulnerable population. Delta is too new to be able to have data specifically regarding pregnant people, but we know it is more transmissible and is at least as pathogenic as the other SARS-CoV-2 variants that we’ve already experienced.
Many more people are getting infected with the Delta variant, which means more virus is in the community. That puts pregnant people at a much higher infection risk.
We are also now seeing babies infected, too. Infants don’t develop an immune system until they’re about 6 months old. We know a vaccinated person who gives birth passes some immune protection to their baby, which is another reason vaccination is so important, especially among those who are pregnant.
Are the current COVID-19 vaccines effective against variants?
The efficacy of our current vaccines is variable. The messenger RNA (mRNA) and the Johnson & Johnson/Janssen vaccines appear to be effective against hospitalizations and deaths due to infection with the existing variants. The Sinovac vaccine and some other adenovirus-based vaccines produced outside the U.S. don't appear to be as effective as the mRNA vaccines. Worldwide, physician-scientists are looking at giving patients who were vaccinated with Sinovac or those other vaccines a dose of mRNA vaccine to see if that enhances their immunity.
Currently, our vaccines are effective against variants. We can look at efficacy of the mRNA vaccines in two studies that have been published: one in the United Kingdom and one in Israel. In the study done in the U.K., they showed 88% efficacy against symptomatic disease after two doses of an mRNA vaccine and 33% after a single dose. However, when they looked at hospitalizations, they reported 96% vaccine efficacy against hospitalization after two doses and 94% after one dose.
In Israel, the results were different. In early June, before Delta really became the predominant circulating SARS-CoV-2 variant, they reported about a 64% vaccine efficacy in preventing infection, or symptomatic disease. However, by the end of June and the beginning of July, the vaccine was only 39% effective against the Delta strain. When they looked at serious illness, the vaccine was 93% effective against serious illness or hospitalization, and by the end of July vaccine efficacy was 91% against serious illness and had fallen to 88% against hospitalization.
The AstraZeneca vaccine was reported to have 60% vaccine efficacy against symptomatic disease after two doses but only 33% after one dose. However, vaccine efficacy was 93% against hospitalizations, which is the important variable — meaning people are not getting seriously ill with COVID-19. For Johnson & Johnson, there was still good vaccine efficacy: 79% against symptomatic disease after two doses and 96% against hospitalization after two doses.