What do we know about COVID virus variants?

COVID variants illustration

The Delta and Omicron variants of SARS-CoV-2, the virus that causes COVID-19, have already spread around the world. As a result, we’re seeing more people being infected and hospitalized.

As infectious diseases experts, we are particularly concerned about the populations of people, including children, who have no immunity to COVID-19 because they have not yet been or cannot be vaccinated. Here are answers to common questions about variants.

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, for example, a virus like influenza, which we all have some baseline immunity to due to past infections or immunizations.

The more people who get infected with a virus, the more it circulates, which causes more infections. As more people are infected, there’s a greater chance the virus mutates and this 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. This is a particular problem with COVID-19 because vaccination rates are not high enough to provide herd immunity, so the virus is still circulating (and therefore mutating) at high rates in the community.

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. We are already seeing some variants with mutations that seem to make them more transmissible and better at escaping vaccine protection.

How do the Delta and Omicron variants, as well as other potential variants, affect vaccinated vs. unvaccinated people?

Unvaccinated adults and children are at high risk of becoming ill from one of the variants. The overwhelming majority of people in the hospital with COVID-19 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. Some people complain of ear pain, which is different from the initial coronavirus infection.

With the Omicron variant, the most common symptoms are cough, fatigue, sore throat, congestion or a runny nose. Loss of taste and smell does not appear to be as common with this variant as with prior ones.

Most importantly, very few vaccinated people are hospitalized and even fewer die from infection with the Delta or Omicron variants, especially those who have received a booster vaccination. However, as of December, there is still very little data on new variants, especially the Omicron variant, so scientists and physicians are still working to determine how effective the vaccines are at preventing infection and severe illness from Omicron.

Vaccine manufacturers are already working on updates to the mRNA vaccines that may help make future doses of the vaccines more effective against Omicron.

How are the variants affecting pregnant people?

Even before the Delta and Omicron variants appeared, the mortality in pregnant people was found to be three times higher than in non-pregnant individuals — they’re a very vulnerable population. This is of major concern because pregnant people also have a low vaccination rate. The variants are too new to be able to have data specifically regarding pregnant people, but we know they are more transmissible and are at least as pathogenic as the other SARS-CoV-2 variants that we’ve already experienced.

With infection rates on the rise, that means more virus is in the community and pregnant people are at a much higher infection risk.

We are 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. The CDC and our physicians strongly recommend that pregnant people get vaccinated and boosted as soon as they are eligible.

Are the current COVID-19 vaccines effective against variants?

The Moderna and Pfizer messenger RNA (mRNA) vaccines appear to be highly effective against hospitalizations and deaths due to infection with the existing variants, though more data is needed. The Johnson & Johnson/Janssen vaccine is much less effective against the variants. Therefore, if you received the Johnson & Johnson vaccine, a messenger RNA booster is recommended. The manufacturers of the mRNA vaccines have already announced that they are working on updating the vaccines to be even more effective against the new 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 2021, before Delta and Omicron were known SARS-CoV-2 variants, 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.

In the U.S., a county in Massachusetts tracked people who attended summertime parties. Of the fully vaccinated individuals, 79% tested positive for COVID-19, nearly all with the Delta variant. Most of them were symptomatic, but only 1% required hospitalization and no one died. That showed how quickly the variant was spreading and led to new recommendations on universal masking.

How dangerous are the variants?

It depends. Some people infected with the SARS-CoV-2 variants have few if any symptoms, especially if they’re vaccinated, while others become severely ill and die. Unvaccinated people are 10 times more likely to test positive for the COVID-19 virus and 20 times more likely to die from it, according to the CDC. Individual experiences with COVID-19 and different viral variants can depend on many different personal health and lifestyle factors.

The Omicron variant spreads more easily than the Delta variant. According to the CDC, anyone infected with the Omicron variant can spread the virus to others, even if they are vaccinated and don’t have symptoms.

It is not yet known whether Omicron, which was first detected in November 2021, will cause more or less severe illness or death than the Delta variant. While current vaccines and boosters will protect against severe illness, hospitalizations and death, the CDC warns that breakthrough infections of the Omicron variant are likely to occur.

How do we stop future variants from forming?

A virus cannot mutate if it does not replicate.

The most important way future variants can be prevented is to develop herd immunity through mass vaccination. We need to get the amount of circulating virus down. To do this, at least 80% of the entire population needs to be vaccinated. The more people who are vaccinated, the fewer people are going to be ill, which lessens the risk of the virus spreading and mutating. When people carry the virus, we get multiple strains of the virus, and that's when we're going to see a higher likelihood for a resistant variant to arise.

We need people to keep wearing masks, especially in crowded, indoor areas, and avoid crowds when possible. We also need them to continue social distancing and washing their hands. Finally, we need to prevent super-spreader events where people in the crowd may be unvaccinated by mandating proof of vaccination.

Again, vaccination is the single most important thing we can do.

Should vaccinated people be avoiding gatherings in general, like visiting family members or going to restaurants?

Even if you are vaccinated, you still can carry virus and spread virus to those who are not immune — either because they’re unvaccinated or because they cannot make an adequate immune response to the vaccine. If you know your family is all vaccinated and there is a low chance of carrying virus to at-risk people, then it's OK to visit.

Social distancing is still important when it comes to being with other people, especially if you do not know their vaccination status. It's reasonable to go to restaurants, as long as you know that they're not at full capacity and there is good ventilation. Eating outside, of course, is even better.

It’s also important to consider where you are going and what you are doing after attending a large gathering. If you're going to be around someone who is immunocompromised, and you've been to an event where you do not know the vaccination status of those attending, you must take into consideration that you can carry as much virus in your throat and mouth as someone who has not been vaccinated and has no symptoms. The concern would be that you might spread that virus to immunocompromised or unvaccinated people even though you may not yourself be ill. Remember that older adults and very young children are especially vulnerable to illness, as their immune systems are not as effective at fighting diseases.

What is a key message from all of this?

So far, our vaccines appear to be holding efficacy.

We know more people are being hospitalized with the Delta and Omicron variants, especially those who are not vaccinated. It’s frightening, but we have been lucky that death rates in those who are vaccinated are much lower than reported before the vaccines were available.

We are still seeing a lot of Delta and Omicron variant spread. Therefore, it's so important that unvaccinated people practice social distancing, wear masks, use hand hygiene and get vaccinated. Vaccination not only protects the individual, but also protects children, elderly people and those immunocompromised persons who may not have responded to the vaccine in the first place (i.e., cancer patients, persons who are on medications to suppress the immune system for autoimmune disorders, transplant recipients). We can't care about just ourselves anymore. We have to care about all of humanity.


Aniruddha Hazra, MD

Aniruddha Hazra, MD

Aniruddha Hazra, MD, is an expert on infectious diseases.

Learn more about Dr. Hazra