As public health officials continue to urge Americans to roll up their sleeves for COVID-19 vaccines, coronavirus infections have been on the rise in areas where vaccination rates remain low. That's due in no small part to the Delta variant, which has become the dominant strain in the United States.
Delta has taken over in an alarmingly short time. Based on genomic testing, the Centers for Disease Control and Prevention estimates that the variant first identified in India accounted for 10% of cases during the two-week period ending June 5. Four weeks later, Delta's share had swelled to nearly 52%.
And it shows little sign of stopping: Coronavirus infections that had been dramatically reduced in the United States, thanks to COVID-19 vaccinations, are on the rise once again.
Both these facts serve as a testament to the ease with which Delta spreads: It’s estimated to be 40% to 60% more transmissible than the Alpha variant from the United Kingdom, which itself was about 50% more transmissible than earlier versions of the virus. That means Delta spreads more than twice as readily as the coronavirus that initiated the global pandemic.
But what does a Delta variant actually do to those it infects? The Times spoke with two infectious disease experts — Dr. Robert Bollinger of Johns Hopkins University and Dr. Otto Yang of UCLA — about what we know so far. The interviews have been edited for length and clarity.
What sets the Delta variant apart from earlier versions of the coronavirus?
Dr. Robert Bollinger: For lack of a better term, it's a little stickier. That's why you're seeing higher transmissions and outbreaks.
Even in places like Britain and Israel, where they have a lot of people vaccinated, those who aren't vaccinated are at even higher risk of getting infected when you have a more infectious variant. So that's been the main issue.
Does the Delta variant cause different COVID-19 symptoms?
Dr. Otto Yang: It can look more like a runny nose, which is not as common previously. There are mild differences like that, but overall it's very, very similar.
The most important symptoms of course are still cough, shortness of breath and fever.
Are the symptoms more severe?
Yang: It's hard to tell, because you're dealing with a disease where the natural degree of severity is so widely variable — it ranges from completely asymptomatic to severe illness and death. The variability is so high at the baseline that you would need a really large number of people to be compared to tell.
So it's not clear if it is more deadly or not. We just don't know.
Bollinger: I think the jury's still out on that. One of the things that you have to keep in mind is the difference in symptoms could be a difference in the virus — but more likely it's a difference in the person that's infected.
What do you mean?
Bollinger: People getting infected now are a lot younger than they were with the earlier variants, because the older people are vaccinated at a much higher rate. So are some of the differences that are being reported related to the virus, or just the fact that it's younger people getting infected? I don't think we really know that yet.
Yang: Exactly. There are multiple moving parts, so it's hard to make a clear comparison.
A lot of people said COVID is becoming less and less deadly because mortality rates are going down. That’s not necessarily the case. The demographics have changed. If younger, healthier people are now the ones mostly getting infected, it's not surprising the mortality is lower. It doesn't mean the disease has changed. This means the people getting infected have changed.
Is the Delta variant more likely to cause breakthrough infections in people who are fully vaccinated?
Bollinger: We haven't seen evidence of that just yet.
Breakthrough infections can occur for a couple of different reasons. If your antibody levels decline over time, you might be susceptible to breakthrough infections. The other type of breakthrough infection scenario is where the virus itself has mutated, so that the immune response you have doesn't work as well. So those are two different potential scenarios, and both of those are being monitored.
Delta has already spun off a similar variant known as Delta-plus. Is there a chance it could spin off another, more troubling variant?
Yang: Absolutely. Mutations happen when the virus is replicating — copying itself in a person. The mutations happen as the virus makes genetic copies of itself for new viruses. The more people are infected, the more chance there is for mutations to come up.
In each person that gets infected, it's like a lottery ticket for the virus to make a new mutation that's beneficial to itself. So the more people, the more lottery tickets, basically.
What’s the takeaway for people worried about being infected with the Delta variant?
Yang: The takeaway is that we can't rely entirely on the vaccines, because they are probably not going to be as effective in preventing the virus from spreading around. We can't just jump back to "normal life." We have to realize this virus is still a threat. And we have to take reasonable precautions to protect ourselves from getting infected even if we're vaccinated.
Even though the vaccine may make it so that illness is milder and that we may be personally protected, we have to keep in mind that there are many people who aren't vaccinated who are vulnerable. There are also people in whom the vaccine doesn't work who are vulnerable.
As a society, we need to be responsible about protecting everybody.
This story originally appeared in Los Angeles Times.