The CDC designated the delta variant of the coronavirus — first identified in India — as a "variant of concern" June 15, reigniting attention on the race between vaccines and coronavirus variants.
The new classification comes amid mounting evidence that the variant spreads more easily than existing strains and causes more severe infections, the CDC said in a June 15 statement to Becker's. People infected by the delta variant may have twice the risk of hospitalization of people infected with the alpha variant first identified in the U.K., according to research released this week from Scotland. In May, the U.K.'s Scientific Advisory Group for Emergencies also said the delta variant could be up to 50 percent more transmissible than alpha, which is currently the dominant strain in the U.S., though research is still preliminary.
The delta variant now accounts for about 10 percent of COVID-19 cases in the U.S. and could become the nation's dominant strain by this fall, according to Scott Gottlieb, MD, a former FDA commissioner who now serves on Pfizer's board of directors.
The good news? Vaccines offer strong protection against this variant, underscoring the importance of maintaining vaccination efforts to prevent delta from gaining a foothold in the U.S., Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, said June 8.
The vaccines also offer varying levels of protection against the CDC's four other variants of concern.
In June 2020, the FDA said any COVID-19 vaccine candidate would have to reduce the chance of infection or severe disease by at least 50 percent to be considered for emergency use authorization. At the time, infectious disease experts, including Dr. Fauci, were hoping for COVID-19 vaccines to surpass the 50 percent efficacy mark.
"I'd like it to be 75 percent or more," Dr. Fauci said during an event in August 2020, before any vaccines were approved for use in the U.S.
All three of the COVID-19 vaccines approved in the U.S. surpassed the 50 percent guideline: Pfizer's shot demonstrated 95 percent efficacy in clinical trials, Moderna's was 94 percent effective, and Johnson & Johnson's vaccine was 66 percent effective, according to the CDC.
While those clinical trials were conducted before the emergence of these variants, emerging data is encouraging, as the vaccines still surpass the FDA's initial expectation of 50 percent protection against the newer strains.
Below is a summary of existing research about vaccine efficacy for each of the CDC's variant of concern. Variants are listed in alphabetical order.
Alpha, first detected in the U.K.: In April, this became the dominant strain in the U.S. While it's thought to be about 50 percent more transmissible than the original strain, a growing body of research has indicated the alpha variant has a minimal effect on neutralization generated by current vaccines or during previous infection.
A real-world study from Qatar, where the variant made up about 45 percent of cases by mid-March, showed Pfizer's vaccine was nearly 90 percent effective against the strain two weeks after the second dose.
Lab tests have also shown Moderna's vaccine is protective against the variant: A study from January published in the preprint server bioRxiv found no significant difference in the shot's ability to neutralize against alpha compared to earlier strains.
Beta, first detected in South Africa: This strain is about 50 percent more transmissible than earlier versions, according to the CDC. While considered the "nastiest of all variants," according to Laith Abu-Raddad, PhD, infectious disease epidemiologist at Weill Cornell Medicine-Qatar, studies have offered promising results on the vaccines' ability to prevent infection from beta.
In the same real-world Qatar study referenced above, published May 5 in The New England Journal of Medicine, researchers found Pfizer's shot was between 72 percent and 75 percent effective at preventing infection caused by the variant at least two weeks after the second dose. At the time, beta was responsible for about half of all COVID-19 cases in Qatar.
"It's not the 95 percent we were hoping for, but the 75 percent is really great," said Dr. Raddad, who is also one of the study's authors.
When it came to preventing severe disease, Pfizer's vaccine offered near-total protection against beta.
In a lab setting, researchers observed a six-fold reduction in neutralizing titers — a measure used to indicate the concentration of antibodies in the blood — produced by Moderna's shot. Despite the reduction, neutralizing titers against the strain remained above levels that are expected to be protective, the study said.
Gamma, first detected in Brazil: Early research suggests vaccines offer reduced protection from infections caused by this strain, according to the CDC. While little real-world data has been published on vaccines' efficacy against this strain, Moderna said a booster shot it's developing "should be protective" against the strain based on early clinical trial data released May 6.
A small, 20-person clinical trial from Johnson & Johnson found its vaccine stimulated 3.3 times fewer neutralizing antibodies against the gamma variant compared to the originally circulating strain. However, the single-shot vaccine prevented severe COVID-19 in 88 percent of participants in Brazil and 82 percent in South Africa, where the beta and gamma variants are prevalent.
Delta, first identified in India: Real-world data shows vaccines are highly effective against this variant. In a recent analysis of 19,543 people in Scotland, Pfizer's vaccine was 79 percent effective in preventing infection from the delta variant. Research from Public Health England suggests protection may be even higher. The study, released May 22, found Pfizer's shot was 88 percent effective against the variant two weeks after the second dose.
Finally, a separate study of 14,019 people in England found two doses of Pfizer's vaccine were 96 percent effective in preventing hospitalization from the delta variant.
Epsilon, first detected in California: Vaccines may be less effective against this variant, which is about 20 percent more transmissible than previously circulating strains, according to the CDC. The agency cited preliminary lab research published March 9 in the medical preprint server medRXiv, which found a two-fold decrease in neutralizing titers among vaccine recipients against this strain. The study was not peer-reviewed.
Newer research proves more hopeful. A research letter published April 7 in The New England Journal of Medicine found only a modestly lower value in neutralization titers against the variant after analyzing virus samples from 49 people who received either Moderna or Novavax's vaccine. Based on their findings, researchers concluded vaccines are "likely to remain effective" against the variant. Outside of this lab research, little clinical data exists about the vaccine's protection against the epsilon variant in the real-world.