Covid Delta Variant Is Dangerous Yet Manageable, and Offers an Important Warning

The vast majority of cases, hospitalizations, and deaths caused by the Delta variant occur in unvaccinated people

Dr. Tom Frieden
4 min readJun 17, 2021
Photo: Sharon McCutcheon/Unsplash

As predicted and feared, viral variants are now causing many of the new cases of Covid disease in much of the world. The Delta variant (B.1.617.2), which appears to have spread widely in India starting last October, appears to be extremely transmissible and might cause more severe illness. The more transmissible the virus, the more people will get sick — and more people will die.

The Delta variant is at least partly responsible for the recent large and deadly wave of cases that overwhelmed health care systems in India. Delta is now spreading in at least 62 countries, including the United States. Although it currently accounts for 6 percent of U.S. cases, that proportion is growing (it was just 2 percent a few weeks ago and is now doubling quickly) — and will continue growing rapidly as a proportion of all infections, particularly in areas of the country and demographic groups that have lower vaccination rates.

Delta is now the dominant strain in the UK, increasing rapidly in recent weeks and now accounting for three quarters of new cases there. It has forced a four-week pause in the UK’s reopening plans. If Delta takes hold in the United States, it could affect our reopening as well.

The good news is that people who are fully vaccinated, at least with the mRNA vaccines, are likely well-protected against the variants identified so far, including the Delta variant — particularly when it comes to severe illness. However, people who are only partially vaccinated are only partially protected. One dose of Pfizer vaccine provides 33 percent protection against developing symptomatic Covid disease caused by the Delta variant, compared to 88 percent effectiveness after both doses.

More research is needed to confirm the effectiveness of specific vaccines against specific variants. However, all studies done so far reinforce the importance for everyone who can be vaccinated to receive all recommended vaccine doses as soon as possible. This advice covers the single-shot Johnson & Johnson vaccine as well as both doses of the Pfizer and Moderna vaccines. (Other vaccines are available elsewhere in the world, but these are the only three authorized for use in the United States.) The recent announcement from Novavax suggests that another highly effective vaccine will soon be available; because the U.S. already has three effective and approved vaccines, it might get authorized outside of the U.S. before it’s authorized or licensed in this country.

The vast majority of cases, hospitalizations, and deaths caused by the Delta variant in the UK occur in unvaccinated people. Previous infection with another Covid variant may not provide strong protection against reinfection with Delta; there’s still a lot we need to learn about variants and immunity.

Even as restrictions are being lifted, new guidelines only apply to people who are fully vaccinated. Those who are not yet fully vaccinated should follow CDC guidance and continue taking precautions, such as maintaining social distancing, wearing masks in indoor public spaces, and avoiding crowded locations.

Children under age 12 are not yet eligible to be vaccinated, so are still at elevated risk from Covid generally — and from the Delta variant in particular. There has been a recent increase in outbreaks and clusters involving variants at schools in the UK, and some schools in other countries are closing because of clusters. Younger children are less likely to experience severe illness, but can still transmit the virus to others, especially family members or other close contacts who are not yet vaccinated.

Children should continue to take precautions such as social distancing and wearing masks in indoor public spaces until they can be vaccinated, which will not be possible until September at the earliest. This is critical, as most U.S. schools have announced plans to reopen fully with in-person learning in the fall.

The Delta variant is a message from the virus: it’s still evolving, and could evolve even more transmissible, deadly, and vaccine-resistant strains. New variants emerge when there is uncontrolled spread of the virus, and can spread around the world rapidly, threatening people’s lives everywhere. Stopping emergence and spread of variants will save lives everywhere. To control spread, we must vaccinate as many people as quickly as possible. Expanding vaccination globally as quickly as possible will save lives and prevent the emergence of new variants.

The bottom line is that, although the Delta variant is especially dangerous, being fully vaccinated, particularly with mRNA vaccines, provides strong protection against it and other variants. Although vaccines are in short supply in much of the world, we are privileged in the United States to have enough vaccine for everyone. It’s important that we get as many people fully vaccinated as quickly as we can everywhere in the world, prevent emergence of variants, and progress toward full reopening of our economy and society.



Dr. Tom Frieden

President and CEO, Resolve to Save Lives | Former CDC Director and NYC Health Commissioner | Focused on saving lives.