When will the United States reach herd immunity and what will it look like? | Health

The country may be on the road to herd immunity. This is the time when a sufficient number of people are protected from diseases that cannot spread throughout the population.

But it may take months to get there, and no one expects to feel like returning to our lives overnight before the pandemic.

According to the latest federal data, more than 66 million shots have been administered and nearly 8% of the US population is fully vaccinated. Promises from manufacturers indicate that the United States should have sufficient vaccine supply to cover everyone by June. More than a quarter of the population may already have innate immunity after a previous infection, and that number may be much higher than the official numbers indicate.

However, some new variants can threaten progress, weaken the protection provided by the vaccine, and avoid some degree of innate immunity. Vaccine hesitation can also create some limitations.

To understand how these factors will affect the future timeline of the pandemic, CNN spoke with five experts. Dr. Arturo Casadevall, Chair of Molecular Microbiology and Immunology, Johns Hopkins University. Justin Wrestler, Associate Professor of Epidemiology at Johns Hopkins University. Jessica Marati Rivera, Science Communication Leader for COVID Tracking Project. Dr. Aneesh Mehta, Of the Emory Vaccine Center; and Dr. Christopher Murray, Director of Institute for Health Metrics and Evaluation.

Their responses have been edited below for length and clarity.

There’s still a lot to learn about Covid-19. But if you need to number it, what level of herd immunity do you need to reach herd immunity against Covid-19?

Casa de Baru: I am in the 65-80% range. We all hope that this virus will reach the point where it is no different from other viruses and that enough people are immune to prevent the virus from jumping any further. With so few hosts and so few people who can jump, it’s about to break the epidemic. The number of cases is a threat, and the decline curve shows that the number of people who can jump is decreasing.

Wrestler: Community immunity is a continuum. As more immunity builds, the disease becomes easier to control. Currently, control measures such as masking and capacity limits provide some protection, which helps reduce cases. However, there are still some to reach a magic number where you can withdraw most of these measures and not worry about large outbreaks, but somewhere between two-thirds and 80%. However, additional community immunity provides real benefits even when that threshold is reached.

Marati Rivera: We really need to vaccinate at least 70% of the population. If there are no significant bottlenecks in production or delivery, it may be possible by the end of the year.

Meta: I’ve seen estimates from 65% to 95%. What I really want is to make sure it reaches at least 75%.

Malay: Respiratory viruses are so seasonal that the level of immunity required in summer is much lower than in winter. Covid isn’t as dramatic seasonal as other respiratory viruses, but as we’ve learned, it’s still. Set the summer herd immunity threshold to 65% and the winter herd immunity threshold to 85%.

People who are already infected with Covid-19 may have innate immunity after infection. Can those people be counted towards herd immunity?

Casa de Baru: Okay. Very few people are known to be re-infected. Certainly there are some cases, which are documented.But even though the virus is still floating, people never get sick again and it really encourages me

Wrestler: In the short term, in the next 6 months or so, I count all infected and most vaccinated people as immune. It can be a reinfection, but most often the first infection causes a fairly mild illness.

Marati Rivera: No. Herd immunity can only be discussed in the context of mass vaccination. I’m on the more conservative side and I’m very hesitant to claim that innate immunity is making a meaningful difference in these numbers.

Meta: Perhaps. Many infectious diseases occur in the United States, but they are spreading over time. It is difficult to know exactly how many people have been infected, and certain people seem to have lost immunity shortly after infection. The goal is to protect the population through vaccination.

Malay: I usually say yes, but some evidence of the first variants found in South Africa question it. Also, everything we know about the decline of innate immunity is purely speculative.

New variants can threaten the level of protection, both in terms of vaccine efficacy and potential reinfection. To what extent does this threat affect the measure of herd immunity progress?

Casa de Baru: Variants are a major threat in the future. They can make things go crazy, but I emphasize the possibility. We know that variants exist, but there are still few documented cases of reinfection. It suggests to me that the mutant does not evade immune defense. The most encouraging thing for me is how quickly the curve is descending. I’m hoping to crash the curve before the variant becomes a threat.

Wrestler: There are several variants that seem to escape that immunity and change the equation. In a fully susceptible population, the average person with the original strain spreads the virus to three people, so two people need to be immune to begin to reduce the spread. However, in some variants, the average person can spread the disease to about five people, so four people are needed to get immunity to control the spread.

Marati Rivera: The conversation about the variant should really be about infection prevention. Keeping the transmission low allows you to keep the variant low. As the vaccine goes on sale, one of the many reasons we are still wearing masks and continuing to implement mitigation strategies is to buy time.

Meta: I think the vaccine provides excellent immunity to most of the variants out there, but those that are capable of avoiding it and can change the level of protection, especially the first identified subspecies in South Africa. There are seeds. That is why it is so important to get vaccinated as soon as possible. The sooner a higher level of protection is reached in the community, the less likely it is that new variants will spread and be developed.

Malay: If these variants spread, there is no clear route to herd immunity. It’s also a very difficult business to try to predict at what pace they will spread. However, the number of cases is declining rapidly, perhaps even more than we expected.

Some studies still show a significant amount of vaccine hesitation. How does this affect the path to herd immunity?

Casa de Baru: The number of cases is a threat, and many depend on vaccine intake up to next year. The more cases you have, the more viral replication you have and the more likely you are to get infected. If we keep going as we do now and crash the curve, the chances of a bad scenario are reduced.

Marati Rivera: The Antibacs people are loud and in the minority. They do not represent the large numbers of people in this country and I do not think they will win big when it comes to things like herd immunity. Obstacles are usually understood by non-vaccinated people, but they have won big wins in campaigns to address them.

Meta: It’s really understandable why some people in our community may hesitate about vaccines. All we have to do is to take care of them by sharing knowledge and vaccination ourselves, as well as taking precautionary measures such as wearing masks and practicing hand hygiene. , Continue to do a good job of becoming a role model.

Malay: If we can move from 25% to 10% of the unvaccinated population, herd immunity will improve significantly. Even if the variant isn’t as bad as we fear, it will be pretty close and vaccination across the turning point will make a big difference.

What is your earnings? In general, when can you expect it to return to normal?

Casa de Baru: No one in this world can tell you what percentage of protection is needed or by when it will happen. My internal organs are positive and I think 2021 will be a better year than 2020. Assuming there are no variants to force a new blockade, I think it will look different later this year. You may lift the limit in the fall, or if the curve continues to drop and the curve goes down, you may lift the limit a little earlier.

Wrestler: When you reach a very small number of new cases, it will be a sign that things can go well. When retreating control measures, you should do it slowly and carefully and be aware of recurrence. The fact of the matter is that we need to accept the fact that we live forever with this virus, so some of this comes down to deciding what is normal. It comes back many times like the flu, but that doesn’t mean it’s always a tragedy.

Marati Rivera: Immunizing 70% of the population will be an absolute game changer for us in that we will return to what we can do as we did before Covid. I’m optimistic that this fall will look very different, and I hope it means something like traveling and unmasked socializing with loved ones. If you keep the trend down, you’re on your way to getting there.

Meta: Thanksgiving is my favorite holiday and the whole family gathers at my mother’s house. My hope is to happen before Thanksgiving, both personally and professionally.

Malay: I think it will be a really quiet summer. But whether it will come back is an open question, and probably not answered until December. The combination of the two powerful forces of seasonality and the magnitude of vaccination makes things go down fairly steadily, but we have to wait.