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Michigan and other states that experienced springtime Covid-19 surges or faced worrisome transmission trends appear to have turned a corner, with drops in new cases in recent days as vaccines reach more people.

After hovering at stubbornly high levels or increasing over the past two months, average daily cases in Massachusetts, Minnesota, New Jersey, Illinois, and other states in the Midwest and Northeast have started to fall, providing a breath of relief that the communities are past their most recent peaks. Crucially, new infections in Michigan — which experienced the worst of the spring spikes, with some of its highest Covid-19 levels of the entire pandemic occurring in recent weeks — have started declining, with hospitalizations also starting to tick down.

Experts are cautious that the progress has just begun and needs to be sustained if the states want to actually achieve low levels of transmission. But they’re heartened that it appears vaccines are increasingly not just protecting individuals from Covid-19, but are starting to have broader benefits for communities.

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“April’s been a bad month,” said Preeti Malani, an infectious disease physician at the University of Michigan. “There are hospitals across the state overwhelmed with patients. And because staff are sick, they’ve been having trouble with staffing their hospitals.” Different parts of the state remain under different levels of pressure, but now, with a big increase in vaccine availability in the past month, Malani said, “I’m optimistic about the direction we’re headed.”

At the national level, the country’s average daily infection count has also started to come down, from more than 70,000 in the middle of April to closer to 60,000 now. But summarizing the U.S. Covid-19 epidemic from that frame obscures how much variability there is. After experiencing a horrific surge over the winter, California now has one of the lowest rates of infections in the country, while cases in Puerto Rico have increased over the past month.

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“We remain in a complicated stage,” Rochelle Walensky, the director of the Centers for Disease Control and Prevention, said at a briefing Monday. “On the one hand, more people in the United States are being vaccinated every single day at an accelerated pace. On the other hand, cases and hospitalizations are increasing in some areas of the country, and cases among young people who have not yet been vaccinated are also increasing.”

The progress in the United States stands in stark contrast to most of the rest of the world, which lacks anything close to the vaccine supply this country has. Persistently high cases in Europe and the Americas and huge spikes in Asia have driven global case counts to among the highest levels of the whole pandemic.

Trends can also be moving in the right direction when, in raw numbers, infections are still high. Cases may be coming down in Michigan, but they’re still higher than they were there at just about at any other point in the pandemic. National case counts in the 60,000 range as opposed to the, say, 20,000 range mean that many more people will suffer severe outcomes from the coronavirus. And while death counts have dropped dramatically from the more than 3,000 people taken daily in the United States in stretches of January and February, the progress has been stalled at more than 700 deaths per day. The hope is that if case counts continue to fall over the coming weeks, deaths will follow in turn.

Already, the rollout of vaccines has dramatically changed the dynamics of the U.S. epidemic. Hospitalization and death rates among older adults — the population with the highest immunization coverage — have plummeted, while hospitalizations among younger adults have also started to come down more recently. Whereas for the first year of the pandemic hospitalizations and deaths would follow case counts in predictable patterns, experts now speak of vaccines “decoupling” those metrics because they are so powerfully protective against the worst outcomes of the disease.

But the shots aren’t just protecting individuals. Increasing evidence shows that they take a substantial bite out of transmission once they’re given to a certain swath of the population, as countries like Israel that have vaccinated most of their populations have demonstrated. It’s not a specific threshold — it will vary place to place depending on other factors — but experts are hoping and anticipating that some places in the U.S. could be nearing that point, and drops in case counts could accelerate.

“I think that might be what’s happening in the Upper Midwest,” said infectious disease physician Monica Gandhi of UCSF.

Experts had expected that the vaccine rollout would suppress Covid-19 come this summer, to such low levels that many of the activities we’ve forsaken over the past year could be done relatively safely.

But there was an intermediate hurdle: In some states, cases started rising again this spring, as politicians eased restrictions and individuals grew more relaxed. More transmissible variants of the coronavirus pushed cases up or slowed progress — most notably B.1.1.7, which ignited major outbreaks in the United Kingdom (where it first emerged) and then in other European countries. Some recent transmission in New York and New Jersey also seems to have been driven by another variant, B.1.526.

The declining case counts in Michigan and other states suggest we may be back on track.

“I’m hopeful for that,” epidemiologist Stephen Kissler of Harvard’s T.H. Chan School of Public Health said about the U.S. dodging the full brunt of B.1.1.7. “I’m cautiously optimistic.”

One reason is that the weather got warmer, which appears to have an impact on transmission both for behavioral reasons (people spend more time outdoors) and perhaps for biological ones (many respiratory viruses lose some of their transmission efficiency in hotter, more humid temperatures). B.1.1.7-fueled spikes in the U.K. and Europe were exacerbated because they occurred over the colder months, for example.

The U.S. also had a big wall of natural immunity blunting just how widely the virus could spread this spring. Experts estimate that more than 100 million people in the country have recovered from an infection — the vast majority of whom remain protected against reinfection for now.

And then, of course, vaccines. More than half of adults in the U.S. have received at least one dose of a vaccine, and a full third of adults are fully vaccinated.

The factors that spur outbreaks or slow them — the weather, the number of susceptible people, the virus itself, the precautions people take — can compound or counteract each other, and the plateaued national case count in recent weeks is a reflection of an almost even tug-of-war. But it appears that the balance in more places appears to be tilting toward declines.

“Our optimism that the country as a whole has reached a clear turning point is further reinforced,” modelers at Children’s Hospital of Philadelphia’s PolicyLab wrote in their latest update on Wednesday. “This is great news for a Covid-weary nation, but we are mindful that the rates of improvement for some areas will be quicker than others.”

For all the progress achieved with vaccines, the U.S. is reaching the point where supply is outpacing demand in a growing number of communities. The average number of daily vaccines administered reached a peak of nearly 3.2 million earlier this month, but has since fallen to 2.8 million, even as all people 16 and up became eligible for the shots. It’s a matter of both access and hesitancy, and health officials at every level will increasingly have to reach people where they are or assuage their concerns to get more shots in arms. The University of Michigan’s Malani, for example, raised the concern that teens and young adults could drive outbreaks if they’re not incentivized to get vaccinated.

Experts still foresee a summer when vacations and barbecues return. The coronavirus won’t be gone from the United States, but at what level it circulates —  and how much damage it inflicts — in large part depends on how many people in each area remain unvaccinated. (Most children still won’t be vaccinated this summer, but experts say that high levels of vaccine coverage among adults and lower transmission rates generally will reduce spread among children as well. Children overall are far less vulnerable to severe outcomes from Covid-19 than older adults, and appear to transmit the virus at lower levels.)

One trend experts will be keeping an eye on this summer is if there are echoes of summer 2020. While the warmer weather gives states in the northern part of the country some breathing room, last summer brought large outbreaks in places like Texas and Florida, where summer temperatures drive people into air-conditioned indoors. If there are large pockets of people who remain susceptible to Covid-19 in those places, they could potentially see a repeat increase in cases — if on a significantly smaller scale — this summer.

  • The seasonality folks are gleefully showing the amazingly exact parallels between spring this year and last year. They also overlay Hope-Simpson from 100 years ago, which predicted the small spring surge and subsequent decline.

    Along those lines, their question is how big the southern surge will be in a couple of months. It will be important not to blame that surge purely on the slower rates of vax there, because it is so clearly predicted by the historic data.

  • The virus has been proven to be air-borne. If people would simply ALL wear masks, and wear them properly (it is hilarious to see dumb half-A****d attempts) 80% of the spread would not happen. That – ane EVERYONE needs to get vaccinated. Otherwise life in America will simply never return to normal.
    Because of that, it is very important that Americans get vaccinated before vaccines leave the country.

  • “(many respiratory viruses lose some of their transmission efficiency in hotter, more humid temperatures).” ??? Covid numbers in Southern states clearly debunk this. But if you believe in this myth then don’t worry about climate change either.
    “B.1.1.7-fueled spikes in the U.K. and Europe were exacerbated because they occurred over the colder months, for example.” ??? It was human behaviour and indoor actitivities that caused the increase.
    The ridiculous spring peak was simply / stupidly caused by 1 thing : idiotic spring break partiers. That same gang needs to get rattled to get vaccinated. If they are oblivious to increasing number of ever younger people succumbing, then maybe the virus already got to their brains. Sorry – the only good thing in this article is that vaccinations are scoring results.

  • So what is so bad or unconscionable for the US to wait until 2/3 of its adult population have been fully vaccinated thus enhancing our herd immunity. Then restrict any travel to any surging countries bybzyzs cutuzens, prohibit any travelers coming from the same countries, then finally consider exporting our vaccines?

    Take care of our own people first and foremost right? Isn’t that the most fundamental, cherished, and agreed by most as the definition and the fundamental tenet of nationalism?

  • Apropos of Steve White’s comment below, it’s always instructive to keep in mind in insights of that great moral philosopher, Yogi Berra.

    It’s hard to make predictions, especially about the future.

    However, the progress of any epidemic can be understood as right shifting quasi-Gaussian curve, with a narrow left tail, a skewed mean of a varying quantity/height, with a peak number, and a long and declining right tail. There will be bumps and spikes on the way down, but the trend is down.

    This virus, like all others, should follow that curve form. But the key question is this: how long, and how high, will that right tail be?

    By the way, this is not a prediction. It’s the way nature operates.

    For some reason, some people believe that variants MAY somehow make that right tail morph into and entirely NEW quasi-Gaussian distribution. I would bet — and yes, it’s a bet — that this outcome is low probability. Unless, of course, this was a gain-of-function man made virus and it was constructed to enhance that possibility, or constructed in a way that may unintentionally lead to that outcome.

    Once again, and I’ve said this on a number of my STAT comments, addressing epidemics is an exercise in risk management with incomplete information. Unfortunately, our policy is driven by highly risk averse public health officials, couching all their statements in the conditional mood, and not by individuals who understand important policy tradeoffs.

    Simply put, kids need to get back to school, masks need to come off, lockdowns and business interruptions have to come to an end. And, frankly, sooner rather than later.

    • Your comment is by far one of the best responses I have read in recent months. Back to normalcy is paramount! I wish more Americans had your brain power.

  • I appreciate the article but I think the importance of the variants in the current and future course of the pandemic is not being adequately emphasized.
    Perhaps it is due to mask use and closings – but the graph of the epidemic in Michigan is completely different than the graph in California. This is true for several other states.
    California did not relax rules for the holidays – we had a huge surge beginning in November and accelerating through New Years Eve – maxing out a short time later – followed the holidays perfectly – Michigan – No, not even close.
    Detailed info. on actual compliance with social distancing might show it was the most important factor, but I am very skeptical. I think it was the prevalence of variants.

    And, as far as vaccination rates effecting disease rates now – yes, they make a big difference – unless a vaccine escaping variant is driving an outbreak. Hopefully, the vaccines will work well enough that it does not happen.

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