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Even though the current wave of Covid-19 in the United States overtakes those of spring and summer 2020, following only the devastating wave of winter, it is driven by a different mix of cases than previous waves.
At the time, the coronavirus was still new and most people were not immune to it. The vaccines were still months away. When cases began to rise, experts issued dire warnings that deaths would soon rise as a result. They were right.
But this wave comes as the United States takes an important step: 70% of the population over 18 has received at least one dose of a Covid vaccine. There are still large pockets of the country without robust protection, with vaccination rates lagging behind in the 1940s. These places are the source of the current surge. Yet immunity is much more prevalent now and medical care for Covid is much improved. As a result, deaths are not increasing (so far) at about the same rate as cases.
That would be the hope in a more vaccinated world: Even though some people are still infected, the virus is more likely to be a temporary annoyance than a life-threatening event. Vaccinees can expect this protection even if the delta variant sets in, but the unvaccinated alone face a more dangerous virus.
What sets this wave apart from those that preceded it are the different types of Covid cases we are seeing now, compared to a year ago.
1. Unvaccinated people
They represent by far the largest share of new cases, according to public health experts and available data. As Vox’s German Lopez reported, unvaccinated people account for 90% of new confirmed cases – or more – in each state with case data indicating vaccination status.
These people are faced with a virus that has mutated to become more dangerous. Some unvaccinated people will experience mild symptoms or even no symptoms at all. This has been true since the start of the pandemic. But data from the UK indicates that the now dominant delta variant is leading to more hospitalizations – and all available data shows that it is much more transmissible than previous variants.
With different states and regions experiencing surprisingly different vaccination rates, some places are at higher risk than others for rapid spread. This plays out in the case data. The South, which has some of the lowest vaccination rates in the country, has twice as many new cases per capita as the West, the second hardest-hit region right now, according to the New York Times tracker.
These epidemics are behind the increase in the number of cases in the United States. Mississippi ranks last for per capita vaccinations and fourth for new cases. Louisiana is fourth for vaccinations and first for new cases.
At the municipal level, the rise in cases is also driven by unvaccinated people. An example, from San Diego:
The CDC has estimated that unvaccinated people are up to eight times more likely to be infected with Covid-19 and show symptoms. They are also 25 times more likely to be hospitalized with severe symptoms and 24 times more likely to die, compared to people who have been vaccinated.
Unvaccinated people with natural immunity due to a previous infection are probably not showing up much in the number of cases right now because they have immunity, and it seems pretty robust so far. The CDC still recommends that these people get the vaccine because it is not known how long the natural immunity will last.
Children are the outlier group among the unvaccinated; children under 12 are still not eligible to receive an injection. The FDA hopes to approve the vaccine for these younger cohorts by winter. However, we have known for some time that children appear to be less at risk of contracting serious illness from Covid-19 than adults, especially the elderly.
2. Vaccinated people showing symptoms
These so-called “revolutionary” infections represent a small but significant proportion of new cases. According to data available at the state level, those vaccinated currently represent less than 5% of confirmed cases in most places.
There are a few subgroups here. There are people with just one dose who have less protection than people with two and are therefore more likely to get infected and show symptoms.
People who are immunocompromised are their own group. Vaccines seem less effective for them. In order for people in this group to be truly protected, the virus would have to be suppressed through widespread vaccination – herd immunity, in other words.
“For them, vaccines literally save lives, but only through the decisions of others,” Kumi Smith, an epidemiologist at the University of Minnesota, told me.
Otherwise, a small number of people vaccinated will experience an active infection and feel ill. The data was clear on this. With the delta variant, it looks like this number is going to be larger than it was with the previous variants. People vaccinated with Covid can infect others as well, as the recent CDC study of the Provincetown, Massachusetts outbreak shows.
But there is a small portion of those vaccinated who show symptoms. WHO has said that a majority of people vaccinated are still asymptomatic, even if they are infected with the delta variant.
Different people will experience different symptoms, and some cases may seem more serious than others. We know that certain groups (the elderly, people with certain pre-existing conditions, etc.) are more at risk of developing severe symptoms. Fortunately, vaccination rates are the highest among people over 65.
Very few vaccinated people ended up in the hospital. If they are unlucky for that to happen, they are even more likely to survive than at the start of the pandemic.
Lopez gave the example of the Provincetown outbreak, which largely occurred among those vaccinated. As he reported, before vaccinations were widespread, we would have expected 90 people in this group to end up in hospital and nine of them to die. Instead, only seven people were hospitalized and no one died.
This is partly because of the vaccine and partly because healthcare providers now know a lot more about how best to treat severe cases of Covid. For these two reasons, deaths have not increased as quickly as cases in the current wave.
There is a data mismatch to consider; deaths appear later than cases. But new cases have been increasing for a month since July 4, and the number of daily cases is now seven times what it was then. There was no comparable increase in new deaths. While they are on the rise, they haven’t even doubled over the same period.
One open question is how worried vaccinated people should be about Covid long after their infection is gone. Although the data is currently limited, it seems to suggest that the vaccines help alleviate the long symptoms of Covid.
3. People vaccinated without symptoms
This is probably the smallest proportion of cases. Surely we miss some of them too. The high positive test rate in the United States (over 10 percent now) would suggest there are quite a few missed cases. Experts have said that a positivity rate closer to 5% (or less) means that the test levels are adequate; all of the above indicates that an insufficient number of tests are performed for the amount of virus that is spreading in the community.
Either way, infected people who have no symptoms are evidence of the effectiveness of vaccines.
Some of these asymptomatic cases are detected by routine testing. The regrouping among New York Yankees players and coaches in May is one example of how these cases arise. A handful of people on the team experienced symptoms, but most reported none despite testing positive. If they hadn’t been tested via MLB rules, they might never have even known they were infected.
The risk of asymptomatic vaccinated people transmitting the virus is currently one of the big open questions, several experts told me. There is, however, good reason to believe that asymptomatic people are less likely to spread Covid than people who feel sick.
“We see this pattern in unvaccinated people,” said Tara Smith, epidemiologist at Kent State University, in an email. “People who are completely asymptomatic are less likely to spread than those who eventually develop symptoms. “
We have entered a new phase of the pandemic, with a more complicated mix of cases than what we have seen before. But what hasn’t changed is that vaccines still offer the best protection against the virus.
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