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Covid-19 cases now fall into 3 different categories

Even if the current surge in Covid-19 in the US exceeds that of Spring and Summer 2020 and only follows the devastating winter wave, it is being driven by a different mix of cases than the previous waves.

At the time, the coronavirus was new and most people didn't have immunity to it. The vaccinations were months away. As cases began to rise, experts issued strong warnings that the death toll would soon rise accordingly. You were right.

But that wave is coming as the US hits a milestone: 70 percent of the population over 18 has received at least one dose of a Covid-19 vaccine. There are still large parts of the country without robust protection, with vaccination rates lagging in the 1940s. These places are driving the current rise. Still, immunity is much more widespread now and medical care for Covid-19 is vastly improved. As a result, deaths are not rising nearly as fast as cases (so far).

That would be the hope in a more vaccinated world: even if some people are still infected, the virus is more of a temporary nuisance than a life-threatening event. The vaccinated can expect this protection even if the Delta variant kicks in, but the unvaccinated are faced alone with a more dangerous virus.

What sets this wave apart from the previous ones are the different types of Covid-19 cases we are seeing now compared to a year ago.

1) Unvaccinated people

According to health experts and the data available, they represent by far the largest proportion of new cases. As reported by German Lopez von Vox, unvaccinated people make up 90 percent – or more – of confirmed new cases in every state with case data showing vaccination status.

These people are facing a virus that has mutated to become more dangerous. Some unvaccinated people will experience mild or no symptoms. This has been true since the beginning of the pandemic. But data from the UK shows that the now prevalent Delta variant leads to more hospital admissions – and all of the available data shows that it is much more transferable than previous variants.

Because different states and regions have markedly different vaccination rates, some places are more at risk than others from rapid spread. This is what happens 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, currently the second hardest hit region, according to the New York Times tracker.

These outbreaks are fueling America's surge in cases. Mississippi ranks last for vaccinations per capita and fourth for new cases. Louisiana ranks fourth for vaccinations and first for new cases.

The increase in the number of unvaccinated people is also being driven at the municipal level. An example from San Diego:

The CDC estimates that unvaccinated people are up to eight times more likely to be infected with Covid-19 and have symptoms. They are also 25 times more likely to be hospitalized with serious symptoms and 24 times more likely to die from the infection than people who are vaccinated.

Unvaccinated people with a natural immunity due to a previous infection are unlikely to show up much in the case numbers at the moment because they have immunity and that immunity seems pretty robust to this day. However, the CDC still recommends these people get vaccinated as it is not known how long natural immunity will last.

Children are the outlier group among the unvaccinated; Children under the age of 12 are still not entitled to an injection. The FDA hopes to get the vaccine approved for these younger cohorts by winter. However, we have known for some time that children are less at risk of developing Covid-19 than adults, especially older adults.

2) Vaccinated people with symptoms

These so-called "breakthrough" infections make up a small but notable proportion of the newly reported cases. Vaccinated individuals currently account for less than 5 percent of confirmed cases in most locations, based on available state-level data.

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 become infected and show symptoms.

Immunocompromised people are their own group. Vaccines seem to be 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 – in other words, herd immunity.

"For them, vaccines are literally life-saving, but only through other people's choices," said Kumi Smith, an epidemiologist at the University of Minnesota.

Otherwise, a small number of those vaccinated will develop a breakthrough infection and feel sick. The data on this was clear. With the delta variant, it looks like this number will be larger than the previous variants. People who have been vaccinated with Covid-19 can also infect other people, according to the latest CDC study on the outbreak in Provincetown, Massachusetts.

But there is a small proportion of people who have been vaccinated who have symptoms. According to the WHO, the majority of people vaccinated with infections are still asymptomatic, even if they are infected with the Delta variant.

Different people will experience different symptoms, and some cases may experience more severe symptoms than others. We know that some groups (the elderly, people with certain pre-existing conditions, etc.) are at higher risk for serious symptoms. Fortunately, vaccination rates are highest among the population over 65.

Very few people who were vaccinated ended up in the hospital. If they are unfortunate enough for that to happen, they are still more likely to survive than they used to be in the pandemic.

Lopez cited the example of the Provincetown outbreak, which has mostly occurred in vaccinated people. He reported that before vaccination became widespread, we would have expected 90 people in that group to end up in hospital and nine of them to die. Instead, only seven people were hospitalized and no one died.

That's partly because of the vaccine and partly because healthcare providers now know a lot more about how best to treat severe Covid-19 cases. For those two reasons, deaths have not risen nearly as fast as cases in the current wave.

A data delay must be taken into account; Deaths occur later than falls. But since July 4th, new cases have been rising for a month, and the daily number of cases is now seven times what it was then. There is no comparable increase in new cases. While they're up, they haven't even doubled in the same amount of time.

An open question is how much people who have been vaccinated have to worry about Covid for a long time after their infection has subsided. Although data is currently limited, it seems to suggest that vaccines may help relieve long-term Covid symptoms.

3) Vaccinated people with no symptoms

This is probably the smallest percentage of cases reported after testing positive. But we sure miss some of them too. America's high positive testing rate (now over 10 percent) would suggest some cases are being missed. Experts have said that a positivity rate of closer to 5 percent (or less) means testing levels are reasonable; Anything about that suggests insufficient testing is being done relative to the virus spread in the community.

In any case, infected people who have no symptoms are evidence that the vaccines are working.

Routine testing will identify some of these asymptomatic cases. The gathering of New York Yankees players and coaches in May is an example of how these cases crop up. A handful of people on the team experienced symptoms, but most did not report any despite testing positive. If they hadn't been tested according to MLB's rules, they might never have known they were infected.

The risk that asymptomatically vaccinated people transmit the virus is currently one of the big open questions, several experts told me. However, there is good reason to believe that asymptomatic people are less likely to spread Covid-19 than people who feel sick.

"We see this pattern in unvaccinated people," said Tara Smith, an 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 in the pandemic, with a more complicated mix of cases than ever before. What hasn't changed, however, is that vaccines are still the best protection against the virus.

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