COVID-19 Epidemiology and Common Questions

People working in an office, wearing masks durring a meeting because of COVID-19

Written by WorldClinic

July 15, 2021

Epidemiology

In the US, over half of all new COVID cases appear to be due to the Delta variant and that will likely continue to increase. In fact, in some areas, especially the Midwest and the northern Mountain states, it is over 80% of cases. In Europe, Delta is already predominant (Germany being a notable exception, for now) and is expected to reach over 90% of cases in most of Europe by the end of next month. In the UK, it is already over 95%. The rest of the world is at or on the way to similar levels. While cases in Hong Kong and Singapore are generally still at low absolute levels, the Delta variant is becoming the main strain. In Japan, a new surge, fueled by Delta, has led to increased restrictions and the removal of all spectators from Olympic events. Even South Korea, which had, up to now, prevented widespread outbreaks, has had to move to its highest level of social restrictions as they are recording their highest level of cases since the pandemic began. In parts of Australia, including Sydney, masks are required, people can only shop for essentials, and may not leave a 10km radius from their homes except in case of a special necessity.

While that all certainly raises everyone’s concern, the evidence is still excellent that vaccines, with the likely exception of the Chinese and Russian versions, are nearly completely protective against serious disease and death. In fact, current estimates are that 99.7% of new infections are in unvaccinated people. Even if someone who is vaccinated becomes infected, their chance of significant illness is very low and the amount of virus they carry and then shed into the environment is much lower than in unvaccinated, thus greatly reducing, although not eliminating, the chance that they can spread the virus to others. Those who are not vaccinated can become infected much more easily – statistically twice as easily due to Delta versus the original strain, including evidence of only brief casual contact resulting in infection. As we have previously mentioned, you cannot compare the current case rates to the way we viewed them earlier this year. If you are vaccinated, the rates you see are way overstating your relative risk, but if you are unvaccinated, the rates are completely understating your relative risk.

Back in the US, a clear inverse concordance is developing between overall case rates in any given area and vaccination rates. In areas of the country with lower vaccination rates, hospitalizations and deaths are again on the uptick. Most states with vaccination rates greater than around 55% fully vaccinated are holding steady, if not decreasing hospitalizations and deaths.

Common Questions

So now, assuming you are vaccinated, what are key considerations for how you live your life?

  • In most environments, if you are vaccinated, with what we currently know, the risk calculus says that masking does not significantly reduce your absolute risk and does not significantly increase the risk that you could unknowingly transmit the infection to those around you.

What about vaccinated workers becoming infected and carrying the infection back home to children or other at-risk people?

  • While the data is not completely clear for the Delta variant yet, the indications are that this would be very unlikely because vaccinated people are very unlikely to get infected, and even if they get infected, they are not efficient transmitters of the disease to others, including children. Additionally, even if infected, children are far less likely to become ill. Looking at the worst possible outcome, the number of children in the US who have died from COVID is very similar to the number of kids that die from Influenza during flu season, and that is even when looking at a population where many kids are vaccinated against flu versus virtually none vaccinated against COVID.
  • For this reason, once fully vaccinated, COVID concerns are not a reason to stay out of work, and the benefit of wearing a mask in the workplace if vaccinated appears to be minimal (although I do not recommend changing existing mask policies, at least for the next couple of weeks, while we get a more complete understanding of the Delta variant).

What about travel?

  • Travel is safe. Airliners have always been fairly safe because of the nature of their ventilation systems, but once vaccinated, the risks of all of the other parts of travel are also minimal. We still recommend caution in places like crowded bars and clubs as the risk of a large dose of COVID virus is higher in these environments and even the best vaccine can be overwhelmed by a huge dose of the infectious agent.
  • Even though travel for vaccinated people is safe, that does not mean it is without administrative risk. Rules and policies regarding travel, international borders, and what are allowable activities at destinations are changing again on a daily basis. If you do travel, keep a very close eye on these issues and be ready to adjust plans on a last-minute basis. Because this new variant does infect vaccinated people at a higher rate, even though getting sick is rare if you are the unlucky one who does get infected, travel testing policies will likely pick it up, so have a plan in place in case you are stuck at your destination for the 10 day isolation period.

What about attending events?

  • There is currently a large spike in cases in Finland that is directly traceable to the European Soccer championships which were open to spectators over the last couple of weeks. Essentially all of these cases were unvaccinated. The data is confirming that even in events with known transmission, those who were vaccinated appear to have been protected. There is inevitably a very small risk of infection for vaccinated, but, again, that risk is very small.
  • Considering children, with some of the data about the infectiousness of Delta strain, simply wearing a mask may not provide the same degree of protection for them as with the original strain. While children have a low likelihood of significant illness if they do catch COVID, the risk of significant or long-term effects is non-zero, so it is a careful assessment of the risk/benefit is needed and will most often tilt towards putting off attendance at crowded events by non-vaccinated children. Most outdoor events should be fine, but crowded indoor events might be worthy of rethinking.

What about the upcoming school year?

  • Delta is causing a re-look at data regarding activities that are primarily comprised of kids, including school. From extensive data from schools that were in-person last year, we conclusively know that with reasonable mitigation measures, transmission between children is low. Most school-based transmissions were adults to children, not children to children, or children to adults. And the younger the population, the more this appeared to be true. Daycare settings, for example, had very low transmission rates even though these babies and toddlers did not wear masks. Delta is causing a relook at this with new data, but so far no red flags. This is an area to keep a watch on given the increased infectiousness of Delta.

 

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