COVID-19 Epidemiology, Vaccine Statistics, and Q&A

People working in an office during COVID-19, wearing masks.

February 18, 2021


In the United States, individual case counts have seen their lowest number over the previous two days since the middle of October 4 months ago, with a comparable new low in the seven-day average. In fact, the United States overall, is below the 25 cases per hundred thousand threshold, above which represent uncontrolled widespread community transmission. 35 of 50 states are below this level, and of the remaining 15, all except New Hampshire and Mississippi have seen double-digit decreases in the number of cases over the past week. Unfortunately, only two cases, Oregon and Hawaii, are at or below the level of 10 cases per hundred thousand, which represents sporadic transmission. Deaths and Hospitalizations are also down although not by the same degree, this is not unexpected as both are trailing indicators by about a week and two weeks respectively.

In Europe, cases have been on a downward trajectory since the first week of the new year, but in total down only by about 20% from the New Year peak. The actual case rate in Europe is still lower than the United States at about 14 cases per hundred thousand versus the 25 cases per hundred thousand per day. On a country-by-country basis, the rates are still extremely variable, with some countries still well in excess of 50 cases per hundred thousand per day while others are in the low single digits. Since January 1st, the United Kingdom has seen an 80% drop in cases with the average national rate now under 20 cases per hundred thousand per day. But remember the UK still remains very tightly locked down, but with these numbers, the government is talking about the possibility of beginning to slowly reopen the economy while still keeping a close watch on the potential for an increase in case numbers.

In Asia, Japan continues to hover right around the nearly negligible level of 1 case per hundred thousand per day and they’ve announced that they will begin initiating a vaccination program this coming Monday utilizing the Astra-Zeneca Vaccine. Much of the drive for vaccination, in this traditionally vaccine-adverse country, is due to the desire to show the world that they are prepared for the Olympic games scheduled in July. Cases in Singapore and Hong Kong continue to be almost Zero as well as very low incidence in Australia and New Zealand.

Vaccine Statistics

In the United States, about 12% of the population have had at least one dose of the Pfizer-BioNTech or the Moderna Vaccines and the vaccination rate has increased from just over a million a day one month ago to 1.7 million per day most recently. Additionally, the White House announced that they will be increasing vaccinations by 23% beginning this Monday. The program to utilize neighborhood pharmacies for vaccinations had a successful first test week and the government announced that the direct to pharmacy program was increasing from 1 million to 2 million vaccinations per week.

Only three major countries in the world have vaccine rates that are exceeding that of the united states, including the UK which has immunized about 16% of its population with at least one dose, Israel which has immunized nearly half of its population, and the United Arab Emirates with is about one third.


How many days after receiving the first dose of the Moderna or Pfizer vaccine does it take to develop immunity to COVID-19, and how strong is that immunity prior to the second dose?

  • There is some evidence that very good immunity is developed by 14 days after the first dose, but no one is sure of the durability. This immunity is why some countries are delaying the second dose, but the lack of evidence on durability is why most are not.

When will a vaccine be available for young children between 5 and 10 years old? Are they doing trials with children this age yet?

  • Current trials (at least in the US) are going down to age 12. Pfizer has filled their trial and would be expected to have results over the summer, although they have not provided any projections. Moderna is having trouble getting enough volunteers. Children younger than 12 are not being studied yet.

If a person has had COVID-19 and has antibodies, should they get vaccinated?

  • Yes! The Advisory Committee on Immunization Practices has said that until/unless we have better information on the durability of natural infection antibodies, vaccination is important to maximize the chance of longer-term immunity. This could change with more data, but so far, the position is very clear.

Once you have received both doses of either the Pfizer or Moderna vaccine, even though they are each 94 – 95% effective in preventing disease, can you still be a carrier of COVID-19?

  • Generally speaking, probably not, but we don’t know for sure. This is the reason why guidance about behaviors and responses to exposures have not changed. Studies to assess this are ongoing.

After receiving the vaccine, will we have to get vaccines year over year like the flu shot?

  • There is not enough data on this yet. Two things may drive a requirement for booster shots:
    1. The durability of immunity (Even though antibodies may go down, you may still have plenty of cellular immunity (B cells). Early data for this looks like immunity lasts at least a couple of years, but it’s too early to be sure.
    2. It’s fairly easy to adjust the vaccine to account for the variants, but that means that you would have to get another shot (most likely a single dose).

What precautions should we take with the new COVID-19 variant from the UK that spreads faster? What does “spread faster” exactly mean?

  • The UK variant has been variously reported as being 35-50% more contagious because part of the spike protein that latches on to cells is more effective at binding to cells. For example, if you are in a tight poorly ventilated office space with 100 people and someone in that room had active COVID-19, you may expect that around 20 people might become infected. With the exact same conditions and the UK strain, estimates are that 27 to 30 would become infected. You should continue all mitigation measures for the new variants as the original.

What are the differences between the publicly available vaccines?

  • There are two main vaccine types:
    1. mRNA-based vaccines use a nanoparticle to get into cells in the body and once inside, the mRNA tells the cell to make copies of just one part of the outside of the virus. This part of the virus is not anywhere close to anything that would be infectious, but it is enough that the body sees it and makes antibodies against it. The current mRNA vaccines are from Pfizer/BioNtech and Moderna.
    2. Adenovirus-based vaccines use a weakened virus to literally infect cells in the body. The virus carries DNA that the cell incorporates into the nucleus of the cell, which then makes the mRNA, which then goes back into the cell body where it tells the protein manufacturing components to make the same spike protein as above. Current Adenovirus-based vaccines include AstraZeneca, Johnson & Johnson, and Sputnik V.

What are the long-term effects after recovering from COVID-19?

  • COVID-19 is essentially a vascular inflammation disease, and like any inflammation, it can take several weeks to fully recover. Vascular issues can develop during recovery (DVTs, clots, etc.), but this appears to be different than “long haulers”.

When can we be inside with people who do not live in our household without having to wear masks?

  • “How will we know?” We’ll know when community-level rates of new infections are below about one case per 100K/day. At that point, the chance of bumping into someone infected is negligibly low.
  • “When will we know? Is harder. If it wasn’t for the new strains, we would optimistically project sometime in mid-Spring, but the new strains could throw a wrench in those plans if they do cause more rapid spread or if they are less susceptible to immunity. We’ll have a better idea of this by the middle of next month.

If you’ve contracted COVID-19 already, how soon are you able to contract it again? During this “grace” period, can you still carry the virus and pass it to other people?

  • Officially, for now, you are considered relatively immune for 90 days. There is data that supports extending that to 5 or 6 months, but beyond that, we just don’t have enough data. For natural infection immunity, within those three months, there does not appear to be any significant incidence of a carrier state, but there is not enough data after that or related to vaccine-based immunity at all.

In the case of visiting relatives, would the 15-day quarantine/isolation prior to visiting be enough to feel safe around them?

  • Safe is a relative term. This is all about risk reduction and not risk elimination. In theory, if you can keep yourself isolated for 14 days prior to the visit, your risk of a prior infection just showing itself at that point is close to 0 (but not quite 0). Add a test in there a day or two before and it moves the dial even closer to 0.

Should we wear two masks?

  • According to CDC, yes. two masks are better than one.

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