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July 30, 2021

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COVID-19 Vaccines and the Delta Variant

COVID-19 Resources
On behalf of the Emerging Infectious Disease Task Force

There are mounting numbers of cases of the Delta variant across the nation. There is also new information on the effectiveness of the COVID-19 vaccines against this variant. Who is getting sick, who is getting admitted to the hospital and how effective are the vaccines?

COVID-19 Cases – What are the case numbers nationally?

The SARS-CoV-2 Delta variant has quickly replaced all other varieties of the virus globally and in the United States. The prevalence of the Delta variant here in the U.S. has been growing rapidly since early April 2021 from a few percent, to well over 90% of all cases by the last week of July 2021.

This has been accompanied with a fourth surge in COVID-19 cases and hospital admissions. We are still well below January 2020 when we saw about 260,000 new cases every day. Currently, we are averaging about 41,310 new cases per day, up by almost four times the 11,000 daily average at the beginning of June 2021, and the trend is continuing to rise sharply.

Who is getting sick and dying from the Delta variant?

The admissions and deaths during this fourth wave are almost entirely in unvaccinated or incompletely vaccinated people. The truth of the matter is clear to anyone willing to listen and look at the information. Get vaccinated.

Although some are calling this fourth wave the “wave of the unvaccinated,” the issue is deeper than that. The high numbers of unvaccinated people with the virus significantly increases the amount of virus circulating in the country. This enhances the chances that anyone – even if fully vaccinated – will be exposed to and contract the disease.

It also puts the odds fully in favor of the SARS-CoV-2 virus. With a more contagious variant to build on, it could mutate into an even more lethal form.  And that impacts all of us.

We got vaccinated, so what is the risk with the Delta variant?

The bad news is that a small proportion of people who are fully vaccinated with an mRNA vaccine, have gotten the Delta variant. A few have even been hospitalized and even fewer died.  However, the vast majority of fully vaccinated people who have these vaccine breakthrough infections, have mild cases.

Most of these vaccinated people will test positive by nasal swab Nucleic Acid Amplification Tests, so they could be contagious. Remember those tests have a high false-positive rate because they turn positive even with dead viral fragments. Dead viral fragments do not transmit the disease. On-going studies should determine how many active viral particles are shed by fully vaccinated people who have mild symptoms, and how long they shed them. This information will likely impact (and probably shorten) the recommendations for self-isolation after a vaccinated person gets a mild case of COVID-19.  But we should wait for these data to come out before changing our approach.

The most important fact here is that an mRNA vaccine keeps almost everyone from getting sick enough to be admitted to the hospital and it is rare that anyone with a COVID-19 mRNA vaccine dies of COVID.

What do the data show regarding the effectiveness of the mRNA vaccines?

A recent publication in the New England Journal of Medicine reported on the Pfizer BioNTech and AstraZeneca mRNA vaccines. They compared the effectiveness of the two vaccines with the original Wuhan variety, the previous United Kingdom Alpha variant and the current Delta variant. These data are likely to be directly applicable to the Moderna vaccine as well due to its similarity to the Pfizer vaccine. Although the AstraZeneca product is not available in the United States, we are going to cover that information as it is an mRNA viral vector vaccine, similar to the Janssen product.

What is the effectiveness of a single dose of a two-dose vaccine (Pfizer/AstraZeneca)?

Remember that for a while the United Kingdom was recommending that a single injection of the AstraZeneca vaccine be given in order to get at least some protection out to people more quickly. They hoped to provide the second dose of the AstraZeneca vaccine at a later time. Providing the second dose months later has proved quite problematic for the UK’s Public Health organization. People with only a single dose of either the Pfizer or AstraZeneca products have a low effectiveness for the Alpha variant (48.7%; [95% CI], 45.5 to 51.7).  They fared even worse with the Delta variant at (30.7%; [95%CI], 25.2 to 35.7). The numbers are similar with both the Pfizer and AstraZeneca vaccines.

What is the vaccine effectiveness for the two-dose vaccines?

With two doses (the normal recommended and studied protocol) of the Pfizer vaccine, the effectiveness increased to (93.7% [95%CI] 91.6 to 95.3) for the Alpha variant and (88.0% [95%CI], 85.3 to 90.1) for the Delta variant. This still is a clinically significant high level of protection and is consistent with previous estimations the TeamHealth Emerging Infectious Disease Task Force has covered in other videos and posts.

With the AstraZeneca vaccine, the effectiveness of two doses was (74.5% [95% CI], 68.4 to 79.4) among persons with the Alpha variant and (67.0% [95% CI], 61.3 to 71.8) among those with the Delta variant. Although less effective than the Pfizer vaccine overall, the effectiveness is well above the required 50% range, and is higher than most years of influenza vaccines.  Even in a “bad match” year, the influenza vaccines still save tens to hundreds of thousands of lives.

What about the effectiveness of the single-dose Janssen vaccine?

We haven’t forgotten the Janssen (Johnson and Johnson) single-dose COVID-19 vaccine, but there is not much information about it yet.

Using in-vitro antibody neutralization lab tests, the researchers estimate the effectiveness of the Janssen single-dose vaccine against the Delta variant to be very close to 50%. Recall that 50% effectiveness is the cut-off set by the FDA for applying for an FDA Emergency Use Authorization. Also recall that this paper is not a clinical trial, only a lab antibody neutralization test, and the paper has not yet been peer-reviewed.

Is the Janssen vaccine useful at all?

Yes, the Janssen vaccine is useful. Even with the reports of thrombosis, and neurologic problems, the rates of these complications are orders of magnitude lower than the same problems caused by COVID-19 itself.

Understand that the initial studies showed that no one given a Janssen COVID-19 vaccine, died of COVID. More people may become ill than with the other vaccines, but the initial information is that most deaths are averted. From that context, it is a very effective and useful vaccine.

What else might impact the effectiveness of the Janssen vaccine?

Some of the differences in effectiveness between the Pfizer and Moderna vaccines compared to the Janssen product is also due to when and how the studies were conducted. The Pfizer and Moderna vaccine studies were done when the prevalence of SARS-CoV-2 in populations was relatively low – between the first and second waves.

There was also only a single variant circulating at the time of the Pfizer and Moderna studies.  The Janssen product was tested during the peak of the second pandemic wave and included several variants such as the Alpha and Beta. These factors will automatically decrease the apparent effectiveness of any vaccine tested under those conditions.

What are the implications of this information?

Very few people with any COVID-19 mRNA vaccine will become ill enough to need hospitalization, and even fewer will die of the disease. And so far, this includes all the mRNA vaccines from Pfizer, Moderna, AstraZeneca, and Janssen. Those vaccinated who have serious problems typically have complicating medical conditions.

What can we do as clinicians to make things better?

To make things better and end this pandemic we need to advocate vaccination for everyone. This includes educating our patients, families, and even our colleagues in some settings. Wear your Lead with your Shoulder TeamHealth vaccine pins and start conversations.

A number of clinics and Emergency Departments have started coordinating with their parent facilities and health departments to offer the vaccines to patients directly while they are being seen.

What can we do to enhance our own protection?

To make yourself safer, use an N95 respirator even if you are fully vaccinated in your patient encounters. Use face coverings and social distancing in your outside activities, especially if your community is suffering a “hyperlocal outbreak.” This is when there is a significant spike in COVID-19 activity in a community. These communities typically have a lower than usual 20% – 30% vaccine penetration rate. Although the cases seen are mostly among unvaccinated individuals, the virus burns through these communities and the high level of viral shedding puts everyone at increased risk.

Many of the hyperlocal outbreaks are in rural or other secluded and initially semi-protected communities.  However, as we watch the statistics, we are seeing the COVID-19 admission and mortality rates begin to increase in a number of metropolitan areas as well.

Stay smart, stay safe and double down in your town with vaccines and PPE.



Tada T, Zhou H, Samanovic MI, et al. Comparison of Neutralizing Antibody Titers Elicited by mRNA and Adenoviral Vector Vaccine against SARS-CoV-2 Variants bioRxiv 2021.07.19.452771

Lopez B J, Andrews N, Gower C, et al. Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant. N Engl J Med. 2021 Jul 21. doi: 10.1056/NEJMoa2108891. Epub ahead of print. PMID: 34289274