Editor's Note: The Villager is reprinting the following essay by EAMC infectious disease specialist Dr. Ricardo Maldonado, which was shared by East Alabama Medical Center last week, in order to provide the most clear information straight to readers from area experts.
A lot was discussed about herd immunity early during the pandemic. Herd immunity occurs when a large portion of a community (the herd) becomes immune to a disease, making the spread of disease from person to person unlikely. As a result, the whole community becomes protected, not just those who are immune.
Herd immunity could be achieved “naturally” by people getting infected and recovering from it. The prevalence in the U.S., however, suggests we are very far from reaching herd immunity (becoming immune by getting sick, not through a vaccine).
New York has the highest prevalence at around 22 percent while other places are much lower —probably between 3 to 4 percent. That’s considerably a long way off from the 70 percent needed to achieve herd immunity.
In the U.S., almost 200 million people would need to be infected to get to the threshold of herd immunity. In the U.S., people at very low risk of dying from Covid-19 (younger than 30 years of age) account for almost 120 million. Clearly, to have 200 million people infected and recovered would mean that many people from age populations considered at risk would have to get sick as well, and many of them would die from it. Herd immunity through illness is not a good solution in terms of public health.
We are glad the CDC reviewed the recently revisited guidelines for testing and quickly reversed their recommendations. We were concerned because of the confusion that was created when it was suggested that asymptomatic exposed individuals do not necessarily need to be tested. This clarification is vital as we all know how important it is to understand the levels of asymptomatic transmission.
The timing of testing on asymptomatic exposed individuals should ideally be a minimum of five days after exposure because of the time it takes for incubation (usually five to 10 days for most patients).
On another note, new testing methods will be available soon, including saliva tests. Currently, we are mainly using antigen tests as they are more readily available, less expensive and faster than PCR testing. These tests are not perfect, but we should not let “the perfect be the enemy of the good.” These tests are still very good for mitigation strategies.
The fatality ratio of Covid-19, which estimates the proportion of deaths among all infected individuals, is still not totally known. That’s because it depends on the number of asymptomatic cases, and while that number appears to be high, it is not definitive as many of these persons do not get tested. Initially, the infection fatality ratio for Covid-19 was estimated to be almost 3 percent, but that was probably overestimated.
Covid-19’s fatality ratio will likely end up around 1 percent, clearly still more than the seasonal flu. Covid-19 has killed 2-5 times more people than the seasonal flu in just six months.
However, Covid-19’s fatality ratio will be less than SARS (severe acute respiratory syndrome), which had a worldwide fatality ratio of 10 percent from 2002-2004. It will also be less than MERS (Middle East respiratory syndrome), which killed about 37 percent of people who contracted it in the past seven years — none were in the United States.
While the Covid-19 fatality rate is much lower than SARS or MERS, it has a high transmission rate and a moderate fatality ratio. For that reason, it will infect many more people than SARS or MERS and end up killing many more people than either of those two viruses.
Most patients who recover from Covid-19 will be immune for some time, but we still don’t know how long the immunity will last. The reason we don’t know is because we are only six months into the pandemic. We will need 1-2 years to really see and have a good sense of the landscape of immunity. There is a recent report that appears to describe a true re-infection case in China. Even if that is true, we simply do not know how often this happens or if that is a rare circumstance. Time will tell us. For the sake of comparison, the other human “common cold” coronaviruses give an immunity that lasts between six to 12 months.
Corticosteroids improve survival in patients with hypoxemia, but are not likely to help in early stages of the infection. Remdesivir might shorten duration of symptoms, especially if used early enough. Convalescent plasma has moderate positive effects and appears safe. Many other therapies, such as easy-to-use oral antivirals, monoclonal antibodies, etc., are in clinical trials for prevention and early treatment of patients at risk for serious illness. Stay tuned.
Herd immunity from a vaccine is a promising approach as we know there are at least two vaccines that look hopeful. Phase III Covid-19 vaccine trials in the United States began July 27 with both the Moderna vaccine and the Pfizer/BioNTech vaccine.
Both vaccine studies are each enrolling 30,000 volunteers, with half receiving a placebo. Given that both require two doses separated by either 28 days (Moderna) or 21 days (Pfizer/BioNTech), the timeline for completing enrollment for the first dose bears watching in order to estimate when the second dose will be complete for all 30,000 volunteers in each of these two studies. Full safety assessment, immunogenicity measures, and vaccine efficacy determination will require some time after the second dose is given.
If enrollment and both doses given occur without any delays, then it seems possible we could have a vaccine available by early 2021.These two vaccines will likely be in a “horse race” with the Oxford Vaccine from the United Kingdom, so stay tuned for updates as we look to a vaccine to help better control the spread of Covid-19.
Until therapies improve and vaccines are available — and prove to be safe and effective — we just need everyone to keep doing the right things: keep social distancing, keep washing your hands frequently, and we especially need your help in wearing your masks in public. It saddens me that some people still question the efficacy and safety of face masks. I believe the mask mandate has all but proved that masks decrease transmission. Remember, a mask does help protect the person wearing it, and equally importantly, it helps protect others.
Ricardo Maldonado, M.D. is an Infectious Diseases specialist and is the sole practitioner with East Alabama Infectious Disease. He joined the medical staff at EAMC in 2009. Dr. Maldonado is leading the clinical response to COVID-19 at East Alabama Medical Center.