June 2, 2022

Answering the latest questions on COVID-19 and vaccines

COVID-19 infections in Wayne, Macomb and Oakland counties remain high despite the availability of vaccines and boosters. For answers and recommendations, we turn to Teena Chopra, M.D., M.P.H., professor of Medicine in the Division of Infectious Diseases at the Wayne State University School of Medicine, and corporate medical director of Hospital Epidemiology, Infection Prevention and Antibiotic Stewardship at the Detroit Medical Center and Wayne State University.

Dr. Chopra, a founding member of the WSU Center for Emerging and Infectious Diseases, has been a leading source of COVID-19 information for Detroit and the nation during the pandemic, interviewed by countless newspapers, and radio and television stations. She also served on the Wayne State University Presidential Coronavirus Committee, assisting with preparations and response related to the virus.

Explain the concept of “herd immunity.”
The presence of large numbers of people in a community with immunity against a particular disease appears to be able to prevent epidemics of that disease – this effect is termed herd immunity. Herd immunity can be achieved by vaccination or natural infection.

Have we come close to reaching herd immunity in the United States, or in the Detroit region? If so many people are vaccinated and boosted, why are we seeing COVID-19 infection levels increasing?
Several factors can influence herd immunity, including the transmissibility of the virus (reproductive number), vaccination coverage in a population and effectiveness of vaccines to prevent infections. Emergence of SARS-CoV2 variants that escape vaccine-induced protection and natural immunity protection from previous infections can increase the number of susceptible individuals, therefore lowering herd immunity. In addition, waning vaccine-induced immunity might make it difficult to reach and maintain herd immunity.

Initially it was predicted that 70% of individuals in a population should be vaccinated to achieve herd immunity. However, with the emergence of the Omicron variant with increased transmissibility, greater immune evasion and lower vaccine effectiveness, a greater percentage of vaccination coverage will be required to achieve herd immunity. A recent study predicted that to establish herd immunity against the Omicron and other SARS-CoV2 variants with a reproductive number  greater than five, 90% vaccine coverage with a vaccine that is 90% effective in preventing infections will be required. However, effectiveness of currently available vaccines against the Omicron variant is only 22% to 44% (without boosters). This study, however, did not account for factors such as mask wearing, quarantine and testing followed by isolation, all of which can decrease the reproductive number.

Per the U.S. Centers for Disease Control and Prevention, 66.7% of the U.S. population is fully vaccinated and 46.7% have received a booster. For Michigan, those numbers are at 60% and 40%, respectively.

What version (variant) of COVID-19 are we on and what are the symptoms like now versus earlier versions? 
BA2, a sublineage of the Omicron variant, is currently predominant in the U.S., responsible for about 93% of infections. The rest of infections are due to other Omicron sublineages.

Omicron infections cause symptoms similar to other SARS-CoV2 variants. Runny nose, headache, sore throat and fatigue are the most common symptoms of Omicron. There is lower occurrence of fever, cough, or loss of sense of smell or taste in Omicron-infected patients. Also, a higher rate of asymptomatic carriage has been noted with the Omicron variant.

In southeast Michigan, should we still wear masks in public settings even if we’ve been vaccinated and boosted?
The CDC currently recommends that wearing masks in public should be based on local community transmission. Regardless of vaccination status, masks should be worn in public in areas with high community transmission.

In areas with moderate or low community transmission, mask wearing is optional. People who are immunocompromised or at high risk of severe illness should consider wearing masks when community transmission is moderate.

Community transmission levels are determined based on new COVID-19 cases and new COVID-19 hospitalizations in the last seven days per 100,000 population.
Given high levels of community transmission in southeast Michigan, I would recommend wearing masks in public settings.

Are fewer people being hospitalized even after testing positive?
Studies from several countries indicate that Omicron infections appear to be milder when compared to Delta infections. By use of three disease surveillance systems, the CDC noted that in the U.S. the percentage of hospitalization were lower during the Omicron pandemic than during the Delta pandemic. The hospitalization-to-case ratio was 27 per 1,000 cases during the Omicron period compared to 78 per 1,000 cases during the Delta period.

Are fewer people dying from COVID-19? Why is that? 
It appears that Omicron infections are associated with less mortality. In a large health care database compromising 199 hospitals, the in-hospital deaths among COVID-19 patients were 12.3% during the Delta period and 7.1% during the Omicron period. Similarly, in an academic hospital in Los Angeles, in-hospital deaths were noted in 8.3% of patients during the Delta predominance period compared to 4% during Omicron predominance period.

Some of the reasons for less illness severity with the Omicron variant include an increase in vaccination coverage, use of vaccine boosters and protection provided through previous infections. Studies also indicate potential lower virulence of the Omicron variant. The lower replication rate of Omicron in lung tissue could also result in better prognosis.

Is there anything new within the current booster to effect the current virus version? 
The formulation of the booster dose is similar to the primary series. mRNA vaccines are preferred for booster dose. For persons ages 5 to 49, a single booster dose is recommended. For those 50 years or older, a second booster dose four months after the first booster dose is recommended.

Are screenings like the home test really able to diagnose COVID-19, or is a PCR test better? 
PCR is the most sensitive test to diagnose COVID-19. Antigen tests, including home tests, have acceptable sensitivity in patients with symptoms of COVID-19, especially when testing is performed within a few days of symptom onset. The low sensitivity of antigen tests with some variants and in asymptomatic individuals makes them unreliable, and PCR will be preferred in such individuals. Also, there are instances when a positive or negative antigen test will need confirmation with PCR. The advantage of antigen tests include the short turnaround time and ability to perform at point-of-care or at home.

Can people be infected after they’ve been vaccinated and boosted? Are the effects of infection weaker for those who have been vaccinated and boosted? 
Yes, vaccinated and boosted individuals can get infected with COVID-19, but vaccination still confers protection against severe disease and death, including when the disease is caused by variants.

Variants such as Omicron have significant mutations in the spike protein that help them overcome the antibody neutralization conferred by vaccines. The neutralization antibody titers increase severalfold following booster vaccinations, which correlates with added protection against infection and severe disease following boosters.

Can people be reinfected after they’ve already had COVID-19 once? How many times is it possible to be reinfected?
Reinfections can occur in persons with previous COVID-19 infection. Reinfections constituted only 0.2% to 0.3% of all infections during earlier pandemic waves. This has increased to 6.8% during the Omicron surge.

Depending upon the earliest time after the initial infection when patients are deemed eligible for reinfections (60 vs. 90 days) as many as four to seven reinfection episodes have been noted.

Who is eligible for the antibody infusion? What will it do? Can I ask for it? 

Non-hospitalized persons with mild to moderate COVID-19 who are at high risk of disease progression are recommended to get monoclonal antibody infusions. These high-risk individuals include those 65 and older and those with underlying medical conditions determined to be high risk for severe COVID-19. Ideally these infusions should be given as soon as possible and within seven days of symptom onset.

These antibodies act by binding to the spike protein of SARS-CoV2 and block spike protein attachment to the human ACE2 receptor, thereby interfering with viral entry.

Looking forward, do you think we may require a twice-annual or annual vaccination, just as with an annual flu shot?
The risk of infection in vaccinated/boosted individuals has been noted to increase with time since last vaccine/booster dose due to waning antibody titers. When comparing the first two months vs. more than four months after the third dose, the vaccine effectiveness against hospitalization reduced from 91% to 78%. One observational study showed that when compared to three doses of mRNA vaccine, a fourth dose among persons 60 and older who had received their third dose at least four months earlier provided short-term protection against PCR-confirmed infection, symptomatic infection and severe outcomes, including death due to COVID-19. In another study, a fourth dose administered at similar intervals to healthy young health care workers only showed marginal benefits compared to a third dose.

Based on these findings, it appears annual or twice-annual vaccination might be needed if there is continued circulation of variants such as Omicron with reduced vaccine efficacy. Older individuals and those with comorbidities might derive the most benefit and might need doses at more frequent intervals.

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