Hot Topics in Infection Prevention: Vaccines Block COVID-19 Infection

April 13, 2021
Saskia v. Popescu, PhD, MPH, MA, CIC
Saskia v. Popescu, PhD, MPH, MA, CIC

Those fully vaccinated had 90% protection against infection regardless of symptoms and even partial immunization yielded 80% protection against infection.

Things are a bit precarious right now with COVID-19 cases rising in some areas and a race to vaccinate as many as possible. Over 167 million doses have been administered, with 62 million people fully vaccinated within the United States. Of the total population, this accounts for 18.8%, which is a very exciting milestone. Many of the vaccine manufacturers are working to ramp up production as well as study the efficacy in adolescents.

Effectiveness of mRNA COVID-19 Vaccines in Preventing Infection

One of the big questions we’ve had since the announcement of efficacious vaccines is—will this protect against infection as well as disease? While they are effective against severe disease and hospitalization, what about asymptomatic infection? This continued question is not easy to answer but one that we’re increasingly coming up against.

A new study published in Morbidity and Mortality Weekly Report (MMWR) assessed both the Pfizer and Moderna vaccines against SARS-CoV-2 infection in health care workers, first responders, and essential workers.

Coined the HERS-RECOVER study, this longitudinal cohort was across 8 locations in the United States that performed surveillance in vaccinated individuals for not only symptoms, but participants also “self-collected a midturbinate nasal swab weekly, regardless of COVID-19–associated illness symptom status and collected an additional nasal swab and saliva specimen at the onset of COVID-19–associated illness.” Investigators noted that “among 5077 participants, those with laboratory documentation of SARS-CoV-2 infection before enrollment starting in July 2020 (608) or identified as part of longitudinal surveillance up until the first day of vaccine administration (240) were excluded. Another 279 were excluded because of low participation (i.e., failed to complete surveillance for ≥20% of study weeks and did not contribute COVID-19–associated illness specimens). Overall, 3950 participants in the vaccine effectiveness analytic sample were analyzed.”

The participants included physicians, nurses, health care personnel, and 62% were female. 75% of the participants received at least one dose during the study period and overall, 5.2% were diagnosed with SARS-CoV-2 infection via RT-PCR.

“During the 116,657 person-days when participants were unvaccinated, 161 PCR-confirmed infections were identified (incidence rate = 1.38/1,000 person-days). During the 13 days after first-dose or second-dose vaccination when immune status was considered indeterminate (67,483 person-days), 33 PCR-confirmed infections were identified and excluded from the outcome. Two sources of partially immunized person-days were reported.”

After studying these frontline responders for 13 weeks across the 8 locations, these 3950 participants helped shed some important insight into protection against infection. Under these real-world conditions, those fully vaccinated had 90% protection against infection regardless of symptoms and even partial immunization yielded 80% protection against infection. More research will be needed, but this is a very promising beginning.

CDC SARS-CoV-2 Fomite Transmission Update

This week the Centers for Disease Control and Prevention (CDC) released a new scientific update on surface transmission and indoor community environments. The topic of “over cleaning” and “hygiene theater” has been used a lot in recent months as we learn more that fomite transmission is possible, but generally lower risk. From the infection prevention and epidemiologist perspective, it’s important to note that when dealing with a novel respiratory pathogen, we treat it like previous ones—fomite transmission is possible and more common in influenza, RSV, and was a concern during previous coronavirus outbreaks.

Hygiene theater and the focus on over cleaning did become an issue as people were bleaching groceries and quarantining mail, but the bigger concern is now how we communicate this. It’s still important to clean and disinfect and use hand hygiene. The CDC reiterates that “people can be infected with SARS-CoV-2 through contact with surfaces. However, based on available epidemiological data and studies of environmental transmission factors, surface transmission is not the main route by which SARS-CoV-2 spreads, and the risk is considered to be low. The principal mode by which people are infected with SARS-CoV-2 is through exposure to respiratory droplets carrying infectious virus.” Cleaning and disinfection are still recommended within 24 hours after an infectious person has been present in an indoor community. The CDC also reiterated that source control (masking) is a great way to avoid contamination, just like hand hygiene and other efforts to avoid bioburden.