Results from tracking of fully vaccinated individuals suggest that while risk of infection remains small, positive tests may be due to virus mutations.
Starting in February, as part of a CDC assessment study officials in Chicago began following vaccinated nursing home residents and staff to detect breakthrough infections after one such case was identified. Breakthrough cases are when a fully vaccinated person later gets the virus they were vaccinated against.
This investigation was undertaken in order to prevent any subsequent outbreaks of COVID-19 in these types of high risk facilities. City wide nursing homes had been advised to test all residents at least monthly. Staff were tested twice a week until early February, and then tested weekly for most of through the end of March.
There were 627 confirmed cases of SARS-CoV-2 in 75 nursing homes. Of these cases, 447 involved residents and staff who had not been vaccinated at all, 145 involved individuals who had received only one dose, and 13 involved individuals who had gotten their second shot less than two weeks prior.
Among the remaining 22 individuals identified with definite breakthrough infections, 12 were residents and 10 were staff. Fourteen of these cases were asymptomatic, four required hospitalization, and one, a resident, proved fatal. The resident who died also had a bacterial bloodstream infection as well as a urinary tract infection, plus multiple chronic conditions which are known to increase the risk for severe COVID-19.
Six people with breakthrough infections had a previous positive COVID-19 more than 90 days before being identified with a breakthrough infection and five if these people had a negative test result between the two positive results. There was one individual who had tested positive previously who had a negative test less than 14 days prior to testing positive for a breakthrough infection.
The CDC investigators of this study did not attempt to estimate vaccine efficacy from these data. Additionally, although some samples were submitted for genetic sequencing to identify possible variant strains and mutations, results are pending.
With the growing number of people becoming fully vaccinated, learning if new infections in this population are due to the original COVID-19 virus or involve mutations of this virus is becoming a focus of increasing attention. Illinois has been monitoring cases of COVID-19 to determine if breakthrough cases involve mutations and if so which mutations in order to determine how effective vaccines are against variants of the virus.
Looking at the state of Illinois overall, more than 580 fully vaccinated Illinois residents out of around 2.5 million have tested positive for COVID-19 as of April 7th.
A spokesperson from the Illinois Department of Public Health stated, “We're looking to report breakthrough data once a week, but are waiting for more information from the [Centers for Disease Control and Preventions]."
Dr. Anthony Fauci, the Director of the National Institute of Allergy and Infectious Disease recently remarked that whenever tens of millions of people are vaccinated against a virus that is active in the population you are bound to see some breakthrough infections. He said it shouldn’t be surprising that we are seeing some such cases now, as none of the vaccines being administered are 100 percent effective at preventing infections.
Fauci added that “one of the important things that will be done, and must be done, is to sequence the genome of the virus that’s the breakthrough virus” in order to find out whether the infection is from the original virus strain or one of the COVID-19 variants.
Currently it appears that the authorized vaccines diminish the severity of infection regardless of the virus strain. This is why experts say it is of utmost importance for even people previously infected with COVID to get vaccinated as they are aware that people can contract the virus more than once. Knowing whether breakthrough cases were caused by the virus the vaccines were designed to protect against or by new variants would help scientists decide how best to approach future vaccinations and booster shots. If a variant that is leading to concern breaks through, health experts could determine that it’s important to develop a vaccine targeting the variant’s mutations. If the virus is one that the community has already been exposed to, but it seems that immunity is waning, scientists might suggest a booster shot of the same vaccine be administered.
More than 7.1 million COVID-19 vaccines have been administered in Illinois. More than 2.8 million have been fully vaccinated. That's about 23 percent of the state's total population.