What is Covid breakthrough infections? Are the unvaccinated putting fully vaccinated people at risk?

New Delhi, July 30: As the delta variant makes a deadly sweep through unvaccinated people, these so called breakthrough cases are drawing more attention.

This new wave of anxiety is coming at a time when many people both (the vaccinated and the unvaccinated) are weary of the pandemic and ready to return to any semblance of normalcy.

A breakthrough infection is a case of illness in which a vaccinated individual becomes sick from the same illness that the vaccine is meant to prevent.

No vaccine provides 100 percent protection against infection, so breakthrough cases are not new, and not unique, to COVID-19.

Breakthrough infections identified

Breakthrough infections have been identified in individuals immunized against a variety of different diseases including Mumps, Varicella (Chicken Pox), and Influenza.

The character of breakthrough infections is dependent on the virus itself. Often, the infection in the vaccinated individual results in milder symptoms and is of a shorter duration than if the infection was contracted naturally.

What CDC says about the possibility of COVID-19 illness after vaccination

According to Centers for Disease Control and Prevention (CDC) which is currently monitoring and investigating all reports of COVID-19 breakthrough cases say a small percentage of people who are fully vaccinated will still get COVID-19 if they are exposed to the virus that causes it. These are called "vaccine breakthrough cases." This means that while people who have been vaccinated are much less likely to get sick, it will still happen in some cases. It's also possible that some fully vaccinated people might have infections, but not have symptoms (asymptomatic infections). Experts continue to study how common these cases are.

Other reasons why fully-vaccinated people might get COVID-19

It's possible a person could be infected just before or just after vaccination and still get sick. It typically takes about 2 weeks for the body to build protection after vaccination, so a person could get sick if the vaccine has not had enough time to provide protection.

New variants of the virus that causes COVID-19 illness are spreading in the United States. Current data suggest that COVID-19 vaccines authorized for use in the United States offer protection against most variants. However, some variants might cause illness in some people after they are fully vaccinated.

Defining a vaccine breakthrough infection

For the purpose of this surveillance, a vaccine breakthrough infection is defined as the detection of SARS-CoV-2 RNA or antigen in a respiratory specimen collected from a person ≥14 days after they have completed all recommended doses of a U.S. Food and Drug Administration (FDA)-authorized COVID-19 vaccine.

How serious is a COVID-19 breakthrough infection?

The CDC defines a vaccine breakthrough infection as one in which a nasal swab can detect the SARS-CoV-2 RNA or protein more than 14 days after a person has completed the full recommended doses of an FDA-authorized COVID-19 vaccine.

Note that a breakthrough infection doesn't necessarily mean the person feels sick - and in fact, 27 per cent of breakthrough cases reported to the CDC were asymptomatic. Only 10 per cent of the breakthrough-infected people were known to be hospitalised (some for reasons other than COVID-19), and 2 per cent died. For comparison, during the spring of 2020 when vaccines were not yet available, over 6% of confirmed infections were fatal.

CDC data also found that women account for 63 per cent of breakthrough infections. Some smaller studies identified women as the majority of breakthrough cases as well.

Are the vaccines failing to protect? Or are the unvaccinated now putting the vaccinated at risk?'

According to health experts rare "breakthrough infections" among vaccinated people are not a sign that vaccines are failing. Instead, they are a warning of how vaccine holdouts can endanger even their inoculated neighbors.

The comments were made by Dr Drew Weissman, professor of medicine at University of Pennsylvania's Perelman medical school, who, along with his long-time collaborator Dr Katalin Kariko, is credited with the research that underpins the success of mRNA vaccines by Pfizer-BioNTech and Moderna.

How do variants like delta change things?

Since then new variants like Delta have emerged, many of which are better at dodging the antibodies produced by the currently authorized vaccines. While existing vaccines are still very effective against these variants for preventing hospitalization, they are less effective than against previous variants.

Two doses of the mRNA vaccines were only 79 per cent effective at preventing symptomatic disease with delta, compared with 89 per cent effective in the case of the earlier alpha variant, according to Public Health England. A single dose was only 35 per cent protective against delta.

About 12.5 per cent of the 229,218 delta variant cases across England through July 19 were among fully vaccinated people.